# Effects of partial substitution of corn ( Zea mays ) silage with napier grass ( Pennisetum purpureum ) silage on nutrient use and performance of dairy cows in the tropics

Elmer Edgardo Corea-Guillen, Gabriela Alejandra Flores, Sergio Daniel Molina, Manuel Vicente Mendoza, Aurora Hilda Ramirez-Perez, Augusto Cesar Lizarazo, Nelson Alirio Cruz Gutierrez, Joaquín Miguel Castro-Montoya, Mohammed Benaouda, Juan Carlos Angeles-Hernandez

► To cite this version:

Elmer Edgardo Corea-Guillen, Gabriela Alejandra Flores, Sergio Daniel Molina, Manuel Vicente Mendoza, Aurora Hilda Ramirez-Perez, et al.. Effects of partial substitution of corn ( Zea mays ) silage with napier grass ( Pennisetum purpureum ) silage on nutrient use and performance of dairy cows in the tropics. Italian Journal of Animal Science, 2025, 24 (1), pp.2334-2345. 10.1080/1828051X.2025.2578317. hal-05380828

HAL Id: hal-05380828

https://institut-agro-dijon.hal.science/hal-05380828v1

Submitted on 25 Nov 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>
# Effects of partial substitution of corn (*Zea mays*) silage with napier grass (*Pennisetum purpureum*) silage on nutrient use and performance of dairy cows in the tropics

Elmer Edgardo Corea-Guillen, Gabriela Alejandra Flores, Sergio Daniel

Molina, Manuel Vicente Mendoza, Aurora Hilda Ramirez-Perez, Augusto

Cesar Lizarazo, Nelson Alirio Cruz Gutierrez, Joaquín Miguel Castro-Montoya, Mohammed Benaouda & Juan Carlos Angeles-Hernandez

**To cite this article:** Elmer Edgardo Corea-Guillen, Gabriela Alejandra Flores, Sergio Daniel Molina, Manuel Vicente Mendoza, Aurora Hilda Ramirez-Perez, Augusto Cesar Lizarazo, Nelson Alirio Cruz Gutierrez, Joaquín Miguel Castro-Montoya, Mohammed Benaouda & Juan Carlos Angeles-Hernandez (2025) Effects of partial substitution of corn (*Zea mays*) silage with napier grass (*Pennisetum purpureum*) silage on nutrient use and performance of dairy cows in the tropics, Italian Journal of Animal Science, 24:1, 2334-2345, DOI: 10.1080/1828051X.2025.2578317

**To link to this article:** https://doi.org/10.1080/1828051X.2025.2578317

<figure><img src="image_2.png" /></figure>

© 2025 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.

<figure><img src="image_3.png" /></figure>

Published online: 06 Nov 2025.

<figure><img src="image_4.png" /></figure>

Submit your article to this journal

<figure><img src="image_5.png" /></figure>

Article views: 248

<figure><img src="image_6.png" /></figure>

View related articles

<figure><img src="image_7.png" /></figure>

CrossMark

View Crossmark data
<figure><img src="image_8.png" /></figure>

# Effects of partial substitution of corn (Zea mays) silage with napier grass (Pennisetum purpureum) silage on nutrient use and performance of dairy cows in the tropics

Elmer Edgardo Corea-Guillen<sup>a,b</sup>, Gabriela Alejandra Flores<sup>b</sup>, Sergio Daniel Molina<sup>b</sup>, Manuel Vicente Mendoza<sup>b</sup>, Aurora Hilda Ramirez-Perez<sup>c</sup>, Augusto Cesar Lizarazo<sup>d</sup>, Nelson Alirio Cruz Gutierrez<sup>e</sup>, Joaquín Miguel Castro-Montoya<sup>f</sup>, Mohammed Benaouda<sup>g</sup> and Juan Carlos Angeles-Hernandez<sup>h</sup>

<figure><img src="image_9.png" /></figure>

<sup>a</sup>Master's and Doctoral Program in Animal Husbandry and Health Sciences, National Autonomous University of Mexico, Mexico City, Mexico; <sup>b</sup>Department of Animal Husbandry, Faculty of Agricultural Sciences, University of El Salvador, San Salvador, El Salvador; <sup>c</sup>Department of Animal Nutrition and Biochemistry, Faculty of Veterinary Medicine and Zootechnics, National Autonomous University of Mexico, Mexico City, Mexico; <sup>d</sup>Centre for Practical Teaching and Research in Animal Production and Health (CEPIPSA), Faculty of Veterinary Medicine and Zootechnics, National Autonomous University of Mexico, Mexico City, Mexico; <sup>e</sup>Department of Matematic Sciences and Informatic, University les Illes Balears, Palma de Mallorca, Spain; <sup>f</sup>Institute of Agrifood and Environmental Sciences, Faculty of Agricultural Sciences, University of El Salvador, San Salvador, El Salvador; <sup>g</sup>Institut Agro Dijon, Dijon, France; <sup>h</sup>Department of Ruminant Medicine and Zootechnics, Faculty of Veterinary Medicine and Zootechnics, National Autonomous University of Mexico, Mexico City, Mexico

## ABSTRACT

This study evaluated the effect of partially replacing corn silage (CS) with napier grass silage (NS) in dairy cow diets on nutrient utilisation and performance. Eighteen lactating Holstein cows (BW 533 ± 58 kg; DIM 91 ± 41 d; MY 23.9 ± 3.4 kg/d) were allocated to two groups of nine in a crossover design. The CS diet contained 400 g/kg DM of CS, while the NS diet contained 300 g/kg DM of NS and 100 g/kg DM of CS. Both diets also included 80 g/kg of napier grass and 20 g/kg of Swazigrass. The experiment consisted of two 21-day periods, comprising 15 days of adaptation and six days of sampling. Feed, refusals, faeces and milk samples were taken for nutrient analysis and urine samples were taken for nitrogen and purine derivatives analysis. Intake and digestibility of DM, OM, CP, NDF and ADF, as well as milk yield and composition, nitrogen excretions and microbial protein synthesis (MPS), were estimated. Cows fed NS had greater daily DM intake (20.4 vs 19.5 kg), OM intake (18.2 vs 17.5 kg), CP intake (3566 vs 3420 g) (*p* < 0.05), greater DM digestibility, OM digestibility, NDF digestibility, ADF digestibility (*p* < 0.05), and MPS (1820 vs 1574 g/d, *p* < 0.05). Napier silage also increased lactose concentration and yield. Replacing partial CS with NS in the diet of dairy cows increased intake and digestibility of nutrients and MPS, with no detrimental effect on milk yield or composition.

## HIGHLIGHTS

* Napier grass silage can be produced with similar nutritional value to corn silage through appropriate management of the stage of maturity, wilting and adding corn meal.

* Including good-quality napier grass silage in the dairy diet increases intake and digestibility of nutrients and microbial protein synthesis.

* Feeding napier grass silage to dairy cows can permit similar milk yield and profit to that obtained with corn silage.

## ARTICLE HISTORY

Received 9 June 2025
Revised 14 October 2025
Accepted 15 October 2025

## KEYWORDS

Cattle; milk; silage; nitrogen

## Introduction

Dairy production in tropical regions is influenced by several constraints, including harsh climatic conditions and the low nutritional quality of locally available forages (Hernández-Castellano et al. 2019). Consequently, feeding high-producing dairy cows with such forages

is a significant challenge (Baris 2023). In most dairy systems worldwide, corn silage (Zea mays) is used as the primary forage, providing both fibre and energy to support elevated levels of milk production (Nichols et al. 1998; Bernardes and Rego 2014). The nutritional value of corn silage is influenced by its phenological

<figure><img src="image_10.png" /></figure>
<figure><img src="image_11.png" /></figure>

stage at harvest, the efficiency of the ensiling process,
and the use of additives to prevent undesirable fer-
mentation and heating (da Silva et al. 2015; Koakoski
et al. 2024). However, corn is a high-input crop, and
its productivity is highly susceptible to adverse envi-
ronmental conditions such as drought, elevated tem-
peratures (Li et al. 2022), prolonged vegetative growth
(Gentry et al. 2013), and pest infestations (Dhillon
et al. 2014). In view of the limitations previously men-
tioned, alternative forages such as sorghum (Sorghum
bicolor) (Khosravi et al. 2018) and napier grass
(Pennisetum purpureum) (Jobim et al. 2006) have
been the subject of investigation as substitutes for
corn silage. These alternatives have shown promising
results in supporting milk production under tropical
conditions (Ruiz et al. 1995; Jobim et al. 2006).

