# Intra-wet season variation in rangeland fodder quality influences feed conversion, growth and methane emissions in West African zebu cattle

Gérard Xavier Gbenou, Boko Michel Orounladji, Luc Hippolyte Dossa, Denis Bastianelli, Ollo Sib, Bienvenu d'Ela Somda, Palipougni Diabri, Florentin Sanou, Souleymane Sanogo, Laurent Bonnal, et al.

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## ► To cite this version:

Gérard Xavier Gbenou, Boko Michel Orounladji, Luc Hippolyte Dossa, Denis Bastianelli, Ollo Sib, et al.. Intra-wet season variation in rangeland fodder quality influences feed conversion, growth and methane emissions in West African zebu cattle. Journal of Agriculture and Food Research, 2026, 26, pp.102670. 10.1016/j.jafr.2026.102670. hal-05490306

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Submitted on 3 Feb 2026

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# Intra-wet season variation in rangeland fodder quality influences feed conversion, growth and methane emissions in West African zebu cattle

Gérard Xavier Gbenou<sup>a,b,c</sup>, Boko Michel Orounladji<sup>a,b,c</sup>, Luc Hippolyte Dossa<sup>a,c</sup>, Denis Bastianelli<sup>b,d</sup>, Ollo Sib<sup>b,c,d</sup>, Bienvenu D'Ela Somda<sup>d</sup>, Palipougni Diabri<sup>d</sup>, Florentin Sanou<sup>d</sup>, Souleymane Sanogo<sup>d</sup>, Laurent Bonnal<sup>b,d</sup>, Paulo Salgado<sup>b,d</sup>, Alexandre Ickowicz<sup>b,d</sup>, Philippe Lecomte<sup>b,d</sup>, Mohamed Habibou Assouma<sup>b,c,d,w,d</sup>

## ARTICLE INFO

### Keywords:

- Natural pasture quality
- Cattle
- Enteric methane
- Feed conversion ratio
- Livestock productivity
- Sub-saharan Africa

## ABSTRACT

Livestock in sub-Saharan Africa is a major contributor to greenhouse gas emissions, particularly enteric methane (eCH4), with emissions intensities and yield often elevated. In this region, wet-season rangeland fodder is the primary feed source for livestock. This study evaluated the effects of fodder growth stage and feed allowance on feed intake, digestibility, average daily gain (ADG), feed conversion ratio (FCR), and eCH4 emissions in cattle. Over a 112-day period, including a 14-day adaptation and a 98-day data collection phase, ten Sudanese Fulani zebu bulls (52 ± 1.2 months of age, 195 ± 14.6 kg body weight) were fed green rangeland fodder. They were divided into two groups of five animals each: one received fodder at a high allowance level of 4.5 % of body weight (BW) dry matter (DM) basis (4.5ING), while the other received 2.5 % of BW (2.5ING). Voluntary intake, digestibility, and eCH4 (GreenFeed®) were measured daily across three fodder growth stages: vegetative stage (VeS), reproductive stage (ReS), and mature stage (MaS). ADG and FCR were assessed fortnightly. DM intake decreased progressively from VeS to MaS with the highest values recorded for 4.5ING (P < 0.05). Digestibility was affected only by growth stage, decreasing from VeS to MaS (P < 0.05). Both ADG and FCR were influenced by fodder growth stage and feed level. The lowest eCH4 yield and intensity were observed in VeS (P < 0.05). Fodder level influenced eCH4 intensity (P < 0.05). Intra-wet season fodder growth stage significantly affected intake, digestibility, growth, and eCH4 emissions in cattle, while feed allowance influenced performance and eCH4 intensity. Significant interactions effects were observed between fodder growth stage and feed allowance for all parameters except digestibility. The best animal performance, along with the lowest eCH4 yield and intensity were observed in 4.5ING animals during VeS. These findings suggest that optimizing feed availability at the beginning of the wet season is an effective feeding strategy to enhance productivity while mitigating methane emissions in extensive livestock systems.

## 1. Introduction

Sub-Saharan Africa (SSA), a region characterized by predominantly extensive livestock production systems, is particularly vulnerable to environmental and climatic issues [1]. Within this context, cattle farming serves as acritical livelihood and food security mechanism for millions of families [2]. However, it also represents a significant source of greenhouse gas (GHG) emissions, primarily through enteric methane

(eCH4) emissions released during ruminal fermentation. Enteric methane (eCH4) can account for 50-60 % of a livestock system's total carbon emissions, depending on the type of ruminant livestock system [3]. Due to its substantially higher global warming potential compared to carbon dioxide (CO2), eCH4 constitutes a key concern in climate change mitigation efforts. Beyond its environmental impacts, eCH4 represents a considerable loss of dietary energy that could otherwise be utilized for animal metabolism. This energy loss reduces feed-use

<footnote><sup>a</sup> Laboratoire des Sciences Animales, Faculté des Sciences Agronomiques, Université d'Abomey-Calavi, BP 526, Cotonou, Benin</footnote>

<footnote><sup>b</sup> SELMET, University of Montpellier, CIRAD, INRAE, Institut Agro, Montpellier, France</footnote>

<footnote><sup>c</sup> CIRAD, UMR SELMET, dP ASAP, 01 BP 454, Bobo-Dioulasso, Burkina Faso</footnote>

<footnote><sup>d</sup> Centre International de Recherche Développement sur l'Elevage en zone Subhumide, 01 BP 454, Bobo-Dioulasso, Burkina Faso</footnote>

<footnote>* Corresponding author. SELMET, University of Montpellier, CIRAD, INRAE, Institut Agro, Montpellier, France.
E-mail address: habibou.assouma@cirad.fr (M.H. Assouma).</footnote>
efficiency and constrains the productive performance of ruminant livestock [4]. The magnitude of these emissions is modulated by various factors, notably the quality and availability of fodder, which are subject to pronounced seasonal fluctuations [5].

Pastoralism, defined as the extensive grazing of livestock on natural rangelands, constitutes the dominant livestock system in West Africa. The wet season plays a crucial role in sustaining productivity within pastoral and agropastoral systems by stimulating rapid vegetation growth and enhancing fodder availability [6]. However, this season is also marked by fluctuations in the nutritional composition of forage [7], which significantly influences ruminants' feed intake and digestion, thereby modulating eCH₄ emissions. Indeed, during the wet season, these nutritional fluctuations are linked to the dynamics of rangeland fodder development. As forage progresses through its growth stages, significant changes occur in plant structure and chemical composition [8] which in turn affect feed quality and animal intake [9]. While seasonal contrasts, particularly between dry and wet periods, are well-documented drivers of eCH₄ variability [5,10,11], emerging evidence highlights the importance of intra-seasonal dynamics. For instance, Gbenou et al. [5] observed that eCH₄ emissions fluctuate in response to rangeland forage availability. In the wet season, discrepancies between actual and estimated intake capacities suggest that vegetation growth may exert a more complex influence on emission patterns. Advancing our understanding of how forage development during the wet season affects intake behavior, nutrient assimilation, and eCH₄ output is therefore critical to refining annual emission estimates in the region. This study investigates wet-season patterns of feed intake, digestibility, average daily gain, feed conversion ratio, and eCH₄ emissions in Sudanese Fulani zebu cattle, with a focus on their relationship to natural rangeland fodder growth dynamics. Based on this, it was hypothesized that wet-season rangeland fodder quality affects feed intake, digestibility, and growth performance; that feed allowance modifies the effects of fodder growth stage on feed conversion and performance; and that fodder growth stage and feed allowance interact to influence eCH₄ emissions and emission intensity.

## 2. Methodology

### 2.1. Experimental site

The experiment was conducted at the CIRDES (Centre International de Recherche-Développement sur l'Elevage en zone Subhumide) experimental station in Bobo-Dioulasso, located in the Guiriko region of Western Burkina Faso (11°10'37" N and 4°17'52" W). The facility comprised a ventilated barn measuring 25 × 10 m and is situated within a tropical subhumid climate zone. The region experiences an average annual temperature of 26 ± 0.5 °C and receives approximately 691 mm of rainfall, distributed across three seasons: a wet season (May to October), a cool dry season (November to February), and a hot dry season (March to May). The present study was carried out during the wet season, spanning from July 10 to October 15, 2023.

### 2.2. Animals, feed, and experimental design

Ten Sudanese Fulani zebu bulls, aged 52 ± 1.2 months and weighing 194.6 ± 14.6 kg, were initially included for this study. The animals were housed individually in 9 m² pens within the experimental barn. Their diet consisted of freshly harvested green fodder sourced from natural rangelands, predominantly composed of *Andropogon gayanus* Kunth (Poaceae), a perennial C4 grass widely distributed across the West African Sudanian zone, and particularly abundant during the wet season. Minor components included associated grasses and some herbaceous legumes, reflecting the typical botanical composition of natural rangelands in the region [12].

Fodder was harvested daily from the production site in the rural commune of Bama, approximately 20 km from Bobo Dioulasso

(11°23'05" N and 4°25'04" W), as it progressed through the various stages of growth. The soils at the site are tropical ferruginous, with an acidic pH (5.5-6.5) and a silt-sandy to clay-sandy texture characterized by active leaching of nutrients. The median soil organic carbon content in this region is 0.85 % and the median soil organic matter content is 1.46 % [13]. The vegetation is dominated by wooded and tree-covered savannahs.

The fodder growth stages were classified according to morphological and physiological criteria commonly applied to tropical grasses [14]: the vegetative stage (VeS) was defined by the emergence of leafy shoots prior to stem elongation, with plant height below 40 cm, absence of inflorescences, and a high leaf-to-stem ratio; the reproductive stage (ReS) encompassed stem elongation and inflorescence development (booting to full flowering), with plant height ranging between 50 and 100 cm and a moderate decline in the leaf-to-stem ratio; the mature stage (MaS) corresponded to seed formation and partial senescence, characterized by dry leaves, reduced leaf-to-stem ratio, and declining biomass quality.