Napier grass is widely cultivated in tropical and
subtropical regions due to its high biomass yield,
favourable nutritional profile, and relatively simple
agronomic management (Monção et al. 2019a). Its
ability to produce large quantities of forage under
tropical conditions makes it a promising alternative to
corn silage, especially in regions where corn produc-
tion is limited by high input costs, seasonal variability,
or susceptibility to drought. However, achieving high-
quality silage is challenging because napier grass is
low in dry matter and starch, despite its high sugar
content (Wadi et al. 2004). Several strategies have
been proposed to enhance its ensiling characteristics,
including optimising harvest timing (Monção et al.
2019b), supplementing with non-fibrous carbohydrates
(Silva et al. 2007; Monteiro et al. 2011) and applying
pre-wilting techniques such as sun-drying (Ferrari and
Lavezzo 2001; Oliveira et al. 2012). Therefore, this
study aimed to evaluate the effects of replacing corn
silage with napier grass silage in dairy cow diets on
feed intake, nutrient digestibility, nitrogen balance,
microbial protein synthesis, milk yield, and
composition.

Materials and methods

All the experimental procedures were approved by
the Institutional Committee for the Care and Use of
Experimental Animals (SICUAE DC-2023/2-1) of the
National Autonomous University of Mexico.

Location

The current study was conducted in an agroecological
region of dry tropical forest (Holdridge 1967) in
Sonsonate, El Salvador (13°43' N and 89°40' W), on a

commercial dairy farm located at 381 masl, with an
annual rainfall between 1800 to 1950 mm and an aver-
age annual temperature of 28 °C (MARN, 2022).

Animals

Eighteen Holstein cows with (average ± standard error of the mean) live weight of 533 ± 58 kg, 90.8 ± 41 days in milk and 23.9 ± 3.4 kg milk yield with no history of previous pathologies were used. The cows were randomly distributed in two experimental groups of nine cows each, ensuring that the groups were homogeneous with regard to weight, milk production and days in milk. The experiment consisted of two periods of 21 days (15 days of adaptation and 6 days of sampling) each, that is, 42 days in total. The experimental design consisted of a cross-over arrangement, so the cows were switched between treatments at the end of the first period.

The cows were housed per experimental group in 2
adjacent pens, with zinc sheet roofs, concrete floor,
and free stalls with sand floor. The pens had a con-
crete linear feed bunk and water bowls where feed
and water were available *ad libitum*. Milking was per-
formed mechanically at 03:00 and 15:00 h and to miti-
gate heat stress, cows were sprayed with water every
5 min for 60 s and continuously ventilated from 08:00
to 17:00 h with fans of 70 cm diameter.

Silage production

Forages for silage were established under irrigation
during the dry season (December). A corn (Pioneer®
P4039) field (2.5 ha) was sown manually, with 75 cm
distance between rows and 10 plants per linear metre,
for a density of 133,333 plants/ha. Similarly, 2.5 ha of
napier grass were sown using stakes with 4 to 5
internodes, placing 2 stakes next to each other con-
tinuously at about 20 cm depth and covering them
with soil at 75 cm between rows. Crops received urea
and ammonium sulphate for a total of 212 and 179 kg
N/ha for corn and napier grass, respectively with grav-
ity irrigation once a week. At 85 d of age, corn was
harvested with the grain in a doughy-hard state
(Abendroth et al. 2011) with a forage harvester and
chopper (Pecos® 9004, Nogueira Máquinas Agrícolas,
São Paulo, Brazil), at 5 cm from the ground and chop-
ping it to 2 cm particle size. Napier grass was har-
vested at 60 d of age with a weeding machine (Oleo
Mac, 755 master, Reggio Emilia, Italy), the forage was
wilted in the sun for 3 days and then chopped like the
corn crop. Subsequently, 136 kg of corn meal were
<figure><img src="image_12.png" /><figcaption>**Table 1.** Ingredients and chemical composition of experimental diets for dairy cows.</figcaption></figure>

<table><thead><tr><th>Ingredients, g/kg Dry Matter</th><th>Corn silage diet (CS)</th><th>Napier silage diet (NS)</th></tr></thead><tbody><tr><td>Soybean meal</td><td>156</td><td>147</td></tr><tr><td>Wheat bran</td><td>114</td><td>104</td></tr><tr><td>Molasses</td><td>55.5</td><td>55.5</td></tr><tr><td>Corn meal</td><td>136</td><td>155</td></tr><tr><td>Mineral salt</td><td>5.35</td><td>5.35</td></tr><tr><td>Salt</td><td>1.78</td><td>1.78</td></tr><tr><td>By pass fat</td><td>13.4</td><td>13.4</td></tr><tr><td>Calcium carbonate</td><td>6.64</td><td>6.64</td></tr><tr><td>Sodium bicarbonate</td><td>8.92</td><td>8.92</td></tr><tr><td>Diamond (Yeast culture)</td><td>2</td><td>2.00</td></tr><tr><td>Magnesium oxide</td><td>0.89</td><td>0.89</td></tr><tr><td><strong>Total concentrate,</strong></td><td>500</td><td>500</td></tr><tr><td>Corn silage</td><td>400</td><td>100</td></tr><tr><td>Napier silage</td><td>—</td><td>300</td></tr><tr><td>Fresh napier grass</td><td>80</td><td>80.0</td></tr><tr><td>Swazi hay</td><td>20</td><td>20.0</td></tr><tr><td><strong>Total forage</strong></td><td>500</td><td>500</td></tr><tr><td><strong>Total diet</strong></td><td>1000</td><td>1000</td></tr><tr><td>Nutritional composition*</td><td></td><td></td></tr><tr><td>DM, g/kg FM</td><td>368</td><td>338</td></tr><tr><td>CP g/kg DM</td><td>175</td><td>175</td></tr><tr><td>Metabolizable Energy, MJ/kg DM**</td><td>10.2</td><td>10.0</td></tr><tr><td>NDF, g/kg DM</td><td>383</td><td>353</td></tr><tr><td>ADF g/kg DM</td><td>193</td><td>185</td></tr></tbody></table>

added to every wagon containing 5000 kg (865 kg DM), for an estimated of 160 g/kg of DM. At harvest, corn yielded 11.5 ton of DM/ha while napier grass yielded 11.9 ton of DM/ha of forage. Both the corn and the napier grass were taken to a pile silo where each 20 cm layer of forage was compacted with a tractor. Finally, they were covered and sealed with black plastic until used after 30 days of fermentation.

## Experimental diets

Two isocaloric and isoenergetic diets were formulated to meet the nutritional requirements of lactating dairy cows with an average body weight of 550 kg and a milk yield of 25 kg/day, in accordance with NRC (Nutrient Requirements of Dairy Cattle) (2001) recommendations, using the CPM Dairy software (version 3.0). The experimental treatments were as follows: a corn silage-based diet (CS), containing 400 g of corn silage (CS) per kg of dry matter (DM), and a napier grass silage-based diet (NS), containing 300 g of napier grass silage (NS) plus 100 g of corn silage per kg of DM. Both diets also included 80 g of napier grass and 20 g of Swazi grass (Digitaria swazilandensis) per kg of DM, to complete 500 g/kg of total forage or a forage-to-concentrate ratio of 50:50 in DM. Concentrate was comprised of ingredients typically used in the zone, soybean meal as main protein source, corn meal as main energy source, wheat bran, sugarcane molasses, mineral salt, sodium chloride, bypass fat, calcium

carbonate, sodium bicarbonate, yeast culture and magnesium oxide (Table 1).

Diets were prepared daily using a horizontal mixer (Enorossi Henomixer, Perugia, Italy) and offered as a total mixed ration (TMR) twice daily, at 07:00 and 14:00. Feed allocation was adjusted to allow for a target refusal rate of 5% on an as-fed basis.

## Sampling and data collection

Cows were weighed using a cattle scale (SIPEL BH60, SIPEL de Argentina, Rosario, Argentina) on two consecutive days at the beginning of the experiment and at the end of each experimental period. Feed offered and refused was recorded daily on a pen basis. Representative samples (400 g) of the offered diets (CS and NS), ensiled and fresh forages, and refusals were collected daily for each treatment and stored at -20°C for further analysis. From each cow, faecal and urine samples were collected every two hours (07:00-17:00) over six consecutive days. Faeces (200 g) were obtained directly from the rectum and stored in plastic bags. Urine samples (1 L) were collected by perineal stimulation using opaque containers. A 100 mL aliquot was acidified with 20% (v/v) sulphuric acid to reduce the pH to below 3 and filtered using Whatman No. 42 filter paper (Thomas Scientific, Swedesboro, USA). From the filtrate, a 10 mL sample was taken for nitrogen (N) analysis. An additional 10 mL of the filtrate was diluted (1:5) with distilled water, and three 10 mL aliquots were stored in screw-cap plastic containers

<footnote>*According to laboratory analysis.</footnote>

<footnote>**According to balancing in the CPM Dairy V3 program.</footnote>
for creatinine and purine derivative analysis. All faecal and urine samples were frozen at -20°C until analysis.

Individual milk yield was recorded during milking at 03:00 and 15:00 using Waikato milk metres (Waikato Milking Systems, Hamilton, New Zealand). Additionally, 50 mL of milk per cow was collected during each milking in sterile plastic bags and stored at 4°C. Milk samples from two sub-periods (3 days each) were pooled (six samples per pool) for subsequent analysis.

## Laboratory analysis and calculations

Feed and refuse samples were thawed for analysis. Faecal and urine samples of 6 days were mixed and pooled per cow. Feed and refuse samples (200 g) were dried in a ventilated oven (100-800, Memmert GmbH and Co. KG®, Schwabach, Germany) at 60 °C for 48 h, while faeces were dried for 72 h at 60 °C to determine dry matter (DM). Dried samples were ground in a Wiley® mill (Arthur H. Thomas Co., Philadelphia, PA) to pass a 1 mm sieve.

The N was analysed in feed, refusals, freshly thawed wet faeces and nondiluted urine, using digestion DK and distillation UDK 129 units (VELP Scientifica, Usmate, Italy) to estimate crude protein (CP, N x 6.25) using the Kjeldahl procedure (AOAC 2005; method 990.13). Neutral detergent fibre (NDF) and acid detergent fibre (ADF) both inclusive residual ash, were analysed in feed, refuses and faeces using thermostable amylase, following the methods of Van Soest et al. (1991), using an Ankom® 200 fibre analyser (ANKOM technology, NY, USA). Ash was quantified by incineration (Method 942.05; AOAC 2005) in a muffle furnace (model LT 24/12/P320, Nabertherm®, Bremen, Germany) at 600 °C for 2 h. Acid-insoluble ash (AIA) was quantified in faeces to calculate faecal output (Van Keulen and Young 1977).

The diluted and acidified urine samples were thawed, homogenised and used for kinetic determination of creatinine and uric acid (CREJ2 and UA2, Roche Diagnostics, Mannheim, Germany) using a photometer (COBAS C 501 module, Roche Diagnostics, Mannheim, Germany). Allantoin was quantified according to the method proposed by Chen and Gomes (1992) by spectrophotometry (Jenway 6305, Cole-Palmer, Stone Staffs, UK).

In milk samples, concentrations (g/kg milk) of total solids, protein, fat, lactose, and milk urea nitrogen (MUN, mg/dL) were quantified using the Foss MilkoScan® F1 (Foss Electric, Hillerød, Denmark).

Nutrient intakes (DM, OM, CP, NDF, and ADF) were calculated based on daily feed intake, estimated from feed offered and refused, following the procedure of Corea et al. (2017). Then feed and refusal were converted to DM (kg/d) using its DM concentration. Nutrient amount (OM, CP, NDF and ADF) offered and refused was estimated by multiplying the amount of DM by its nutrient concentration. Then the daily nutrient intake was calculated as follows:

$$ \text{Nutrient intake } g = \text{offered nutrient } g - \text{refused nutrient } g $$

Daily faecal output was calculated as the quotient of AIA intake divided by the AIA concentration in faeces (Patel et al. 2011), nutrient excretion was computed from the amount of faeces and its nutrient concentration. The apparent total tract apparent digestibilities (ATTD) of MS, MO, CP, NDF, and ADF were estimated by considering the nutrient ingested minus the nutrient excreted divided by the intake and expressed in g/100 g.

The urine excretion (L/d) was estimated assuming 29 mg/kg BW as the excretion constant (Valadares et al. 1999). Urinary purine derivative (PD) excretions (mmol/d) were obtained by multiplying urine volume (L/d) by allantoin and uric acid concentrations (mmol/L). Ruminal microbial protein synthesis (MPS, g/day) was computed from absorbed microbial purines (Chen and Gomes 1992), calculated as the sum of daily uric acid and allantoin excretions, corrected by the fractions of endogenous PD in urine (0.385 mmol/kg BW<sup>0.75</sup>) and microbial purine bases absorbed and recovered in urine (0.85; Chen and Orskov 2004).

The daily amount (kg/d) of nutrients secreted in milk was obtained by multiplying the nutrient concentration (g/kg) by the kg of milk produced per day.

Feed costs (USD) per kg of DM and daily ration consumed (USD) were calculated from the average prices of feed purchased during the trial. The income over feed cost (IOFC = income from milk sales - feed cost) was calculated using an average selling price of USD 0.722/kg of milk.

## Statistical analysis

Data were analysed using the R-Studio program (version 4.0.2; R Core Team; Vienna, Austria) using the CrossCarry package (Cruz Gutierrez et al. 2024). Significance was set at *p* < 0.05. Two statistical models were used to determine the effect of forage (CS, NS) on the response variables for a crossover design:

For variables measured once in every cow over the period:
<figure><img src="image_13.png" /><figcaption>**Table 2.** Chemical composition of the forages and corn meal used in the production of experimental silages.</figcaption></figure>

<table><caption>**Table 3.** Intake and digestibility of nutrients in dairy cows fed diets based on corn silage (CS, Zea mays) or napier silage (NS, Pennisetum purpureum).</caption><thead><tr><th>Nutrient, g/kg</th><th>Napier Grass</th><th>Swazi grass</th><th>Napier grass silage</th><th>Corn silage</th><th>Corn meal</th></tr></thead><tbody><tr><td>Dry matter</td><td>173 ± 16.4</td><td>293 ± 112</td><td>233 ± 34.7</td><td>265 ± 13.9</td><td>892 ± 5.8</td></tr><tr><td>Organic matter</td><td>860 ± 16.6</td><td>836 ± 7.3</td><td>879 ± 11.6</td><td>911 ± 8.3</td><td>987 ± 1.8</td></tr><tr><td>Crude protein</td><td>110 ± 25.1</td><td>108 ± 30.2</td><td>112 ± 4.8</td><td>106 ± 6.5</td><td>82 ± 3.4</td></tr><tr><td>Neutral detergent fibre</td><td>627 ± 38.2</td><td>624 ± 34.6</td><td>452 ± 81.6</td><td>565 ± 20.3</td><td>106 ± 13.5</td></tr><tr><td>Acid detergent fibre</td><td>370 ± 32.5</td><td>336 ± 23.7</td><td>264 ± 50.4</td><td>315 ± 9.0</td><td>25 ± 3.8</td></tr></tbody></table>

<table><thead><tr><th rowspan="2">Nutrient</th><th colspan="5">P value</th></tr><tr><th>CS</th><th>NS</th><th>SEM</th><th>Treatment</th><th>Carry over</th></tr></thead><tbody><tr><td>Intake</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Dry matter (DM), kg</td><td>19.5</td><td>20.4</td><td>0.18</td><td>&lt;0.01</td><td>0.38</td></tr><tr><td>Organic matter (OM), kg</td><td>17.5</td><td>18.2</td><td>0.16</td><td>&lt;0.01</td><td>0.61</td></tr><tr><td>Digestible OM, kg</td><td>12.1</td><td>13.2</td><td>0.19</td><td>&lt;0.01</td><td>0.25</td></tr><tr><td>Crude protein (CP, N x 6.25), g</td><td>3420</td><td>3566</td><td>32</td><td>&lt;0.01</td><td>0.37</td></tr><tr><td>Neutral detergent fibre (NDF), g</td><td>7362</td><td>7103</td><td>165</td><td>&lt;0.01</td><td>&lt;0.01</td></tr><tr><td>Acid detergent fibre (ADF), g</td><td>3715</td><td>3727</td><td>87.1</td><td>0.04</td><td>0.02</td></tr><tr><td>Digestibility (g/100g)</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>DM</td><td>66.1</td><td>68.6</td><td>0.65</td><td>&lt;0.01</td><td>0.19</td></tr><tr><td>OM</td><td>69.8</td><td>72.4</td><td>0.63</td><td>&lt;0.01</td><td>0.12</td></tr><tr><td>CP</td><td>71.3</td><td>70.4</td><td>1.25</td><td>0.19</td><td>0.04</td></tr><tr><td>NDF</td><td>49.1</td><td>51.5</td><td>1.51</td><td>&lt;0.01</td><td>0.01</td></tr><tr><td>ADF</td><td>47.3</td><td>50.5</td><td>1.93</td><td>&lt;0.01</td><td>&lt;0.01</td></tr></tbody></table>

SEM, Standard error of the mean.

$$Y_{ij} = \mu + P_i + Td_{ij} + Rd_{i-1, j} + \beta NP_j + e_{ijk}$$

where *ij* is the observation of cow *i* in the period *j*;

μ, the general average of all the experiments;

P, the effect of the period (i = 1, 2),

Tij is the effect of the treatment applied in period *i* to cow *j*, (j = 1, ..., n)

Rdi-1,j is the carryover effect of the treatment applied in the previous period over the period *i* in the cow *j*,

β is the slope of the parity effect NPj of the cow *j*,

eij is the error that is independent among cows, with constant variance and mean 0.