The animals were fed twice daily, at 08:30 a.m. and 4:30 p.m., with drinking water and mineral lick blocks provided *ad libitum*. The mineral lick blocks used (Reva mineral block®) is made of trace minerals detailed as raw ash (86.38), Calcium (1.1), Phosphorus (<0.5), Magnesium (0.44), and Sodium (34.2). A mixed experimental design was used. The feeding level (2.5 % and 4.5 % BW) served as a between-subjects factor. The ten bulls were randomly assigned to one of the two dietary treatments (n = 5 per treatment) based on dry matter (DM) offered levels: 4.5 % of BW (4.5ING) and 2.5 % of BW (2.5ING) from the beginning of the experiment, and stayed on the same feeding level throughout the study. The 2.5 % DM level was selected to replicate the 2.3 % BW ration tested by Gbenou et al. [5], which was found to underestimate intake capacity. To address this limitation, the 4.5 % BW level was introduced to approximate *ad libitum* feeding conditions. The experiment spanned 16 weeks, including a two-week adaptation period followed by 14 weeks of data collection on BW, feed intake, nutrient digestibility, feed conversion ratio, and GHG emissions, with a particular focus on eCH₄.

### 2.3. Measurements

#### 2.3.1. Body weight, refusals, and total feces

The BW was measured biweekly throughout the 14-week data collection period to calculate average daily gain (ADG). Each animal's daily diet, based on either 4.5 % or 2.5 % of BW on a DM basis, and corresponding refusals were weighted to determine voluntary feed intake. Representative samples of both offered and refused feed were collected daily and stored separately. All samples were immediately oven-dried at 55 °C for 72 h to estimate DM content and subsequently ground to 1 mm (mill: SM 100, Retsch GmbH, Hann, Germany) for chemical analysis. In total, 98 representative samples of offered feed (300g each) and 980 samples of refusals (300g each) were collected (i.e., 14 weeks × 7 days/week × 10 animals). These data were used to estimate the chemical composition of the ingested feed.

Following the protocol established by Gbenou et al. [5,15], each animal was fitted with a fecal collection bag, to which they had been acclimated during the feed adaptation phase, in order to collect total daily feces individually. Daily fecal output was recorded, and an 800g representative sample per animal was collected, dried, and stored separately for subsequent analysis.

#### 2.3.2. Enteric methane and carbon dioxide emissions measurements

Emissions of CO₂ and eCH₄ were measured using the GreenFeed® system (GF - ID: 252, C-Lock Inc., SD, USA). The animals were not specifically trained for this experiment, as they had previously participated in several studies and were already accustomed to GreenFeed® measurements. During each animal visit, the device dispensed bait at a rate of 31g of DM/minute, with a daily maximum of 464 g of DM/
animal. The bait consisted of a 90:10 mixture of rangeland fodder and molasses, formulated to minimize its influence on feed intake, digestibility, and gas emissions. Prior to mixing, the fodder was ground to pass through a 1 mm sieve, and the final blend was pelleted to an 8 mm diameter. The bait contained 88.1 g/kg DM of organic matter (OM), 35.6 g/kg DM of crude protein (CP), 531.9 g/kg DM of neutral detergent fiber (NDF), 359.1 g/kg DM of acid detergent fiber (ADF), 68.8 g/kg DM of acid detergent lignin (ADL), and 18.3 MJ/kg DM of gross energy (GE).

To account for bait consumption in daily feed intake calculations, refusals were collected and weighed per animal after each GF visit. Animals accessed the GF five times daily, at 06:30 a.m. (overnight fast), 10:00 a.m. (immediately after feed intake), 2:00 p.m. (during rumination), 6:00 p.m. (immediately after feed intake and at sunset) and 9:00 p.m. (night), in alignment with typical animal eating behavior. Green-Feed® measurement times were scheduled to coincide with the key physiological and behavioral phases of cattle's daily feeding and rumination cycle. Each animal completed 490 visits over the course of the study, substantially exceeding the visit counts reported by Manafiazar et al. [16] and Gbenou et al. [5,15,17], who recorded 20–29 visits. On average, each animal spent 3 min ±17 s per measurement, which falls within the range (2 min 01 s to 6 min 14 s) reported by Beck et al. [18] in a meta-analysis.

Daily calibration of the GF system was performed at 04:00 a.m., when no animals were present. A certified gas mixture was injected at recommended concentrations ($CH_4$: 0.509 ppmv, $CO_2$: 4.993 ppmv, $H_2$: 0.010 ppmv and $O_2$: 0.021 ppmv; Liquide Air, C-Lock Inc., USA) to verify sensor accuracy. $CO_2$ recovery tests were conducted twice weekly, and the system's filter was replaced whenever the airflow dropped below 27 L/s. Throughout the study, the average recovery rate was 97.4 ± 1.02 % (Min = 93.90, Max = 99.79), wind direction averaged 136.3 ± 56.72 (Min = 4.38, Max = 355.38), and airflow was maintained at 38.3 ± 2.75 L/s (Min = 25.87, Max = 38.30).

### 2.3.3. Determination of diets and feces DM and chemical composition

As described by Gbenou et al. [5,15], the chemical composition of both offered and refused forages, as well as fecal matter, were predicted using near-infrared spectroscopy (NIRS) at CIRAD (Baillarguet, France). For forage samples, the parameters analyzed included ash, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), gross energy (GE), and *in vitro* digestibility of dry matter (IVDMd) and organic matter (IVOMd). Fecal samples were analyzed for ash, nitrogen, NDF, ADF, ADL, and GE.

Fibres (NDF, ADF, ADL) were analyzed following the sequential method described by Van Soest et al. [19] using an Ankom fibre analyser (Ankom® Tech. Co., Fairport, NY, USA). The NDF and ADF were corrected for ash measured on ADL residue. Ash content was determined by incinerating samples in a muffle furnace for 5 h at 550 °C [20]. Total nitrogen content was determined using the Kjeldahl method as in Has-soun et al. [20] and CP content was calculated as total nitrogen x 6.25. *In vitro* digestibility was determined using the pepsin-cellulase method [21]. Gross energy of offered and refusals was determined by bomb calorimetry (IKA calorimeter model C2000; IKA-Werke GmbH, Staufen, Germany).

The chemical composition of the ingested feed was subsequently estimated based on the differential between the offered and refused material. Table 1 presents the chemical characteristics of natural rangeland fodder across its growth stages.

## 2.4. Data processing and parameter calculation

### 2.4.1. Intake, digestibility, average daily gain and feed conversion ratio

Individual daily voluntary fodder intake was calculated as the difference between the quantity of feed offered and that refused. Daily bait intake from GreenFeed® was quantified individually. The chemical composition of the ingested diet intake and total feed intake (diet + bait) was estimated following the methodology of Gbenou et al. [5]. Apparent

<caption>**Table 1**</caption>

Chemical composition of natural green rangeland fodder offered at different growth stages to Sudanese Fulani zebu bulls.

<table><thead><tr><th>Item</th><th>VeS</th><th>ReS</th><th>MaS</th><th>SEM</th><th>P-value</th></tr></thead><tbody><tr><td>DM (%FM)</td><td>19.2<sup>B</sup></td><td>18.4<sup>B</sup></td><td>23.2<sup>A</sup></td><td>0.31</td><td>&lt;0.001</td></tr><tr><td>OM (%DM)</td><td>85.3<sup>B</sup></td><td>85.0<sup>B</sup></td><td>88.1<sup>A</sup></td><td>2.11</td><td>&lt;0.001</td></tr><tr><td>CP (%DM)</td><td>11.0<sup>A</sup></td><td>9.0<sup>B</sup></td><td>10.3<sup>A</sup></td><td>1.96</td><td>&lt;0.001</td></tr><tr><td>NDF (%DM)</td><td>61.7<sup>C</sup></td><td>63.1<sup>B</sup></td><td>64.9<sup>A</sup></td><td>2.89</td><td>0.004</td></tr><tr><td>ADF (%DM)</td><td>34.1<sup>B</sup></td><td>36.2<sup>A</sup></td><td>36.6<sup>A</sup></td><td>2.22</td><td>&lt;0.001</td></tr><tr><td>GE (MJ/kg DM)</td><td>18.2<sup>B</sup></td><td>18.1<sup>B</sup></td><td>19.4<sup>A</sup></td><td>0.06</td><td>&lt;0.001</td></tr><tr><td>IVDMd (%DM)</td><td>55.2<sup>A</sup></td><td>50.9<sup>B</sup></td><td>48.3<sup>C</sup></td><td>0.43</td><td>&lt;0.001</td></tr><tr><td>IVOMd (%OM)</td><td>51.1<sup>A</sup></td><td>47.6<sup>B</sup></td><td>43.5<sup>C</sup></td><td>0.42</td><td>&lt;0.001</td></tr></tbody></table>

VeS: vegetative stage, ReS: reproductive stage, MaS: maturity stage, SEM: standard error of the mean.

DM: dry matter, FM: fresh matter, OM: organic matter, CP: crude protein, NDF: neutral detergent fiber, ADF: acid detergent fiber, ADL: acid detergent lignin, GE: gross energy, MJ: megajoule, IVDMd: *in vitro* dry matter digestibility, IVOMd: *in vitro* organic matter digestibility.

A,B,C: Values with different superscripts within the same row differ significantly at P < 0.05: comparison between fodder stages.

digestibility was calculated daily using Equation (1), based on the relationship between intake and fecal excretion, allowing data to be aggregated by forage growth stage. The ADG was derived from biweekly BW measurements taken in the morning, prior to feeding, with animals weighed on an empty stomach, using Equation (2). Feed conversion ratio (FCR) was subsequently computed from intake and ADG values using Equation (3). Estimated Protein-Corrected-Meat Output (ePCMO) was calculated using Equation (4). This metric integrates ADG with carcass yield, edible yield, and protein content of meat. Specifically, a carcass yield of 51.54 % BW was applied, representing the mean of values reported for zebu cattle by Dumas and Lhoste [22]; 52.7 %) and Teye and Sunkwa [23]; 50.38 %). An edible yield of 67.86 % was adopted based on findings by Mummed and Webb [24] for African cattle. The protein content of edible meat was assumed to be 21 %, consistent with the average range of 19–23 % reported by Duchène et al. [25].

$$ \text{Apparent DM digestibility} = (\text{DM intake} - \text{DM excreted}) / \text{DM intake.} \qquad \text{Eq. 1} $$

$$ \text{ADG (g/day)} = (\text{Body weight after 2 weeks} - \text{Body weight}) / 14. \qquad \text{Eq. 2} $$

$$ \text{FCR} = \text{kg of DM intake / kg of ADG.} \qquad \text{Eq. 3} $$

$$ \text{ePCMO (g/day)} = \text{ADG} * \text{Carcass yield} * \text{Edible yield} * \text{Protein content.} \qquad \text{Eq. 4} $$

### 2.4.2. Daily gas emissions calculation

The C-Lock platform was updated with the raw emission data (n = 4900) generated by the GF for each gas. Measurements were excluded if visits lasted less than 2 min, if the animal's head position was suboptimal, or if sensor proximity fell below the threshold of 800 raw data points during the monitoring period. This has led to the removal of 124 records per gas. The remaining spot measurements of $eCH_4$ and $CO_2$, recorded per animal and per visit (n = 4776 per gas), were retained in the dataset provided by C-Lock. Outlier detection was performed using the linear regression method described by Coppa et al. [26], resulting in the exclusion of 0.73 % of the dataset per gas. This yielded a final sample of 4741 data points per gas for subsequent analysis. Individual daily gas flux values were calculated using Equation (5), which averaged emissions across all visits per animal per day, stratified by fodder level. Given the measurement schedule, three daytime readings (10:00 a.m., 02:00 p.m., and 06:00 p.m.) and two nighttime readings (06:30 a.m. and 09:00 p.m.), each time point was assigned equal weight in the averaging process. The methane conversion rate (Ym), representing the proportion
of gross energy intake (GEI) lost as eCH₄, was computed using Equation (6), following the guidelines of the IPCC [27]. Methane emission intensities were further calculated per animal using Equation (7) (kg eCH₄/kg ADG) and Equation (8) (g eCH₄/g ePCMO), providing metrics for emission efficiency relative to growth and ePCMO.

All graphical representations were generated using the ggplot2 and dplyr packages in R. Although the number of animals per treatment was limited (n = 5), the daily repeated-measures design over a 98-day period provided a robust estimation of how individual animals responded to both the level of DM offered and the growth stage of the fodder.

$$e\text{CH}_4 (\text{g/day}) = 0.5*[(e\text{CH}_4.10 : 00 \text{ a.m.} + e\text{CH}_4.02 : 00 \text{ p.m.} + e\text{CH}_4.06 : 00 \text{ p.m.}) / 3] + 0.5*[(e\text{CH}_4.06 : 30 \text{ a.m.} + e\text{CH}_4.09 : 00 \text{ p.m.}) / 2], \quad \text{with eCH}_4.\text{i} : \text{average eCH}_4 \text{ emissions (g/day) for visits over the same i period.} \quad \text{Eq. 5}$$

$$Y_m (\% \text{GEI}) = [(e\text{CH}_4 * 55.65 / 1,000) / \text{GEI}] \times 100, \text{ with eCH}_4 \text{ in g/day and GEI in MJ/day.} \quad \text{Eq. 6}$$

$$e\text{CH}_4 (\text{g/kg ADG}) = e\text{CH}_4 / \text{ADG}, \text{ with eCH}_4 \text{ in g/day and ADG in kg/day.} \quad \text{Eq. 7}$$

$$e\text{CH}_4 (\text{g/g ePCMO}) = e\text{CH}_4 / \text{ePCMO}, \text{ with eCH}_4 \text{ in g/day and ePCMO in g/day.} \quad \text{Eq. 8}$$

## 2.5. Data analysis

All statistical analyses were performed using R software version 4.4.2 [28]. Data were tested for normality using the Shapiro-Wilk test and for homogeneity of variances using Levene's test. A general linear model (GLM) procedure was used via the lme4 and lmerTest packages to evaluate the effects of fodder growth stage and fodder supply level on intake, digestibility, ADG, ePCMO, FCR, and gas emissions (CO₂ and eCH₄). Fixed effects included the fodder growth stage and the level of DM offered, as well as their interaction. Inter-individual variability was accounted for by incorporating animal identity as a random effect.

For each response variable, means and standard errors of the mean (SEM) were computed. When significant differences were detected (P < 0.05), pairwise comparisons were conducted using Duncan's multiple range test (duncan.test) implemented through the agricolae package. This post-hoc test is widely used in agronomy and animal nutrition research, making it perfect to identify significant differences among treatment.

The statistical model used for variance analysis was specified as follows:

$$Y_{ijk} = \mu + S_i + L_j + (S * L)_{ij} + (1|A_k) + \epsilon_{ijk}$$

where Yijk = response variable (e.g., feed component, intake, digestibility, ADG, ePCMO, FCR, CO₂, eCH₄);

μ = overall average;

Sᵢ = fixed effect of fodder growth stage (VeS, ReS, and MaS);

Lⱼ = fixed effect of fodder supply level (4.5ING and 2.5ING);

(S * L)ᵢⱼ = interaction between fodder stage and supply level;

Aₖ = random effect of individual animals (n = 10); and

εᵢⱼₖ = residual error.

# 3. Results

## 3.1. Rangeland fodder quality

The nutritional composition of the rangeland fodder offered to animals varied significantly across the fodder growth stages (Table 1), with all measured parameters showing statistically significant differences (P < 0.001). CP content was lowest during ReS, with fodder at the VeS containing 11 %DM, approximately 22 % higher than the 8.9 %DM recorded at ReS. In contrast, fiber fractions, including NDF and ADF, were lowest at VeS and ReS, and increased markedly at MaS, indicating a decline in forage quality as the season progressed.

## 3.2. Fodder intake

During the wet season, the interaction between fodder growth stage and feed allowance was statistically significant for DM intake (P < 0.05; Table 2). DM intake, including baits, varied significantly across the phenological stages of rangeland fodder, ranging from 13.58 to 49.27 g/ kg BW (P < 0.05). The lowest DM intake (24.9 g/kg BW) was observed at MaS. On average, was animals consumed 87 % and 96 % of offered feed in the 4.5ING and 2.5ING treatments, respectively (P < 0.05). In the 4.5ING group, DM intake (g/kg BW) decreased from the onset of VeS, remained relatively stable during ReS, and dropped again from the beginning of MaS. In contrast, intake in the 2.5ING group remained consistent throughout VeS and ReS before decreasing at MaS (Fig. 1). The highest DM intake was observed in 4.5ING treatment during VeS. Across all growth stages and feeding levels, the consumed feed consistently exhibited higher CP content than the refusals. At MaS, refusals were notably richer in fiber fractions, including NDF and ADF, compared to the ingested feed (Table 3).
<table><caption>**Table 2**