For variables measured more than once in the period:

$$Y_{ijkt} = \mu + P_i + Td_{ij} + Rd_{i-1, j} + \beta NP_j + B_k + e_{ijk}$$

where

Yijk is the observation of the dependent variable in cow *i* in period *j*.

μ is the general average of all the experiments,

Pj is the effect of the period (i = 1, 2),

Tij is the effect of the treatment applied in period *i* to cow *j* (j = 1, ..., n),

Rdi-1, j is the carryover effect of the treatment applied in the previous period over the period *i* in the cow *j*,

β is the slope of the parity effect NPj of the cow *j*.

Bk is the effect of measurement time *k* over the response.

<table><caption>**Table 4.** Milk composition and nutrient production in cows fed diets based on corn silage (CS, Zea mays) or napier silage (NS, Pennisetum purpureum).</caption><thead><tr><th rowspan="2">Item</th><th colspan="5">P value</th></tr><tr><th>CS</th><th>NS</th><th>SEM</th><th>Treatment</th><th>Carry over</th></tr></thead><tbody><tr><td>Milk yield, kg/día</td><td>23.4</td><td>24.0</td><td>0.39</td><td>0.12</td><td>0.96</td></tr><tr><td>Milk/DMI</td><td>1.21</td><td>1.18</td><td>0.02</td><td>0.25</td><td>0.76</td></tr><tr><td>Fat content, g/kg</td><td>39.1</td><td>37.9</td><td>0.69</td><td>0.09</td><td>0.83</td></tr><tr><td>Fat yield, kg/d</td><td>0.91</td><td>0.91</td><td>0.02</td><td>0.79</td><td>0.86</td></tr><tr><td>Milk protein, g/kg</td><td>31.2</td><td>31.3</td><td>0.29</td><td>0.91</td><td>0.17</td></tr><tr><td>Milk protein, kg/d</td><td>0.73</td><td>0.75</td><td>0.02</td><td>0.14</td><td>0.41</td></tr><tr><td>Milk lactose, g/kg</td><td>46.1</td><td>46.6</td><td>0.18</td><td>0.01</td><td>0.70</td></tr><tr><td>Milk lactose, kg/d</td><td>1.08</td><td>1.12</td><td>0.01</td><td>0.04</td><td>0.92</td></tr><tr><td>Milk total solids, g/kg</td><td>125</td><td>124</td><td>0.67</td><td>0.22</td><td>0.35</td></tr><tr><td>Milk total solids, kg/d</td><td>2.93</td><td>2.99</td><td>0.05</td><td>0.27</td><td>0.79</td></tr><tr><td>MUN, mg/dL</td><td>14.9</td><td>14.0</td><td>0.51</td><td>0.35</td><td>0.01</td></tr></tbody></table>

SEM, Standard error of the mean; MUN, Milk urea nitrogen.

eijt is the error that is independent among cows, with constant variance and mean 0.

## Results

The nutritional composition of the forages and corn meal used in the production of napier silage is presented in Table 2. Under the conditions of this study, napier silage (NS) contained 113 g/kg less NDF and 51 g/kg less ADF than corn silage (CS).

Results of nutrient intake and digestibility are summarised in Table 3. Partial replacement of CS with NS (75% substitution on a DM basis) resulted in a higher DM intake (DMI) (20.4 vs. 19.5 kg/day; *p* < 0.01). Intake of DM, OM, digestible OM (DOM), and CP was significantly higher in cows fed the NS diet (*p* < 0.01). Conversely, NDF intake was lower in this group (*p* < 0.05), likely due to the lower NDF content of the NS diet (Table 1).

Apparent total tract digestibility (ATTD) of DM (68.6 vs. 66.1 g/100 g), OM (72.4 vs. 69.8 g/100 g), NDF (51.5 vs. 49.1 g/100 g), and ADF (50.5 vs. 47.3 g/100 g) was greater in cows fed the NS diet (*p* < 0.01). However, no difference was observed in the ATTD of CP between treatments (Table 3).

Milk yield did not differ significantly between treatments (24.0 vs. 23.4 kg/day; *p* = 0.12). Similarly, no differences were observed in most milk nutrient contents and daily nutrient yields (Table 4), except for lactose concentration and yield, which were higher in cows fed the NS diet (*p* < 0.05).
<figure><img src="image_14.png" /><figcaption>**Table 5.** Nitrogen (N) balance, microbial protein synthesis and N efficiency in dairy cows fed diets based on corn silage (CS, Zea mays) or napier silage (NS, Pennisetum purpureum).</figcaption></figure>

<table><thead><tr><th rowspan="2">Item</th><th rowspan="2">CS</th><th rowspan="2">NS</th><th rowspan="2">SEM</th><th colspan="2">P value</th></tr><tr><th>Treatment</th><th>Carry over</th></tr></thead><tbody><tr><td colspan="6"><strong>N balance</strong></td></tr><tr><td>N Intake, g/d</td><td>548</td><td>570</td><td>4.94</td><td>&lt;0.01</td><td>0.96</td></tr><tr><td>Faecal N, g/d</td><td>167</td><td>168</td><td>4.21</td><td>0.93</td><td>0.81</td></tr><tr><td>Urinary N, g/d</td><td>269</td><td>272</td><td>14.1</td><td>0.91</td><td>0.03</td></tr><tr><td>Milk N, g/d</td><td>117</td><td>120</td><td>1.91</td><td>0.11</td><td>0.38</td></tr><tr><td>Faecal N, Faecal N g/100 g N Intake</td><td>30.2</td><td>29.3</td><td>0.78</td><td>0.24</td><td>0.60</td></tr><tr><td>Urinary N, Urinary N g/100 g N Intake</td><td>49.5</td><td>48.0</td><td>2.72</td><td>0.03</td><td>0.04</td></tr><tr><td>N Use Efficiency, Milk N g/100 g N intake</td><td>21.5</td><td>21.2</td><td>0.33</td><td>0.44</td><td>0.43</td></tr><tr><td colspan="6"><strong>Microbial Protein Synthesis and efficiency</strong></td></tr><tr><td>PD excretion, mmol/d</td><td>366</td><td>415</td><td>18.8</td><td>&lt;0.01</td><td>0.64</td></tr><tr><td>Microbial protein synthesis, g/d</td><td>1574</td><td>1820</td><td>93.3</td><td>0.01</td><td>0.64</td></tr><tr><td>Microbial N/ N intake, g/g</td><td>0.46</td><td>0.52</td><td>0.02</td><td>0.03</td><td>0.69</td></tr><tr><td>Microbial N/ DOMI, g/kg</td><td>20.7</td><td>22.4</td><td>1.14</td><td>0.15</td><td>0.45</td></tr></tbody></table>

SEM, Standard error of the mean; N, nitrogen; PD, purine derivatives; DOMI, digestible organic matter intake.

Nitrogen intake was greater in the NS group (+22 g/day; *p* < 0.01), while the ratio of urinary N to N intake was lower (48.0 vs. 49.5%; *p* < 0.05). However, total daily nitrogen output via faeces, urine, and milk, as well as nitrogen use efficiency for milk production, did not differ between treatments (Table 5).