Daily intake of natural green rangeland fodder (including bait distributed by GF) in Sudanese Fulani zebu bulls across different growth stages.</caption><thead><tr><th rowspan="2">Item</th><th colspan="3">Fodder growth stage</th><th colspan="2">Feeding level</th><th colspan="6">Fodder growth stage * feeding level</th><th rowspan="2">SEM</th><th colspan="3">P-value</th></tr><tr><th>VeS</th><th>ReS</th><th>MaS</th><th>4.5ING</th><th>2.5ING</th><th>VeS * 4.5ING</th><th>VeS * 2.5ING</th><th>ReS * 4.5ING</th><th>ReS * 2.5ING</th><th>MaS * 4.5ING</th><th>MaS * 2.5ING</th><th>Fodder growth stage</th><th>Offered level</th><th>Fodder growth stage * Feeding level</th></tr></thead><tbody><tr><td>Fodder DMI (kg/d)</td><td>6.5<sup>B</sup></td><td>6.9<sup>A</sup></td><td>5.7<sup>C</sup></td><td>7.5<sup>a</sup></td><td>5.5</td><td>7.7<sup>w</sup></td><td>5.3<sup>yz</sup></td><td>8.1<sup>w</sup></td><td>5.6<sup>y</sup></td><td>6.4<sup>x</sup></td><td>5.1<sup>z</sup></td><td>0.03</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>Bait DMI (kg/d)</td><td>0.140<sup>B</sup></td><td>0.144<sup>B</sup></td><td>0.200<sup>A</sup></td><td>0.096<sup>a</sup></td><td>0.214<sup>b</sup></td><td>0.072<sup>z</sup></td><td>0.207<sup>x</sup></td><td>0.080<sup>z</sup></td><td>0.207<sup>x</sup></td><td>0.162<sup>y</sup></td><td>0.237<sup>w</sup></td><td>0.000</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>DMI (kg/d)</td><td>6.6<sup>B</sup></td><td>7.0<sup>A</sup></td><td>5.9<sup>C</sup></td><td>7.7<sup>a</sup></td><td>5.6<sup>b</sup></td><td>7.8<sup>w</sup></td><td>5.5<sup>yz</sup></td><td>8.2<sup>w</sup></td><td>5.8<sup>y</sup></td><td>6.5<sup>x</sup></td><td>5.3<sup>z</sup></td><td>0.04</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>DMI (g/kg BW)</td><td>33.1<sup>A</sup></td><td>31.3<sup>A</sup></td><td>24.9<sup>B</sup></td><td>35.7<sup>a</sup></td><td>25.0<sup>b</sup></td><td>40.3<sup>w</sup></td><td>26.0<sup>x</sup></td><td>37.0<sup>w</sup></td><td>25.7<sup>x</sup></td><td>27.4<sup>x</sup></td><td>22.4<sup>y</sup></td><td>0.22</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>OMI (kg/d)</td><td>5.6<sup>B</sup></td><td>6.0<sup>A</sup></td><td>5.2<sup>C</sup></td><td>6.6<sup>a</sup></td><td>4.8<sup>b</sup></td><td>6.6<sup>w</sup></td><td>4.7<sup>y</sup></td><td>7.0<sup>w</sup></td><td>5.0<sup>y</sup></td><td>5.7<sup>x</sup></td><td>4.7<sup>y</sup></td><td>0.04</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>OMI (g/kg BW)</td><td>28.3<sup>A</sup></td><td>26.6<sup>B</sup></td><td>21.9<sup>C</sup></td><td>30.5<sup>a</sup></td><td>21.4<sup>b</sup></td><td>34.4<sup>w</sup></td><td>22.1<sup>x</sup></td><td>31.4<sup>w</sup></td><td>21.8<sup>xy</sup></td><td>24.1<sup>x</sup></td><td>19.7<sup>y</sup></td><td>0.19</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>CPI (kg)</td><td>0.72<sup>A</sup></td><td>0.69<sup>A</sup></td><td>0.64<sup>B</sup></td><td>0.79<sup>a</sup></td><td>0.54<sup>b</sup></td><td>0.86</td><td>0.58</td><td>0.77</td><td>0.51</td><td>0.81</td><td>0.58</td><td>0.007</td><td>&lt;0.001</td><td>&lt;0.001</td><td>0.307</td></tr><tr><td>CPI (g/kg BW)</td><td>3.6<sup>A</sup></td><td>2.9<sup>B</sup></td><td>2.9<sup>B</sup></td><td>3.7<sup>a</sup></td><td>2.4<sup>b</sup></td><td>4.5<sup>w</sup></td><td>2.8<sup>xy</sup></td><td>3.5<sup>x</sup></td><td>2.3<sup>y</sup></td><td>3.4<sup>x</sup></td><td>2.4<sup>y</sup></td><td>0.03</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>NDFI (kg)</td><td>4.0<sup>A</sup></td><td>4.4<sup>A</sup></td><td>3.7<sup>B</sup></td><td>4.8<sup>a</sup></td><td>3.5<sup>b</sup></td><td>4.8<sup>w</sup></td><td>3.4<sup>y</sup></td><td>5.1<sup>w</sup></td><td>3.7<sup>xy</sup></td><td>4.0<sup>x</sup></td><td>3.3<sup>y</sup></td><td>0.03</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>NDFI (g/kg BW)</td><td>20.3<sup>A</sup></td><td>19.5<sup>A</sup></td><td>15.5<sup>B</sup></td><td>22.0<sup>a</sup></td><td>15.6<sup>b</sup></td><td>24.7<sup>w</sup></td><td>15.9<sup>xy</sup></td><td>23.0<sup>w</sup></td><td>16.1<sup>xy</sup></td><td>16.9<sup>x</sup></td><td>14.0<sup>y</sup></td><td>0.13</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>ADFI (kg)</td><td>2.2<sup>A</sup></td><td>2.5<sup>A</sup></td><td>2.0<sup>B</sup></td><td>2.7<sup>a</sup></td><td>2.0<sup>b</sup></td><td>2.6<sup>w</sup></td><td>1.9<sup>x</sup></td><td>2.9<sup>w</sup></td><td>2.1<sup>wx</sup></td><td>2.2<sup>wx</sup></td><td>1.9<sup>x</sup></td><td>0.02</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>ADFI (g/kg BW)</td><td>11.2<sup>A</sup></td><td>11.2<sup>A</sup></td><td>8.5<sup>B</sup></td><td>12.4<sup>a</sup></td><td>8.9<sup>b</sup></td><td>13.6<sup>w</sup></td><td>8.8<sup>xy</sup></td><td>13.2<sup>w</sup></td><td>9.3<sup>x</sup></td><td>9.2<sup>x</sup></td><td>7.9<sup>y</sup></td><td>0.08</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>GEI (MJ)</td><td>120.8<sup>B</sup></td><td>128.2<sup>A</sup></td><td>115.1<sup>C</sup></td><td>143.2<sup>a</sup></td><td>104.4<sup>b</sup></td><td>141.9<sup>w</sup></td><td>99.7<sup>y</sup></td><td>149.7<sup>w</sup></td><td>106.6<sup>y</sup></td><td>127.0<sup>x</sup></td><td>103.2<sup>y</sup></td><td>3.49</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>GEI (MJ/kg BW)</td><td>0.60<sup>A</sup></td><td>0.57<sup>B</sup></td><td>0.48<sup>C</sup></td><td>0.66<sup>a</sup></td><td>0.46<sup>b</sup></td><td>0.74<sup>w</sup></td><td>0.47<sup>z</sup></td><td>0.68<sup>x</sup></td><td>0.47<sup>z</sup></td><td>0.53<sup>y</sup></td><td>0.43<sup>z</sup></td><td>0.006</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr></tbody></table>

VeS: vegetative stage, ReS: reproductive stage, MaS: maturity stage, 4.5ING: animals fed at 4.5 % of BW, DM basis, 2.5ING: animals fed at 2.5 % of BW, DM basis; SEM: standard error of the mean.

DMI: dry matter intake, OMI: organic matter intake, CPI: crude protein intake, NDFI: neutral detergent fibre intake, ADFI: acid detergent fibre intake, GEI: gross energy intake, BW: body weight.

A,B,C Values with different superscripts within the same row differ significantly at P < 0.05: comparison between fodder growth stages.

a,b Values with different superscripts within the same row differ significantly at P < 0.05: comparison between fodder offered levels.

w,x,y,z Values with different superscripts within the same row differ significantly at P < 0.05: comparison based on the interaction between fodder growth stage and offered level.
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Dynamics of daily intake of natural green rangeland fodder (including bait distributed by GF) in Sudanese Fulani zebu bulls across different stages

VeS: vegetative stage, ReS: reproductive stage, MaS: maturity stage, 4.5ING: animals fed at 4.5 % of BW, DM basis, 2.5ING: animals fed at 2.5 % of BW, DM basis.</figcaption></figure>

<table><caption>**Table 3**

Chemical composition of fodder intake and refusals (without bait) in Sudanese Fulani zebu bulls across different fodder growth stages and feeding levels.</caption><thead><tr><th>Item</th><th></th><th></th><th>OM (%DM)</th><th>CP (%DM)</th><th>NDF (%DM)</th><th>ADF (%DM)</th><th>GE (MJ/kg DM)</th></tr></thead><tbody><tr><td rowspan="12">Fodder growth stage</td><td rowspan="4">VeS</td><td>Intake</td><td>85<sup>B</sup></td><td>11<sup>A</sup></td><td>61<sup>A</sup></td><td>34<sup>A</sup></td><td>18<sup>A</sup></td></tr><tr><td>Refusal</td><td>92<sup>A</sup></td><td>5<sup>B</sup></td><td>32<sup>B</sup></td><td>18<sup>B</sup></td><td>9<sup>B</sup></td></tr><tr><td>SEM</td><td>1.5</td><td>0.2</td><td>1.3</td><td>0.7</td><td>0.5</td></tr><tr><td>P-value</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td rowspan="4">ReS</td><td>Intake</td><td>85<sup>B</sup></td><td>9<sup>A</sup></td><td>63<sup>A</sup></td><td>36<sup>A</sup></td><td>18<sup>A</sup></td></tr><tr><td>Refusal</td><td>92<sup>A</sup></td><td>4<sup>B</sup></td><td>37<sup>B</sup></td><td>22<sup>B</sup></td><td>10<sup>B</sup></td></tr><tr><td>SEM</td><td>1.4</td><td>0.2</td><td>1.2</td><td>0.8</td><td>0.6</td></tr><tr><td>P-value</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td rowspan="4">MaS</td><td>Intake</td><td>88<sup>B</sup></td><td>12<sup>A</sup></td><td>62<sup>B</sup></td><td>34<sup>B</sup></td><td>19</td></tr><tr><td>Refusal</td><td>90<sup>A</sup></td><td>5<sup>B</sup></td><td>70<sup>A</sup></td><td>43<sup>A</sup></td><td>19</td></tr><tr><td>SEM</td><td>1.3</td><td>0.2</td><td>1.1</td><td>0.5</td><td>0.3</td></tr><tr><td>P-value</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td><td>0.200</td></tr><tr><td rowspan="12">Offered level</td><td rowspan="4">4.5ING</td><td>Intake</td><td>86</td><td>11<sup>a</sup></td><td>62<sup>b</sup></td><td>35<sup>b</sup></td><td>18</td></tr><tr><td>Refusal</td><td>86</td><td>7<sup>b</sup></td><td>66<sup>a</sup></td><td>39<sup>a</sup></td><td>18</td></tr><tr><td>SEM</td><td>1.0</td><td>0.2</td><td>0.9</td><td>0.5</td><td>0.2</td></tr><tr><td>P-value</td><td>0.237</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td><td>0.140</td></tr><tr><td rowspan="4">2.5ING</td><td>Intake</td><td>86<sup>b</sup></td><td>10<sup>a</sup></td><td>63<sup>a</sup></td><td>35<sup>a</sup></td><td>19<sup>A</sup></td></tr><tr><td>Refusal</td><td>97<sup>a</sup></td><td>2<sup>b</sup></td><td>21<sup>b</sup></td><td>13<sup>b</sup></td><td>5<sup>B</sup></td></tr><tr><td>SEM</td><td>1.3</td><td>0.4</td><td>1.2</td><td>0.8</td><td>0.4</td></tr><tr><td>P-value</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr></tbody></table>

OM: organic matter, DM: dry matter, CP: crude protein, NDF: neutral detergent fiber, ADF: acid detergent fiber, ADL: acid detergent lignin, GE: gross energy; SEM: standard error of the mean.

VeS: vegetative stage, ReS: reproductive stage, MaS: maturity stage, 4.5ING: animals fed at 4.5 % of BW, DM basis, 2.5ING: animals fed at 2.5 % of BW, DM basis.

<sup>A,B</sup> Values with different superscripts within the same row differ significantly at P < 0.05: comparison between fodder stages.

<sup>a,b</sup> Values with different superscripts within the same row differ significantly at P < 0.05: comparison between fodder offered levels.

### 3.3. Apparent digestibility

DM digestibility ranged from 59 to 76 %. No significant interaction was observed between fodder growth stage and feed allowance with respect to digestibility (P > 0.05; Table 4). Among the three fodder growth stages, the lowest digestibility values (P < 0.05) were recorded at MaS for all parameters except CP. No significant differences in digestibility were observed between the two levels of feed offered. Temporal trends indicated a decline in DM digestibility decreased from the onset of VeS, stability during ReS, and a further decrease at the

beginning of MaS (Fig. 2).