Cows receiving the NS diet showed higher urinary purine derivative (PD) excretion (415 vs. 366 mmol/day), microbial protein synthesis (MPS; 1820 vs. 1574 g/day), and microbial nitrogen efficiency (microbial N/N intake; 0.52 vs. 0.46; *p* < 0.05).

Although the cost of the consumed NS diet was significantly higher than that of the CS diet (*p* < 0.05; Table 6), there were no differences in milk income or income over feed cost (IOFC) between treatments (*p* > 0.05).

## Discussion

This study evaluated the nutritional impact of partially replacing corn silage with napier grass silage in dairy cow rations, considering multiple variables related to nutrient utilisation and microbial protein synthesis, and applying a crossover experimental design to ensure a precise and robust assessment of animal performance.

## Forage composition

The nutritional composition of NS observed in this study contrasts with findings from previous research. For instance, Townsend et al. (2013) and Cabral et al. (2006) reported a decrease in CP and an increase in NDF when napier grass was incorporated into CS. These discrepancies may be attributed to differences in forage maturity at harvest. In both studies, napier grass was harvested at a later stage (approximately

120 days), which is associated with increased fibre content and reduced soluble carbohydrates. Similarly, Chacón-Hernández and Vargas-Rodríguez (2009) found that delaying harvest from 60 to 90 days increased cellulose content and reduced both hemicellulose content and *in vitro* DM digestibility.

In contrast, the napier grass used in the present study was harvested at 60 days and ensiled with added corn meal, which likely contributed to its more favourable chemical composition (Table 1). The addition of corn meal may have enhanced both the fermentability and nutritional value of the silage. Our NS showed a higher DM content (232.9 vs. 167.7 g/kg) and lower concentrations of NDF (452.2 vs. 627.5 g/kg) and ADF (263.6 vs. 369.6 g/kg) compared to fresh napier grass, indicating improved ensiling quality.

It is well established that CS generally provides superior nutritional value compared to NS. For example, Ferreira et al. (1995) reported better weight gains in dairy heifers fed CS than in those consuming NS or a mixture of the two. Similarly, Ruiz et al. (1992) observed a decline in milk yield when CS was replaced by NS, likely due to the lower starch content in NS. Corn silage typically contains around 510 g/kg of grain, with starch accounting for approximately 400 g/kg of DM (Thomas et al. 2001), making it a critical energy source in dairy diets.

To address the limitations of NS, various strategies have been proposed, such as incorporating corn meal or agro-industrial by-products during ensiling. These additives not only improve DM content but also enhance the silage's nutritional and fermentative profiles (Bilal 2009; Bernardes et al. 2018). Additionally, sun pre-wilting prior to ensiling likely contributed to improved silage quality in our study. Excessive moisture in silage is associated with undesirable butyric fermentation and protein degradation (Ferrari and
<figure><img src="image_15.png" /><figcaption>**Table 6.** Economic comparison of feeding with diets based on corn silage (CS, Zea mays) or napier silage (NS, pennisetum purpureum) in dairy cows.</figcaption></figure>

<table><thead><tr><th rowspan="2">Variable</th><th colspan="5">P value</th></tr><tr><th>CS</th><th>NS</th><th>SEM</th><th>Treatment</th><th>Carry over</th></tr></thead><tbody><tr><td>Feeding cost, US$/d</td><td>7.22</td><td>7.36</td><td>0.06</td><td>0.04</td><td>0.89</td></tr><tr><td>Milk income, US$/d*</td><td>16.9</td><td>17.3</td><td>0.28</td><td>0.12</td><td>0.96</td></tr><tr><td>Income over feed cost, US$/d</td><td>9.66</td><td>9.96</td><td>0.27</td><td>0.25</td><td>0.98</td></tr><tr><td>Feed cost/ milk income</td><td>0.48</td><td>0.49</td><td>0.03</td><td>0.91</td><td>0.29</td></tr></tbody></table>

Lavezzo 2001), both of which were likely mitigated by our pre-wilting procedure. Nevertheless, it is possible that silage characteristics can still be improved, e.g., we obtained 233 and 265 g DM/kg of NS and CS, which is low. Probably with better spreading of napier grass on the ground and an earlier retire of irrigation, the DM would have been higher.

## Nutrient intake and digestibility

Most studies report higher nutrient intake in dairy cows fed CS compared to those fed NS. For example, Ruiz et al. (1992) and Cabral et al. (2006) observed reductions in DM, OM, and CP intakes when CS was replaced by NS. In contrast, Jobim et al. (2006) found no significant differences in DMI between diets based on these two forages. In the present study, however, cows fed NS diets exhibited significantly higher intakes of DM, OM, digestible OM, and CP (*p* < 0.05). This increased intake may be partially explained by the lower NDF content of the NS diet (353 g/kg DM) compared to the CS diet (383 g/kg DM), as excessive dietary fibre can limit intake due to ruminal fill.

According to Mertens (1994), DMI is maximised when NDF intake reaches approximately 12.5 g/kg of BW, beyond which ruminal fill becomes a limiting factor. It has been considered that higher dietary NDF, regardless of the source of forage, reduced DM and OM intake but increase NDF and ADF absolute intakes as shown by Ruiz et al. (1995) and Nichols et al. (1998). Furthermore, the NDF digestibility has been shown to be positively related to DMI and consequently with milk yield (Oba and Allen 1999) or weight gain in beef cattle fed tropical diets (Detmann et al. 2024). Therefore, the lower NDF content and better digestibility (discussed below) in the NS diet likely contributed to the improved intake observed in our study.

Digestibility of forage nutrients—specifically DM, OM, NDF, and ADF—is influenced by the relative proportions of structural carbohydrates (i.e. hemicellulose

and cellulose) and lignin versus non-fibrous carbohydrates (NFC; mainly starches and sugars). Cabral et al. (2006, 2008) compared CS and NS and reported NDF contents of 521 and 566 g/kg DM for CS and 690 and 754 g/kg DM for NS, respectively. Meanwhile, NFC contents were 316 and 313 g/kg DM for CS, and significantly lower for NS at 141 and 119 g/kg DM, respectively. These differences resulted in higher ruminal, post-ruminal, and total tract digestibility for CS-based diets in those studies.

In contrast, the improved digestibility observed in the current study for cows on the NS diet—reflected by greater apparent total tract digestibility (ATTD) of DM, OM, NDF, and ADF (*p* < 0.01)—is likely due to several factors: (1) the early harvest stage of the napier grass (60 days), and (2) the inclusion of corn meal at 160 g/kg of fresh forage during ensiling, which contributed approximately 36 g/kg of starch to the DM. The added corn meal likely enhanced NFC content and fermentability, counterbalancing the inherently low starch levels in napier grass.

This interpretation is supported by Monteiro et al. (2011), who found that the addition of 490 g/kg DM of corn meal in fresh or ensiled napier grass significantly reduced NDF, ADF, and indigestible NDF, while increasing total digestible nutrients (TDN). Similarly, Ortiz et al. (2017) demonstrated that adding corn meal (50 to 200 g/kg DM) to maralfalfa (Pennisetum sp.) at 40 and 60 days of age increased DM content, decreased cellulose concentrations, and enhanced *in vitro* DM digestibility. In our case, the added starch from corn meal, combined with the naturally high sugar content of young napier grass, likely resulted in a higher NFC concentration in the NS diet. This, along with the enhanced NDF and ADF digestibility, helps explain the superior ATTD of DM and OM, as well as the higher nutrient intake in the NS treatment (Table 3).

Harvest age is a critical factor influencing the nutritional value of napier grass. Monção et al. (2019a) reported linear declines in CP and TDN and increases in NDF, ADF, and lignin with advancing maturity (30 to 120 days), thus, decreasing the effective ruminal degradability of DM and NDF during the dry season. Similarly, Monção et al. (2019b) found that increasing harvest age from 30 to 150 days in the rainy season caused similar changes in nutrient concentration and reduced *in vitro* digestibility of DM, CP, and NDF. Chacón-Hernández and Vargas-Rodríguez (2009) also reported a decrease in *in vitro* DM digestibility from 587 to 520 g/kg when napier grass was harvested at 90 rather than 60 days.

<footnote>*Estimated based on daily production and a price of $0.722 per litre of milk.</footnote>

<footnote>SEM, Standard error of the mean.</footnote>
Taken together, these findings suggest that the adverse effects reported in previous studies when replacing CS with NS—such as reduced intake, digestibility, and animal performance—are likely related to the more advanced maturity of the napier grass used. The positive outcomes observed in the current study highlight the importance of early harvest and appropriate silage supplementation strategies as adding corn meal, to enhance the feeding value of napier grass.