### 3.4. Average daily gain and feed conversion ratio

A significant interaction between fodder growth stage and feed allowance was observed for ADG (P < 0.05), whereas no interaction was found for FCR (P > 0.05; Table 5). The lowest ADG values were observed at MaS and under the 2.5ING treatment. Animals were 2–3 times more efficient at VeS compared to ReS and MaS. Additionally, those fed at 4.5ING demonstrated greater feed efficiency than those fed at 2.5ING.
<table><caption>**Table 4**

Apparent digestibility of natural green rangeland fodder intake (including bait distributed at GF) in Sudanese Fulani zebu bulls across different fodder growth stages.</caption><thead><tr><th rowspan="2">Items</th><th colspan="3">Fodder growth stage</th><th colspan="3">Feeding level</th><th colspan="3">Fodder growth stage * Feeding level</th><th colspan="3">SEM</th></tr><tr><th>VeS</th><th>ReS</th><th>MaS</th><th>4.5ING</th><th>2.5ING</th><th>VeS * 4.5ING</th><th>VeS * 2.5ING</th><th>ReS * 4.5ING</th><th>ReS * 2.5ING</th><th>MaS * 4.5ING</th><th>MaS * 2.5ING</th><th>P-value</th></tr></thead><tbody><tr><td>DM (%DMI)</td><td>74.5<sup>a</sup></td><td>72.4<sup>a</sup></td><td>65.3<sup>b</sup></td><td>72.5</td><td>70.1</td><td>76.0</td><td>73.0</td><td>73.5</td><td>71.3</td><td>67.4</td><td>63.3</td><td>4.12</td></tr><tr><td>OM (%OMI)</td><td>76.0<sup>a</sup></td><td>73.5<sup>b</sup></td><td>66.9<sup>c</sup></td><td>73.9</td><td>71.2</td><td>76.9</td><td>74.9</td><td>74.6</td><td>72.4</td><td>68.8</td><td>64.9</td><td>4.20</td></tr><tr><td>CP (%CPI)</td><td>74.7<sup>a</sup></td><td>70.3<sup>a</sup></td><td>74.0<sup>a</sup></td><td>73.0</td><td>71.0</td><td>75.5</td><td>73.9</td><td>71.4</td><td>69.3</td><td>75.0</td><td>73.0</td><td>0.74</td></tr><tr><td>NDF (%NDFI)</td><td>76.9<sup>a</sup></td><td>75.1<sup>a</sup></td><td>67.0<sup>b</sup></td><td>74.9</td><td>72.5</td><td>77.6</td><td>76.2</td><td>76.0</td><td>74.3</td><td>68.9</td><td>65.1</td><td>3.08</td></tr><tr><td>ADF (%ADF)</td><td>73.3<sup>a</sup></td><td>72.3<sup>a</sup></td><td>62.3<sup>a</sup></td><td>71.7</td><td>69.1</td><td>74.7</td><td>71.9</td><td>73.2</td><td>71.5</td><td>63.7</td><td>60.9</td><td>2.03</td></tr><tr><td>DEI (MJ/d)</td><td>91.8<sup>a</sup></td><td>94.9<sup>a</sup></td><td>79.4<sup>b</sup></td><td>107.4<sup>a</sup></td><td>75.2<sup>b</sup></td><td>109.3<sup>a</sup></td><td>74.8<sup>a</sup></td><td>112.3<sup>a</sup></td><td>77.8<sup>a</sup></td><td>88.9<sup>a</sup></td><td>69.1<sup>a</sup></td><td>2.08</td></tr><tr><td>EE (DEI/GEI, MJ/ML)</td><td>76.5<sup>a</sup></td><td>74.1<sup>b</sup></td><td>69.0<sup>c</sup></td><td>74.7<sup>a</sup></td><td>72.3<sup>b</sup></td><td>77.0</td><td>75.1</td><td>74.9</td><td>73.3</td><td>69.8</td><td>68.2</td><td>0.24</td></tr></tbody></table>

VeS: vegetative stage, ReS: reproductive stage, MaS: maturity stage, 4.5ING: animals fed at 4.5 % of BW, DM basis, 2.5ING: animals fed at 2.5 % of BW, DM basis; SEM: standard error of the mean.

DM: dry matter, DMI: dry matter intake, OM: organic matter, OMI: organic matter intake, CP: crude protein, CPI: crude protein intake, NDF: neutral detergent fiber, NDFI: neutral detergent fibre intake, ADF: acid detergent fiber, ADFI: acid detergent fibre intake, EE: energy efficiency, GEI: gross energy intake.

A,B,C Values with different superscripts within the same row differ significantly at P < 0.05; comparison between fodder stages.

a,b Values with different superscripts within the same row differ significantly at P < 0.05; comparison between fodder offered levels.

The highest ADG was recorded in the 4.5ING treatment during VeS. The BW trajectory over the study period is illustrated in Fig. 3.

### 3.5. Enteric methane emissions

Average eCH₄ production per animal ranged from 58.21 to 204.32 g/d with an average of 118.04 g/d, corresponding to 0.52 g/kg BW and 18.06 g/kg DM intake. Significant interactions between fodder growth stage and feed allowance were observed for most eCH₄ emission metrics (production, yield, and intensity; P < 0.05; Table 6), whereas no interaction was found for Ym (%GEI; P > 0.05). Significant differences in eCH₄ emissions (g/kg BW) were observed across fodder growth stages. Compared to 2.5ING, 4.5ING treatment induced 19 % more (P < 0.05) eCH₄ emissions (g/kg BW), yet yielded the lowest (P < 0.05) eCH₄ intensity (g/kg ADG). When expressed per gram of protein produced (g/g ePCMO), eCH₄ intensity doubled and tripled at ReS and MaS, respectively, relative to VeS (P < 0.001). eCH₄ yield (g/kg DM intake) and intensity were lowest (P < 0.05) at VeS and highest at MaS. While eCH₄ yield (g/kg DM intake) remained stable during VeS and ReS, it increased markedly during MaS (Fig. 4). The lowest eCH₄ yield and intensity were observed in the 4.5ING treatment during VeS.

### 4. Discussion

Given that natural rangeland fodder constitutes the main feed resource for pastoral and agropastoral systems in SSA, understanding its seasonal variability is critical for optimizing livestock productivity and mitigating associated environmental impacts. In particular, characterizing both inter- and intra-seasonal fluctuations in feed intake, digestibility, and eCH₄ emissions is essential for addressing the uncertainties surrounding emission dynamics during the wet season. Such insights may inform more targeted mitigation strategies and enhance the sustainability of livestock systems year-round.

#### 4.1. Rangeland fodder quality in the wet season

The rangeland fodder evaluated in this study was predominantly composed of *Andropogon gayanus* Kunth, a species widely representative of the Sudanian zone. Although its botanical composition was consistent with that reported by Gbenou et al. [5] in the study area, notable differences were observed in its chemical composition, particularly in CP, NDF, and ADF contents. Whereas previous studies emphasized broader seasonal trends, the present study focused specifically on intra-seasonal variations within the wet season. The findings revealed significant shifts in fodder quality across growth stages, underscoring the dynamic nature of forage nutritive value even within a single season.

At the onset of the wet season (corresponding to VeS), rangeland fodder exhibited high CP content (109 g/kg DM) and relatively low fiber fractions, NDF (616 g/kg DM) and ADF (340.6 g/kg DM). These characteristics contributed to elevated digestibility values for DM, OM, CP, NDF, and ADF, consistent with findings by Xia et al. [29], who demonstrated that increased dietary CP enhances digestibility. The fodder quality at VeS aligns with values reported by Dieng et al. [30] for one-week regrowth of pure *A. gayanus*. However, it remains lower than for the nutritional profile of fodder harvested in dry tropical regions (CP: 136 g/kg DM, ADF: 332 g/kg DM) as documented by INRA [31]. Notably, the NDF contents (667 g/kg DM) reported by INRA appears inconsistent with expected fiber relationships, as NDF typically exceeds ADF, particularly in CP-rich forages [32]. Such discrepancies may reflect regional differences in species composition, abiotic stressors, and adaptive plant responses [33].

During the mid-wet season (corresponding to ReS), CP contents decreased by approximately 18 %, while NDF and ADF contents increased significantly. This shift coincided with a marked reduction in OM and CP digestibility, likely attributable to plant maturation and the onset of senescence, as described by Sbrissia et al. [34]. The emergence
<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Dynamics of dry matter apparent digestibility of natural green rangeland fodder intake (including bait distributed by GF) in Sudanese Fulani zebu bulls across different stages</figcaption></figure>

VeS: vegetative stage, ReS: reproductive stage, MaS: maturity stage, 4.5ING: animals fed at 4.5 % of BW, DM basis, 2.5ING: animals fed at 2.5 % of BW, DM basis.

of inflorescences during this stage typically signals a decline in forage quality. A comparison between ReS values (CP: 89.5 g/kg DM, NDF: 630.6 g/kg DM) and those reported by INRA [31] for dry tropical rangelands (CP: 128 g/kg DM, NDF: 562 g/kg DM) further illustrates this decline. Variations may also stem from edaphic conditions and nutrient recycling via animal excreta, which influence plant nutrient dynamics.

At the end of the wet season (corresponding to MaS), an unexpected increase in CP content was observed, reaching levels comparable to VeS. This contrast with Müller et al. [35], who reported a consistent decline in forage quality with advancing plant maturity. The elevated CP levels at MaS can be attributed to late-season regrowth stimulated by residual rainfall, a phenomenon known to enhance protein content [36]. Despite this regrowth, fiber concentrations (NDF and ADF) remained high, and digestibility of DM and OM declined relative to earlier stages, reaffirming the overall reduction in nutritional value. High fiber content is generally associated with lower digestibility, and without the observed regrowth, the fodder quality at MaS would likely resemble that reported by Gbenou et al. [5], who documented notably poor nutritional profiles (CP: 66 g/kg DM, NDF: 660 g/kg DM and ADF: 398 g/kg DM).

The decline in digestibility parameters at MaS, particularly DM, OM, NDF and ADF digestibility, is consistent with the progression of plant maturity and senescence [37]. On average, the wet-season fodder quality (CP: 101 g/kg DM, NDF: 632 g/kg DM and ADF: 356 g/kg DM) aligns with values reported by Dieng et al. [30] for five-week-old *A. gayanus* in its first growth cycle. However, it remains inferior to the nutritional composition (CP: 194 g/kg DM, NDF: 572 g/kg DM and ADF: 391 g/kg DM) reported by Ayantunde et al. [38] for grass-dominated pastures in Niger. The absence of detailed information on plant maturity and species composition in those studies may account for the observed discrepancies.

## 4.2. Rangeland fodder intake by zebu bulls

Forage intake in ruminants is influenced by multiple factors, notably

feeding behavior [38,39]. Unlike grazing-based studies, this barn-based experiment did not account for behavioral variables such as locomotion and foraging effort. The highest DMI (33 g/kg BW) was recorded at VeS, coinciding with greater DM digestibility, while the lowest value (25 g/kg BW) was recorded at MaS, reflecting increased fiber content and reduced digestibility. This intake pattern aligns with the progressive increase in NDF and ADF contents from VeS to MaS. Comparable seasonal trends were observed by Ayantunde et al. [38] in Niger, where Azawak bulls (*Bos indicus*) grazing annual grasses showed declining intake from early to late dry season. It is well established that ruminants consume more low-fiber forages than those fiber-rich alternatives [40].

Across growth stages, DM intake values in this study ranged within the 20–30 g/kg BW recommended by Boudet and Rivière [41] for tropical cattle, yet exceeded the 17–20 g/kg BW reported in the wet season by Assouma et al. [42] for lighter grazing steers (115–140 kg) during the wet season in Senegal. These findings suggest that the conventional reference value of 2.5 % BW proposed by Rivière [43] may underestimate actual intake capacity, particularly under wet-season conditions, potentially constraining productivity. The average DM intake also surpassed the 22.3 g/kg BW reported by Gbenou et al. [5], when steers were fed rangeland fodder at 2.3 % BW. This discrepancy likely reflects differences in fodder quality and restricted feed allowance.

Fodder availability had a pronounced effect on intake: bulls offered 4.5 % BW consumed 43 % more than those restricted to 2.5 % BW, corroborating earlier findings by Prezotto et al. [44] that greater availability enhances consumption. The DM intake value (25 g/kg BW) at 2.5ING closely matched the 22.3 g/kg BW reported by Gbenou et al. [5], reinforcing the impact of limited provision. Refusals further illustrate feeding dynamics. At 4.5ING, refusals reached 21 %, indicating near ad libitum conditions, while near-zero refusals at 2.5ING confirmed restricted feeding. The 4.5ING refusal rate exceeded the 10 % threshold suggested by Boval et al. [45] to ensure high fodder allowance access without excessive selection. Identifying an optimal feeding level that
<table><caption>**Table 5**
Average daily gain and feed conversion ratio of Sudanese Fulani zebu bulls fed with natural green rangeland fodder across different stages.</caption><thead><tr><th rowspan="2">Item</th><th colspan="3">Fodder growth stage</th><th colspan="3">Feeding level</th><th colspan="3">Fodder growth stage * Feeding level</th><th colspan="3">SEM</th><th colspan="3">P-value</th></tr><tr><th>VeS</th><th>ReS</th><th>MaS</th><th>4.5ING</th><th>2.5ING</th><th>2.5ING</th><th>VeS * 4.5ING</th><th>ReS * 2.5ING</th><th>ReS * 4.5ING</th><th>MaS * 4.5ING</th><th>MaS * 2.5ING</th><th>Fodder growth stage</th><th>Feeding level</th><th>Fodder growth stage * Feeding level</th></tr></thead><tbody><tr><td>Initial weight (kg)</td><td>194.6<sup>c</sup></td><td>211.3<sup>b</sup></td><td>234.8<sup>a</sup></td><td>185.0<sup>b</sup></td><td>204.2<sup>a</sup></td><td>184.7<sup>a</sup></td><td>204.2<sup>y</sup></td><td>202.4<sup>a</sup></td><td>220.1<sup>x</sup></td><td>234.8<sup>w</sup></td><td>234.8<sup>w</sup></td><td>4.43</td><td>&lt;0.001</td><td>0.016</td><td>0.034</td></tr><tr><td>Final weight (kg)</td><td>211.3<sup>c</sup></td><td>234.8<sup>b</sup></td><td>241.0<sup>a</sup></td><td>243.1<sup>a</sup></td><td>238.8<sup>b</sup></td><td>202.4<sup>x</sup></td><td>220.1<sup>y</sup></td><td>234.8<sup>x</sup></td><td>234.8<sup>x</sup></td><td>243.1<sup>w</sup></td><td>238.8<sup>w</sup></td><td>8.12</td><td>0.004</td><td>0.039</td><td>0.001</td></tr><tr><td>ADG (g/d)</td><td>795.2<sup>a</sup></td><td>420.0<sup>b</sup></td><td>294.3<sup>c</sup></td><td>592.8<sup>b</sup></td><td>353.0<sup>b</sup></td><td>842.8<sup>w</sup></td><td>757.1<sup>w</sup></td><td>578.6<sup>x</sup></td><td>262.5<sup>x</sup></td><td>395.2<sup>y</sup></td><td>190.5<sup>x</sup></td><td>12.52</td><td>&lt;0.001</td><td>0.027</td><td>0.020</td></tr><tr><td>ePCMO (g/d)</td><td>58.4<sup>a</sup></td><td>30.8<sup>b</sup></td><td>21.6<sup>c</sup></td><td>43.5<sup>z</sup></td><td>25.9<sup>b</sup></td><td>61.9<sup>w</sup></td><td>55.6<sup>w</sup></td><td>42.5<sup>x</sup></td><td>19.3<sup>x</sup></td><td>29.0<sup>y</sup></td><td>14.0<sup>x</sup></td><td>3.89</td><td>&lt;0.001</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>FCR (kg DMI/kg ADG)</td><td>8.3<sup>c</sup></td><td>16.7<sup>b</sup></td><td>20.0<sup>a</sup></td><td>13.0<sup>b</sup></td><td>16.0<sup>b</sup></td><td>9.3</td><td>7.3</td><td>14.2</td><td>22.1</td><td>16.4</td><td>27.8</td><td>2.34</td><td>&lt;0.001</td><td>0.048</td><td>0.055</td></tr></tbody></table>

VeS: vegetative stage, ReS: reproductive stage, MaS: maturity stage, 4.5ING: animals fed at 4.5 % of BW, DM basis, 2.5ING: animals fed at 2.5 % of BW, DM basis; SEM: standard error of the mean.

ADG: average daily gain, ePCMO: protein-corrected-meat output, FCR: feed conversion ratio, DMI: dry matter intake.

A,B,C Values with different superscripts within the same row differ significantly at *P* < 0.05; comparison between fodder stages.

a,b Values with different superscripts within the same row differ significantly at *P* < 0.05; comparison between fodder offered levels.

w,x,y,z Values with different superscripts within the same row differ significantly at *P* < 0.05; comparison based on the interaction between fodder growth stage and offered level.

minimizes waste while maintaining this threshold is a key objective for precision feeding strategies. Such optimization is challenged by the need to standardize botanical composition across fodder growth stages and seasonal variations. Notably, intake samples consistently contained higher CP than refusals, as also observed by Gbenou et al. [5]. At MaS, refusals were richer in fiber due to lignification, while at 4.5ING, lower fiber contents in refusals reflected selective feeding behavior favoring higher-quality components. In contrast, animals at the 2.5ING level consume nearly all offered forage, limiting selectivity.

### 4.3. Average daily gain and feed conversion ratio in zebu bulls

Weight gain in cattle is closely linked to feed intake, its digestibility, initial BW, and the animal's efficiency in converting feed into body mass [46]. The FCR, defined as the quantity of feed required to produce a unit of weight gain, serves as key indicator of feed efficiency. Evaluating both ADG and FCR is essential not only for assessing nutritional performance but also for enhancing livestock productivity and profitability, particularly in SSA where livestock plays an important role in food security.

In the current study, both ADG and FCR varied significantly across rangeland fodder growth stages and between feed supplying levels. The VeS was characterized by the highest CP content, which coincided with the highest ADG and the lowest FCR. In contrast, the ReS exhibited the lowest CP content, a significant reduction in ADG and a FCR value nearly twice that of VeS, indicating less efficient feed utilization. Although CP content increased again at MaS, DMI was lower than during ReS, and ADG continued to decline, resulting in the highest FCR. These findings suggest that fodder CP content alone is insufficient to sustain animal performance when intake and digestibility are constrained by advanced plant maturity. Despite the importance of these metrics, few studies in Africa have examined cattle fattening performance and feed conversion in depth. These findings revealed a positive correlation between ADG and DM intake (g/kg BW), consistent with results from Archer and Bergh [47] who studied young beef cattle (239–254 kg) fed a pelleted diet in South Africa. In contrast, ADG was negatively associated with fiber content (NDF and ADF), both in offered and consumed fodder, supporting observations by Malole et al. [48] in Tanzania, where on indigenous beef cattle were fed natural pasture and cottonseed by-products (hulls and cake). Digestible DM intake also showed a positive relationship with ADG, as previously reported by Boval et al. [49] in tropical cattle breeds.

Comparative studies on African cattle breeds often report lower ADG values than those observed in this study. For instance, Gbenou et al. [50] reported an ADG range of 123–255 g/day in 161 kg Gir x Borgou crossbred steers grazing *Panicum maximum* C1 and supplemented with sorghum brewer's during the dry season in Benin. Smith et al. [51] found ADGs ranging from 68 to 101 g/d (7.6–11.3 kg over 16 weeks) in 292 kg Ogaden bulls grazing natural pasture in Ethiopia. In contrast, higher ADG values have been reported: Ayantunde et al. [38] reported ADG values ranging from 368 to 539 g/d in Azawak bulls during the wet season, while Fynn and O'Connor [52] recorded 227–669 g/day in Brahman-crossbred cattle grazing perennial grasses in South Africa. Similarly, Carvalheira et al. [53] reported 245–298 g/d in Mozambique under natural grazing conditions. These variations are largely attributed to breed differences [54,55], birth weight [56], feeding strategies [48], and phenotypic variability [57], as well as sex and animal category [53].