## Milk yield, milk composition, and nutrient yield

The milk yield obtained from NS diet is comparable to that of CS (24.0 vs 23.4 kg, Table 4), probably the slightly lower content of NDF (Table 1) and consequently higher energy, as well as greater nutrient intake and digestibility in the diet based on NS is related to this outcome. Ruiz et al. (1992) progressively replaced CS with NS (0 to 380 g/kg of dietary DM) using NS (190 g/kg of DM, 718 g/kg of NDF), this increased the NDF content in the diets and was associated with linear decreases in milk production (from 23.5 to 22.0 kg/day). Nonetheless, Jobim et al. (2006) found equivalent milk production in dairy cows fed NS with those fed CS diets. On the other hand, Ruiz et al. (1995) investigated the effect of three NDF concentrations (310, 350, and 390 g/kg) in the diet of lactating cows, using four forage sources that included CS and NS, showing that increasing NDF, milk production, protein and fat concentrations decreased linearly. However, when comparing CS versus NS diets with the same NDF contents, they found no differences in milk yield. It should be noted that Ruiz et al. (1992) compared CS with NS with different NDF contents; while Jobim et al. (2006) and Ruiz et al. (1995) compared them with similar NDF contents in isoenergetic and isonitrogenous diets, leading to similar milk production, as observed in the present study (Table 4). On the other hand, studies using CS and NS did not observe differences in nutrient content in milk from dairy cows (Ruiz et al. 1992; 1995; Jobim et al. 2006), zebu cows (Bilal 2008), or goats (da Silva et al. 2014), which was also observed in the present study, with the exception of lactose, which was higher in the milk of NS cows.

These results could be explained by a higher DM intake and therefore higher energy intake in NS cows as lactose concentration in milk increases with higher dietary energy intake (Zhou et al. 2015; Costa et al. 2019), cows fed with low energy density presented a negative energy balance and a 15/100 reduction in

the lactose concentration compared to the group fed with the correct energy density (Ouweltjets et al. 2007).

Although milk production in NS cows was not lower than CS cows, which is a positive finding that confirm our hypothesis, is still not clear why these cows did not have a better performance considering higher nutrient intake and digestibility, probably the NH3-N, starch content or VFA profiles in forages and diets that were not determined in the study, could contribute to a better understanding to this.

## Nitrogen balance and microbial protein synthesis

Some studies have compared N partitioning based on the intake of different silages that consider carbohydrate source and protein. Benchaar et al. (2014) studied nitrogen excretion in dairy cows fed varying proportions of corn:barley silage (0:54, 27:27, and 54:0 in DM), showing that increasing CS resulted in higher starch and lower NDF content in the diet and hence, a greater amount of N moved towards milk and less N excreted in urine. Similarly, Hassanat et al. (2013) replaced CS in dairy cow diets with alfalfa silage at DM ratios of 56:0, 28:28, and 0:56, observing improved N use efficiency in milk (NUE) and lower N excretion in urine, possibly because the CS diets had higher starch and lower NDF content. On the other hand, Colombini et al. (2012) used whole plant sorghum and sorghum silage; but with starch and NDF contents balanced by the inclusion of corn meal. Thus, they found no differences in the amount of N excreted by milk and urine.

The role of dietary CP concentration (and N intake) in the distribution and excretion of N has been reported by several authors, Olmos Colmenero and Broderick (2006) and Wattiaux and Karg (2004) reported that as the dietary concentration of CP increases from 135 to 194 g/kg DM or exceeds the NRC recommendation (2001), the efficiency of N utilisation for milk decreases, increasing faecal and urinary excretion. The lack of differences in most N partition parameters (Table 5) in the present study may be attributed to the fact that CP was similar in the NS and CS diets (175 g/kg) and the differences in NDF (353 vs 383 g/kg), and presumably starch, between the NS and CS diets (Table 1) were not as marked as in other studies. However, we observed higher N intake and a decrease in urinary N as a proportion of N intake (49.5 vs 48 g/100 g, Table 5) in cows fed NS compared to CS (*p* < 0.05), which might be related to a better ruminal use N as discussed next.
<figure><img src="image_16.png" /></figure>

The MPS and its efficiency in relation to digestible
nutrients, mainly OM, are indicators of the good use
of N from the diet (Hoover and Stokes 1991), Greater
MPS and microbial N use efficiency (Microbial N/N
Intake) were observed in the NS group (p < 0.05).
However, the microbial N/DOMI ratio was similar in
both groups of cows, results that could be related to
the diets, nutrient intake, and digestibility. Cows fed
NS consumed less NDF, but more DM, DOM, and CP;
therefore, conditions such as higher fermentable
carbohydrate intake and available N could allow for
better N utilisation by ruminal microbes in these cows.
The carbohydrate source affects microbial protein syn-
thesis (MPS), as demonstrated by Hristov et al. (2005),
who reported that cows receiving 206 g/kg of corn
starch, corn dextrose, or their mixture produced more
microbial N than cows receiving 206 g/kg of NDF in
the same basal diet concluding that a higher supply
of fermentable carbohydrates increases microbial
uptake of ammonia released in the rumen and hence,
the efficiency of microbial N use for milk production.
Similarly, Owens et al. (2009) reported higher microbial
N production in CS-based diets compared to grass sil-
age (perennial rye grass, Lolium perenne) in steers, CS
contained 307 g of starch/kg of DM, while grass silage
contained no starch.

Ruminal fermentation and the flow of microbial N to the intestine are affected by the quality and quantity of feed intake and by the energy and protein sources. Feeding carbohydrates and proteins that are not degradable in the rumen increases the amount of bypass protein, which decreases MPS (Clark et al. 1992). Zhu et al. (2013) fed cows isonitrogenous and isoenergetic diets containing alfalfa hay or CS. Both diets were balanced for 240 g/kg of starch; however, the alfalfa hay diet had a higher NFC content and a lower NDF content and lead to higher MPS, N conversion to milk, ruminal OM degradability, and lower MUN. We also found higher MPS when feeding isonitrogenous and isoenergetic diets with less intake of a more digestible NDF but more DOMI in the NS diet, which is consistent with the higher proportion of N excreted in urine in CS diet as excess ammonia not captured for MPS is absorbed and metabolised by the liver to urea, which is excreted in the urine (Brito et al. 2007)

Economic comparison

Although differences in feeding costs were observed
due to the higher DMI in the NS diet, milk income
and income over feed cost (IOFC) were similar for

both diets. In a similar study, Jobim et al. (2006) dem-
onstrated that NS-based diets generated milk produc-
tion equivalent to that of CS in dairy cows, with a
higher net profit margin per litre of milk obtained
with NS. These results support the feasibility of using
NS to replace CS in dairy cow feed without compro-
mising production and profit from milk sales.

Conclusions

The production of NS with a similar nutritional com-
position to CS is possible through management practi-
ces such as harvest age, pre-wilting and the use of a
non-structural carbohydrate source such as corn meal.
These conditions could increase DM, OM, DO, and CP
intakes, as well as improve DM, OM, NDF, and ADF
digestibility of NS diets compared to diets containing
CS in dairy cows. Contrary to this experience, studies
using NS at older ages reported lower nutritional
value and a negative impact on milk production.

Under our experimental conditions, diet partial
replacement of CS with NS produced with good man-
agement practices can permit similar milk and milk
nutrient production in dairy cows. It can also improve
nitrogen use efficiency, as demonstrated by higher
MPS. Furthermore, milk marketing revenues and profit
margins can be equivalent to those obtained with CS,
with the advantage that napier grass is less demand-
ing than corn in terms of agronomic management,
representing a valuable opportunity for dairy produc-
tion in the tropics.

Acknowledgements

The authors acknowledge the Scientific Research Council of the University of El Salvador for grant 15.37, National Council of Humanities, Sciences and Technologies (CONAHCYT) of México for grant 1189760. The authors are grateful to Velado S.A. de C.V. and its working staff, especially Jessica Santos, for the use of cows and their kind support for this research. The support of the Chemistry Department staff at the Faculty of Agriculture of the University of El Salvador on laboratory analysis of the samples is highly appreciated.

Disclosure statement

The authors report there are no competing interests to declare.

ORCID

Juan Carlos Angeles-Hernandez http://orcid.org/0000-0001-5303-1685
<figure><img src="image_17.png" /></figure>

# Data availability statement

Data will be made available on request.