Significant differences in ADG were observed between the two fodder allowance levels. Bulls fed at 2.5 % BW exhibited lower ADGs due to restricted intake, which limited growth potential. These findings align with those of Boval et al. [49] and Prezotto et al. [44] who demonstrated that herbage allowance directly influences ADG. Fynn and O'Connor [52] also highlighted the role of stocking rate and rainfall in shaping rangeland dynamics and cattle performance. Notably, cattle were 2–3 times more efficient during VeS than at later fodder stages, suggesting possible compensatory growth. Similarly, animals fed at 4.5 % BW were more efficient than those at 2.5 % BW.
<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Dynamics of body weight of Sudanese Fulani zebu bulls fed with natural green rangeland fodder across different stages
VeS: vegetative stage, ReS: reproductive stage, MaS: maturity stage, 4.5ING: animals fed at 4.5 % of BW, DM basis, 2.5ING: animals fed at 2.5 % of BW, DM basis.</figcaption></figure>

A phenotypic relationship among DM intake, ADG, and FCR was evident, echoing findings by Smith et al. (2010). ADG was positively correlated with DM intake and negatively with FCR across fodder stages and feed levels, consistent with results from Siddque et al. [54] and Boval et al. [49]. The FCR values observed in this study fall within the range of 9.48–19.7 reported by Siddque et al. [54] for indigenous and crossbred cattle. Lower FCRs (7.3–10) were reported by Prezotto et al. [44] and Polizel et al. [55], while Gbenou et al. [50] documented higher values (20–35), likely reflecting differences in breed and feeding practices.

## 4.4. Enteric methane emissions in zebu bulls

Given the intra-seasonal variability of livestock GHG emissions, particularly eCH₄, accurate seasonal and annual emission factors are essential for West Africa. Building on the methodology of Gbenou et al. [5,15], this study incorporated feeding behavior patterns typical of pasture-based systems. While conducted in a controlled barn setting, future replication under grazing conditions would allow consideration of additional environmental and behavioral parameters, such as animal movement and microclimate effects. The study did not examine gut microbiota composition or volatile fatty acid concentrations, both of which play a crucial role in eCH₄ formation. This represents a limitation of the current research and will be addressed in future studies. Nevertheless, the present experiment involved a substantially higher number of measurement visits compared with those reported by Hristov et al. [58], Manafiazar et al. [16], and Gbenou et al. [5,15], thereby strengthening the reliability of daily eCH₄ estimates and enabling more accurate calculations of emission intensity relative to animal productivity.

### 4.4.1. Emission dynamics across fodder growth stages

During the wet season, eCH₄ emissions (g/kg BW) varied significantly across fodder growth stages. The highest emissions were recorded at the VeS, driven by elevated intake and digestibility. Conversely, the

lowest emissions occurred at the MaS, corresponding to reduced NDF intake. These findings align with Alvarado-Bolovich et al. [59], who reported positive correlations between intake, digestibility, and eCH₄ output. Emissions at ReS and MaS were lower than those observed during the cold dry season in Gbenou et al. [5], underscoring the superior nutritional quality of wet-season rangeland fodder. A positive relationship was also found between eCH₄ emissions (g/kg BW) and GEI (g/kg BW), although this did not significantly affect the proportion of GEI lost as eCH₄ (Ym).

### 4.4.2. Influence of intake level

Average eCH₄ production was 0.58 g/kg BW for bulls fed at 4.5 % BW and 0.47 g/kg BW for those at 2.5 % BW, reflecting differences in DM and NDF intake. The latter value corroborates Gbenou et al. [5], who reported similar emissions in steers fed at 2.3 % of BW. Across the wet season, bulls emitted an average of 118.04 g/d, (0.52 g/kg BW, 18.06 g/kg DM intake, and 19.9 kg/Tropical Livestock Unit). When extrapolated over 151 days, this yields 17.8 kg/head, slightly below the 21.5 kg/head calculated using IPCC Tier 1 (2019) default values for bulls. The IPCC Tier 2 default value is 21 g/kg DM intake per day for non-dairy cattle fed high-quality forage-based diets (>75 % with digestibility between 62 and 71 %) exceeds the value observed in this study, despite our forage digestibility ranging between 65 and 74 %.

### 4.4.3. Comparative studies and regional context

Yassegoungbe et al. [11] reported lower emissions (0.46 g/kg BW, 20.6 g/kg DM intake) in 351 kg bulls grazing natural pasture in Benin. Similarly, Ndao et al. [10] found 0.26 g/kg BW (21.5 g/kg DM intake) in 250 kg N'dama bulls in Senegal. These discrepancies are likely due to differences in measurement techniques, animal weight, forage quality [15], and physiological status. Few studies have reported in vivo eCH₄ measurements during the wet season in Africa. Gbenou et al. [5] used the GF system to measure 0.45 g/kg BW (20.5 g/kg DM intake) in 130 kg steers in Burkina Faso. Mapfumo et al. [60] recorded higher values (0.7–0.8 g/kg BW; 26–30 g/kg DM intake) using a laser methane
<table><caption>**Table 6**
Emissions of eCH₄ by Sudanese Fulani zebu bulls fed natural green rangeland fodder (including bait distributed by GF) across different fodder growth stages.</caption><thead><tr><th rowspan="2">Item</th><th colspan="3">Fodder growth stage</th><th colspan="3">Feeding level</th><th colspan="3">Fodder growth stage * Feeding level</th><th colspan="3">SEM</th><th colspan="3">P-value</th></tr><tr><th>VeS</th><th>ReS</th><th>MaS</th><th>4.5ING</th><th>2.5ING</th><th>VeS * 4.5ING</th><th>VeS * 2.5ING</th><th>ReS * 4.5ING</th><th>ReS * 2.5ING</th><th>MaS * 4.5ING</th><th>MaS * 2.5ING</th><th>Fodder growth stage</th><th>Offered level</th><th>Fodder growth stage * Feeding level</th></tr></thead><tbody><tr><td>CO₂ (g/d)</td><td>2917<sup>b</sup></td><td>3035<sup>AB</sup></td><td>3159<sup>A</sup></td><td>3156<sup>a</sup></td><td>2934<sup>b</sup></td><td>3071<sup>x</sup></td><td>2678<sup>y</sup></td><td>3253<sup>wx</sup></td><td>2733<sup>xy</sup></td><td>3310<sup>w</sup></td><td>2953<sup>x</sup></td><td>12.3</td><td>0.001</td><td>&lt;0.001</td></tr><tr><td>eCH₄ (g/d)</td><td>109.2</td><td>116.0</td><td>121.3</td><td>126.1<sup>a</sup></td><td>105.2<sup>b</sup></td><td>118.7</td><td>99.7</td><td>127.6</td><td>104.4</td><td>129.6</td><td>113.1</td><td>0.04</td><td>0.061</td><td>0.069</td></tr><tr><td>eCH₄ (g/kg BW)</td><td>0.54<sup>A</sup></td><td>0.51<sup>B</sup></td><td>0.50<sup>B</sup></td><td>0.58<sup>a</sup></td><td>0.47<sup>b</sup></td><td>0.62<sup>w</sup></td><td>0.47<sup>x</sup></td><td>0.58<sup>x</sup></td><td>0.46<sup>x</sup></td><td>0.54<sup>wx</sup></td><td>0.48<sup>x</sup></td><td>0.045</td><td>0.002</td><td>&lt;0.001</td></tr><tr><td>eCH₄ (g/kg DMI)</td><td>16.8<sup>b</sup></td><td>16.8<sup>b</sup></td><td>21.1<sup>a</sup></td><td>16.7</td><td>18.8</td><td>15.4<sup>a</sup></td><td>18.2<sup>x</sup></td><td>15.7<sup>y</sup></td><td>17.9<sup>x</sup></td><td>20.6<sup>w</sup></td><td>21.6<sup>w</sup></td><td>0.00</td><td>&lt;0.001</td><td>0.302</td></tr><tr><td>eCH₄ (g/kg DMI)</td><td>22.9<sup>b</sup></td><td>23.4<sup>b</sup></td><td>33.8<sup>a</sup></td><td>23.7<sup>b</sup></td><td>27.3<sup>a</sup></td><td>20.6</td><td>25.1</td><td>21.7</td><td>25.2</td><td>32.6</td><td>34.9</td><td>0.03</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>eCH₄ (g/kg OMI)</td><td>19.8<sup>b</sup></td><td>19.8<sup>b</sup></td><td>24.0<sup>a</sup></td><td>19.5</td><td>21.8</td><td>18.1<sup>a</sup></td><td>21.4<sup>wx</sup></td><td>18.6<sup>x</sup></td><td>21.0<sup>wx</sup></td><td>23.4<sup>w</sup></td><td>24.6<sup>w</sup></td><td>0.02</td><td>&lt;0.001</td><td>0.057</td></tr><tr><td>eCH₄ (g/kg DMI)</td><td>26.5<sup>b</sup></td><td>27.2<sup>b</sup></td><td>37.2<sup>a</sup></td><td>27.2<sup>b</sup></td><td>31.2<sup>a</sup></td><td>23.9</td><td>29.0</td><td>25.2</td><td>29.2</td><td>35.5</td><td>38.9</td><td>0.00</td><td>&lt;0.001</td><td>0.021</td></tr><tr><td>eCH₄ (g/kg ADG)</td><td>136.5<sup>c</sup></td><td>276.0<sup>b</sup></td><td>404.3<sup>a</sup></td><td>212.7<sup>b</sup></td><td>298.0<sup>a</sup></td><td>140.8<sup>x</sup></td><td>131.7<sup>y</sup></td><td>220.5<sup>y</sup></td><td>397.7<sup>x</sup></td><td>327.9<sup>x</sup></td><td>593.7<sup>w</sup></td><td>3.65</td><td>&lt;0.001</td><td>0.536</td></tr><tr><td>eCH₄ (g/kg OMI)</td><td>1.9<sup>c</sup></td><td>3.8<sup>b</sup></td><td>5.6<sup>a</sup></td><td>2.9<sup>b</sup></td><td>4.1<sup>a</sup></td><td>1.9<sup>x</sup></td><td>1.8<sup>y</sup></td><td>3.0<sup>y</sup></td><td>5.4<sup>x</sup></td><td>4.5<sup>xy</sup></td><td>8.1<sup>w</sup></td><td>0.10</td><td>&lt;0.001</td><td>&lt;0.001</td></tr><tr><td>Ym (% GFI)</td><td>5.1</td><td>5.1</td><td>6.0</td><td>5.0</td><td>5.6</td><td>4.7</td><td>5.6</td><td>4.8</td><td>5.4</td><td>5.9</td><td>6.2</td><td>0.03</td><td>0.08</td><td>0.103</td></tr></tbody></table>

VeS: vegetative stage, ReS: reproductive stage, MaS: maturity stage, 4.5ING: animals fed at 4.5% of BW, DM basis, 2.5ING: animals fed at 2.5% of BW, DM basis; SEM: standard error of the mean.

eCH₄: enteric methane, BW: body weight, DMI: dry matter intake, dDMI: digestible dry matter intake, OMI: organic matter intake, DMI: digestible organic matter intake, ADG: average daily gain, ePCMO: protein-corrected-meat output, GFI: gross energy intake.