# References

AOAC. 2005. Official Methods of Analysis of AOAC international. 18th Ed.

Abendroth LJ, Elmore RW, Boyer MJ, Marlay SK. 2011. Corn growth and development. https://store.extension.iastate.edu/product/6065

Baris A. 2023. Impact of feed quality on livestock productivity. JLP. 2(1):1–8. https://doi.org/10.47604/jlp.v2i1.2112

Benchaar C et al. 2014. Methane production, digestion, ruminal fermentation, nitrogen balance, and milk production of cows fed corn silage- or barley silage-based diets. J Dairy Sci. 97(2):961–974. https://doi.org/10.3168/jds.2013-7122

Bernardes TF et al. 2018. Silage review: unique challenges of silages made in hot and cold regions. J Dairy Sci. 101(5): 4001–4019. https://doi.org/10.3168/jds.2017-13703

Bernardes TF, Rego AC. 2014. Study on the practices of silage production and utilization on Brazilian dairy farms. J Dairy Sci. 97(3):1852–1861. https://doi.org/10.3168/jds.2013-7181

Bilal MQ. 2008. Feeding value of matt grass and its silage in lactating sahiwal cows. Pakistani J. Agri. Sci. 45(2):231–236. https://pakjas.com.pk/papers/189.pdf

Bilal MQ. 2009. Effect of molasses and corn as silage additives on the characteristics of mott dwarf elephant grass silage at different fermentation periods. Pakistan. Vet J. 29(1):19–23. http://pvj.com.pk/pdf-files/29_1/19-23.pdf

Brito AF, Broderick GA, Reynal SM. 2007. Effects of different protein supplements on omasal nutrient flow and microbial protein synthesis in lactating dairy cows. J Dairy Sci. 90(4):1828–1841. https://doi.org/10.3168/jds.2006-559

Cabral LS et al. 2006. Consumo e digestibilidade dos nutrintes em bovinos alimentados com dietas à base de volumosos tropicais [Intake and digestibility of nutrients in cattle fed diets based on tropical roughage]. R Bras Zootec. 35(6):2406–2412. Portuguese. https://doi.org/10.1590/S1516-35982006000800029

Chacón-Hernández PA, Vargas-Rodríguez CF. 2009. Digestibilidad y calidad del Pennisetum purpureum CV. King grass a tres edades de rebrote [Digestibility and quality of Pennisetum purpureum CV. King grass at three ages of regrowth]. Agron Mesoam. 20(2):399–408. Spanish. https://doi.org/10.15517/am.v20i2.4956

Chen XB, Gomes MJ. 1992. Estimation of microbial protein supply to sheep and cattle based on urinary excretion of purine derivatives- an overview of technical details. International Feed Resource Unit. Rowett Research Institute. [accessed 2023 Nov 27]. https://www.research-gate.net/publication/265323654_

Chen XB, Orskov ER. 2004. Research in urinary excretion of purine derivatives in ruminants: past, present and future. In Estimation of protein supply in ruminants using urinary purine derivatives (p. 180–210). Kuwer Academic Publishers. https://doi.org/10.1007/978-1-4020-2844-1_21

Clark JH, Klusmeyer TH, Cameron MR. 1992. Microbial protein synthesis and flow of nitrogen fractions to the duodenum

of dairy cows. J Dairy Sci. 75(8):2304–2323. https://doi.org/10.3168/jds.S0022-0302(92)77992-2

Colombini S, Galassi G, Crovetto GM, Rapetti L. 2012. Milk production, nitrogen balance and fiber digestibility prediction of corn whole plant, grain sorghum, and forage sorghum silages in the dairy cow. J Dairy Sci. 95(8):4457–4467. https://doi.org/10.3168/jds.2011-4444

Corea EE et al. 2017. Effects of dietary cowpea (*Vigna sinensis*) hay and protein level on milk yield, milk composition, N efficiency and profitability of dairy cows. Anim. Feed Sci. Technol. 226:48–55. https://doi.org/10.1016/j.ani-feedsci.2017.02.002

Costa A et al. 2019. Invited review: milk lactose Current status and future challenges in dairy cattle. J Dairy Sci. 102(7):5883–5898. https://doi.org/10.3168/jds.2018-15955

Cruz Gutierrez N, Melo O, Martínez C. 2024. A correlation structure for the analysis of Gaussian and non-Gaussian responses in crossover experimental designs with repeated measures. Stat Papers. 65(1):263–290. https://doi.org/10.1007/s00362-022-01391-z

da Silva JK et al. 2014. Elephant grass ensiled with wheat bran compared with corn silage in diets for lactating goats. R Bras Zootec. 43(11):618–626. https://doi.org/10.1590/S1516-35982014001100008

da Silva MSJ, Jobim CC, Poppi EC, Tres TT, Osmari MP. 2015. Production technology and quality of corn silage for feeding dairy cattle in Southern Brazil. R Bras Zootec. 44(9):303–313. https://doi.org/10.1590/S1806-92902015000900001

Detmann E, de Sousa LCO, Lima NSA, Franco MO. 2024. What is the impact of neutral detergent fibre digestibility on productive performance of beef cattle fed tropical forages? Livestock Sci. 290:105608. https://doi.org/10.1016/j.livsci.2024.105608

Dhillon MK, Kalia VK, Gujar GT. 2014. Insect-Pests and Their Management: current Status and Future Need of Research in Quality Maize. In: Chaudhary D, Kumar S, Langyan S. (eds) Maize: nutrition Dynamics and Novel Uses. Springer. https://doi.org/10.1007/978-81-322-1623-0_8

Ferrari E, Jr, Lavezzo W. 2001. Qualidade da silagem de capim-elefante (*Pennisetum purpureum*, Shum) emuchecido ou acrescido de farelo da mandioca [Quality of Elephantgrass Silage (*Pennisetum purpureum* Schum.) Wilted or Adding Cassava Meal]. Rev. Bras. Zootec. 30(5): 1424–1431. Portuguese https://doi.org/10.1590/S1516-35982001000600006

Ferreira JJ, Zuñiga MCP, Viana MCM. 1995. Silagem mista de capim-elefante e milho versus mistura de silagens de capim-elefante e de milho no desempenho de novilhas confinafas [Mixed elephant grass and corn silage versus mixture of elephant grass and corn silage on the performance of confined heifers]. R. Soc. Bras. Zootec. 24(6):1027–1037. Portuguese [accessed 2024 Oct 03]. https://www.sbz.org.br/revista/artigos/412.pdf

Gentry LF, Ruffo ML, Below FE. 2013. Identifying factors controlling the continuous corn yield penalty. Agron J. 105(2): 295–303. https://doi.org/10.2134/agronj2012.0246

Hassanat F et al. 2013. Replacing alfalfa silage with corn silage in dairy cow diets: effects on enteric methane production, ruminal fermentation, digestion, N balance, and milk production. J Dairy Sci. 96(7):4553–4567. https://doi.org/10.3168/jds.2012-6480
<figure><img src="image_18.png" /></figure>

Hernández-Castellano LE et al. 2019. Dairy science and health in the tropics: challenges and opportunities for the next decades. Trop Anim Health Prod. 51(5):1009–1017. https://doi.org/10.1007/s11250-019-01866-6

Holdridge LR. 1967. Life Zone Ecology. Tropical Science Center. San José, Costa Rica. p. 149.

Hoover WH, Stokes RS. 1991. Balancing carbohydrates and proteins for optimum rumen microbial yield. J Dairy Sci. 74(10):3630–3644. https://doi.org/10.3168/jds.S0022-0302(91)78553-6

Hristov AN et al. 2005. Effect of carbohydrate source on ammonia utilization in lactating dairy cows. J Anim Sci. 83(2):408–421. https://doi.org/10.2527/2005.832408x

Jobim CC, Sarti LL, dos Santos GT, Branco AF, Cecato U. 2006. Desempenho animal e viabilidade económica do uso da silagem de capim-elefante em substituição a silagem de milho para vacas em lactação [Animal performance and economic viability of using elephant grass silage to replace maize silage for lactating cows]. Acta Sci Anim Sci. 28(2):137–144. Portuguese. https://doi.org/10.4025/actascianimsci.v28i2.849

Khosravi M, Rouzbehan Y, Rezaei M, Rezaei J. 2018. Total replacement of corn silage with sorghum silage improves milk fatty acid profile and antioxidant capacity of Holstein dairy cows. J Dairy Sci. 101(12):10953–10961. https://doi.org/10.3168/jds.2017-14350

Koakoski DL, Bordin T, Cavallini D, Buonaiuto GA. 2024. Preliminary study of the effects of gaseous ozone on the microbiological and chemical characteristics of whole-plant corn silage. Fermentation. 10(8):398. https://doi.org/10.3390/fermentation10080398

Li E, Zhao J, Johannes Pullens JWP, Yang X. 2022. The compound effects of drought and high temperature stresses will be the main constraints on maize yield in Northeast China. Sci Total Environ. 812:152461. ISSN 0048-9697. https://doi.org/10.1016/j.scitotenv.2021.152461

Ministerio de Medio Ambiente y Recursos Naturales (MARN). 2022. Resumen climatológico anual 2021. [Annual climatological summary 2021]. El Salvador. Spanish. [accessed 2022 Sep 12]. https://www.snet.gob.sv/UserFiles/meteorologia/climatologico/ResumenClimatologicoAnual2021.pdf

Mertens DR. 1994. Regulation of forage intake, Chapter 11 In Forage quality, evaluation and utilization. Ed. Fahey Jr GC. American Society of Agronomy. p. 450–493. https://doi.org/10.2134/1994.foragequality.c11

Monção FP et al. 2019a. Productivity and nutritional value of BRS capiaçu grass (Pennisetum sp.) managed at four regrowth ages in a semiarid region. Trop Anim Health Prod. 52(1):235–241. https://doi.org/10.1007/s11250-019-02012-y

Monção FP et al. 2019b. Yield and nutritional value of BRS Capiaçu grass at different regrowth ages. SCA. 40(5):2045–2056. https://doi.org/10.5433/1679-0359.2019v40n5p2045

Monteiro IJG, de Abreu J, Cabral LS, Ribeiro MD, dos Reis RHP. 2011. Silagem de capim-elefante aditivada com produtos alternativos [Elephant grass silage supplemented with alternative products]. Acta Sci Animal Sci. 33(4):347–352. Portuguese. https://doi.org/10.4025/actascianimsci.v33i4.12629

Nichols SW, Froetschel MA, Amos HE, Ely LO. 1998. Effects of fiber from tropical corn and forage sorghum silages on intake, digestion, and performance of lactating dairy cows. J Dairy Sci. 81(9):2383–2393. https://doi.org/10.3168/jds.S0022-0302(98)70130-4

Nutrient Requirements of Dairy Cattle (NRC). 2001. 7th ed. National Academy Press.

Oba M, Allen MS. 1999. Evaluation of the importance of the digestibility of neutral detergent fiber from forage: effects on dry matter intake and milk yield of dairy cows. J Dairy Sci. 82(3):589–596. https://doi.org/10.3168/jds.S0022-0302(99)75271-9

Oliveira AC et al. 2012. Farelo de mandioca na ensilagem de capim-elefante: fracionamento de carboidratos e proteínas e características fermentativas [Cassava bran in elephant grass silage: carbohydrate and protein fractionation and fermentation characteristics]. Rev Bras Saúde Prod Anim. 13(4):1020–1031. Portuguese. https://doi.org/10.1590/S1519-99402012000400004

Olmos Colmenero JJ, Broderick GA. 2006. Effect of dietary crude protein concentration on milk production and nitrogen utilization in lactating dairy cows. J Dairy Sci. 89(5):1704–1712. https://doi.org/10.3168/jds.S0022-0302(06)72238-X

Ortiz F et al. 2017. Calidad fermentativa y nutricional de ensilados de maralfalfa (Pennisetum sp.) a diferentes edades de corte y niveles de maíz molido [Fermentative and nutritional quality of maralfalfa (Pennisetum sp.) silages at different cutting ages and maize grist levels]. Rev. FCA Uncuyo. 49(2):345–353. Spanish. https://revistas.uncu.edu.ar/ojs3/index.php/RFCA/article/view/3090/2240

Oueltjets W, Beerda B, Windig JJ, Calus MPL, Veerkamp RF. 2007. Effects of management and genetics on udder health and milk composition in dairy cows. J. Dairy Sci. 90(1):229–238. https://doi.org/10.3168/jds.S0022-0302(07)72624-3

Owens D, McGee M, Boland T, O’Kiely P. 2009. Rumen fermentation, microbial protein synthesis, and nutrient flow to the omasum in cattle offered corn silage, grass silage, or whole-crop weat. J Anim Sci. 87(2):658–668. https://doi.org/10.2527/jas.2007-0178

Patel M et al. 2011. Enteric methane emissions from dairy cows fed different proportions of highly digestible grass silage. Acta Agri Scandinavica, A - Animal Sci. 61(3):128–136. https://doi.org/10.1080/09064702.2011.616216

Ruiz TM, Bernal E, Staples CR, Sollenberger LE, Gallaher RN. 1995. Effect of dietary neutral detergent fiber concentration and forage source on performance of lactating cows. J Dairy Sci. 78(2):305–319. https://doi.org/10.3168/jds.S0022-0302(95)76639-5

Ruiz TM, Sanchez WK, Staples CR, Sollenberger LE. 1992. Comparison of ‘Mott’ dwarf elephantgrass silage and corn silage for lactating dairy cows. J. Dairy Sci. 75(2):533–543. https://doi.org/10.3168/jds.S0022-0302(92)77790-X

Silva FF et al. 2007. Bagaço de mandioca na ensilagem do capim-elefante: qualidade das silagens e digestibilidade dos nutrientes [Cassava bagasse in elephant grass silage: silage quality and nutrient digestibility]. Arq Bras Med Vet Zootec. 59(3):719–729. Portuguese. https://doi.org/10.1590/S0102-09352007000300026

Thomas ED et al. 2001. Comparison of corn silage hybrids for yield, nutrient composition, in vitro digestibility, and milk yield by dairy cows. J Dairy Sci. 84(10):2217–2226. https://doi.org/10.3168/jds.S0022-0302(01)74668-1

Townsend CR. et al. 2013. Composição químico-bromatológica da silagem de milho (Zea mays) com níveis
<figure><img src="image_19.png" /></figure>

de incluso de capim-elefante (Pennisetum purpureum) [Chemical-bromatological composition of maize (Zea mays) silage with levels of elephant grass (Pennisetum purpureum) inclusion.]. Circular Tecnica. 131 Embrapa[accessed 2024 Feb 13]. Portuguese. https://www.embrapa.br/busca-de-publicacoes/-/publicacao/1012043/composicao-quimico-bromatologica-da-silagem-de-milho-zea-mays-com-niveis-de-inclusao-de-capimelefante-pennisetum-purpureum

Valadares R, Broderick GA, Valadares Filho SC, Clayton MK. 1999. Effect of replacing alfalfa silage with high moisture corn on ruminal protein synthesis estimated from excretion of total purine derivatives. J Dairy Sci. 82(12):2686-2696. https://doi.org/10.3168/jds.S0022-0302(99)75525-6

Van Keulen J, Young BA. 1977. Evaluation of acid-insoluble ash as a natural marker in ruminant digestibility studies. J Anim Sci. 44(2):282-287. https://doi.org/10.2527/jas1977.442282x

Van Soest PJ, Robertson JB, Lewis BA. 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch

polysaccharides in relation to animal nutrition. J Dairy Sci. 74(10):3583-3597. https://doi.org/10.3168/jds.S0022-0302(91)78551-2

Wadi A, Ishii Y, Idota S. 2004. Effects of cutting interval and cutting height on dry matter yield and verwintering ability at the established year in Pennisetum species. Plant Prod Sci. 7(1):88-96. https://doi.org/10.1626/pps.7.88

Wattiaux MA, Karg KL. 2004. Protein level for alfalfa and corn silage-based diets: nitrogen balance and manure characteristics. J Dairy Sci. 87(10):3492-3502. https://doi.org/10.3168/jds.S0022-0302(04)73484-0

Zhou XQ et al. 2015. Effect of dietary energy source and level on nutrient digestibility, rumen microbial protein synthesis, and milk performance in lactating dairy cows. J Dairy Sci. 98(10):7209-7217. https://doi.org/10.3168/jds.2015-9312

Zhu W et al. 2013. Effects of dietary forage sources on rumen microbial protein synthesis and milk performance in early lactating dairy cows. J Dairy Sci. 96(3):1727-1734. https://doi.org/10.3168/jds.2012-5756