A,B,C Values with different superscripts within the same row differ significantly at *P* < 0.05; comparison between fodder stages.

a,b Values with different superscripts within the same row differ significantly at *P* < 0.05; comparison between fodder offered levels.

w,x,y,z Values with different superscripts within the same row differ significantly at *P* < 0.05; comparison based on the interaction between fodder growth stage and offered level.

detector in 450 kg Boran and Nguni cows in South Africa. These differences may stem from variations in BW, physiological status [61], and measurement methods [62]. There is a pressing need for more *in vivo* eCH₄ data across diverse livestock systems in West Africa to improve GHG inventories and inform mitigation strategies.

### 4.4.4. Methane efficiency and feed quality

Significant differences in eCH₄ efficiency were observed across treatments. eCH₄ emission intensities ranged from 137 g/kg ADG at VeS to 400 g/kg ADG at MaS, with intermediate values at ReS. These results highlight the role of forage digestibility and nutrient composition in shaping microbial fermentation and eCH₄ emissions [63]. Bulls at VeS, fed nutrient-rich early wet-season fodder, achieved higher ADG and lower eCH₄ intensity. This supports findings by Van Lingen et al. [64], who reported a negative correlation between feed quality and eCH₄ intensity. In contrast, MaS fodder, characterized by high lignin and fiber, resulted in the highest emission intensity. These values exceed those reported by Van Lingen et al. [64] for cattle diets with ≥25% and ≤18% forage (5.08 and 4.68 g/kg ADG, respectively), reflecting differences in production systems.

### 4.4.5. Synergistic effects of intake and fodder stage

Intake level further modulated eCH₄ intensity. Bulls fed at 4.5% BW emitted less eCH₄ per unit of weight gain (200 g/kg ADG) than those at 2.5% BW (300 g/kg ADG), consistent with Niu et al. [65], who showed that higher intake promotes growth and reduces maintenance energy losses. Interestingly, the interaction between fodder stage and intake level was synergistic: VeS combined with 4.5ING yielded the best efficiency, while MaS with 2.5ING resulted in the poorest. This dual leverage, enhancing both feed quality and quantity, is especially relevant for low-input systems where animals underperform relative to their genetic potential.

### 4.5. Limitations of the study

Despite the important insights it provides into intra-seasonal dynamics of fodder quality, animal performance, and eCH₄ emissions, this study has several limitations that should be considered when interpreting the results. The experiment was conducted with a relatively small number of animals (n = 10), with five animals per feeding level. Although the long duration of the trial (98 days) and the repeated-measures design enhanced the robustness of the dataset and statistical power, caution is required when extrapolating the findings to larger herds or other production systems. Efforts will be made, where possible, to include a larger number of animals in future studies.

The study was carried out under controlled housing conditions, using rangeland fodder harvested and distributed daily, which allowed precise measurements of intake, digestibility, and gaseous emissions. However, these conditions do not fully reflect the complexity of pastoral and agropastoral systems, where animal movement, selective grazing, open grazing practices, pasture heterogeneity, and microclimatic conditions can influence intake patterns, energy expenditure, and eCH₄ emissions. Consequently, the emission levels and zootechnical performance observed in this study may differ under free-grazing conditions. This aspect also represents an important avenue for future research, particularly to collect data directly under grazing conditions across different fodder growth stages.

The eCH₄ emissions were measured using the GreenFeed® system, which provides reliable spot measurements but does not allow continuous 24 h monitoring. Although the high number of daily visits per animal improves the reliability of emission estimates, short-term fluctuations in eCH₄ production may not have been fully captured. In addition, the study did not use a continuous data collection system at regular time intervals, nor did it cover all hours of the day. Information spanning the full 24 h cycle could be highly valuable in future research to better understand diurnal variations and interactions between fodder
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Dynamics of enteric methane yield of Sudanese Fulani zebu bulls fed with natural green rangeland fodder across different stages
VeS: vegetative stage, ReS: reproductive stage, MaS: maturity stage, 4.5ING: animals fed at 4.5 % of BW, DM basis, 2.5ING: animals fed at 2.5 % of BW, DM basis.</figcaption></figure>

growth stage and feed allowance. Finally, the study did not include
analyses of the rumen microbial community or fermentation end-
products (such as volatile fatty acids), which are key determinants of
eCH₄ production. The absence of these measurements limits the ability
to directly link observed variations in eCH₄ emissions to the underlying
ruminal mechanisms.

4.6. Implications and future directions

This study offers a unique dataset of daily eCH₄ emissions over 98
days, capturing the full wet-season growth cycle of natural rangeland
fodder. Unlike short-term studies [5,15,17], continuous monitoring
revealed nuanced variations in forage quality, intake, and digestibility.
Although conducted in barn setting, the use of natural rangeland fodder
provides realistic insights into grazing dynamics. These findings also
reinforce the utility of applying a 10 % refusal threshold to define high
fodder allowance feeding and to limit selective intake [45]. Providing
forage above maintenance levels enabled voluntary selection and vari-
able intake, bridging the gap between controlled experiments and field
conditions.

Future research should explore ruminal microbiota to elucidate mi-
crobial drivers of the observed dynamics of eCH₄ emissions. Extending
this approach into the dry season would offer a comprehensive view of
seasonal emissions trajectories. Such efforts, combined with expanding
datasets and targeted research focused in African contexts, will enhance
predictive models and refine emission factors and models for tropical
rangeland systems.

5. Conclusion

This study demonstrates that the growth stage of rangeland fodder
significantly influences feed intake, digestibility, average daily gain,
feed conversion ratio, and enteric methane emissions in cattle during the
wet season in West Africa. Feeding cattle during fodder's vegetative
stage enhances digestibility and reduces methane emissions. Moreover,

offering fodder at 4.5 % of body weight improves animal performance
without increasing total methane output, while reducing methane in-
tensity. Interesting interactions were observed between the fodder
growth stage and feed allowance. The combination of vegetative stage
and a feed allowance equivalent to 4.5 % of body weight resulted in the
best animal performance, accompanied by the lowest methane yield and
intensity. These findings underscore the importance of synchronizing
feeding strategies with fodder growth stages to optimize productivity
and minimize negative environmental impacts in extensive livestock
systems. To enhance livestock production, emphasis should be placed on
early-stage forage and its availability during the wet season. This
strategy supports higher animal performance while simultaneously
reducing methane emissions, thereby contributing to more sustainable
and climate-smart livestock systems in the region.

CRediT authorship contribution statement

Gérard Xavier Gbenou: Writing – review & editing, Writing – original draft, Methodology, Formal analysis, Conceptualization. Boko Michel Orounladji: Writing – review & editing, Writing – original draft, Formal analysis, Data curation. Luc Hippolyte Dossa: Writing – review & editing, Writing – original draft, Supervision, Conceptualization. Denis Bastianelli: Writing – review & editing, Supervision, Formal analysis, Conceptualization. Ollo Sib: Writing – review & editing, Conceptualization. Bienvenu D'Ela Somda: Writing – review & editing, Investigation, Data curation. Palipougni Diabri: Writing – review & editing, Investigation. Florentin Sanou: Writing – review & editing, Investigation. Souleymane Sanogo: Writing – review & editing, Methodology. Laurent Bonnal: Writing – review & editing, Formal analysis. Paulo Salgado: Writing – review & editing, Conceptualization. Alexandre Ickowicz: Writing – review & editing, Conceptualization. Philippe Lecomte: Writing – review & editing, Writing – original draft, Data curation, Conceptualization. Mohamed Habibou Assouma: Writing – review & editing, Writing – original draft, Visualization, Supervision, Project administration, Formal analysis, Data curation,
Conceptualization.

## Ethics approval

This study was approved by the Ethics Committee of the Centre International de Recherche-Développement sur l'Elevage en zone Subhumide (CIRDES) under the Protocol No. 006/Mars/2021/CE-CIRDES, dated15 April 2021. All procedures involving animals were conducted in strict accordance with institutional guidelines for the care and use of animals in research.

The datasets generated and analyzed during the current study are not publicly available but are available from the corresponding author upon reasonable request.

## Declaration of generative AI and AI-assisted technologies in the writing process

During the preparation of this work the author(s) did not use any AI and AI-assisted technologies.

## Financial support statement

This study was made possible through the support of the “Carbon Sequestration and greenhouse gas emissions in (agro) Sylvopastoral Ecosystems in the sahelian CILSS States” (CaSSECS) regional project funded by the European Union (European DeSIRA programme, under grant agreement No FOOD/2019/410–169).

## Declaration of competing interest

The authors whose names are listed immediately below certify that they have no conflict, NO affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers' bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript. The manuscript represents valid work; neither this manuscript nor one with substantially similar content under our authorship has been published or is being considered for publication elsewhere (except as described in the manuscript submission); and copies of any closely related manuscripts are enclosed in the manuscript submission.

## Acknowledgements

The authors wish to thank Saïdou BOLI (CIRDES, 01 P.O. Box 454 Bobo-Dioulasso, Burkina Faso) for his support during data collection.

## Data availability

Data will be made available on request.

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