# Feed restriction and type of forage influence performance and behaviour of outdoor gestating sows

L. Aubé, F. Guay, R. Bergeron, G. Bélanger, G.F. Tremblay, S.A. Edwards, J.H. Guy, N. Devillers

► To cite this version:

L. Aubé, F. Guay, R. Bergeron, G. Bélanger, G.F. Tremblay, et al.. Feed restriction and type of forage influence performance and behaviour of outdoor gestating sows. Animal, 2021, 15 (10), pp.100346. 10.1016/j.animal.2021.100346. hal-04477839

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# Feed restriction and type of forage influence performance and behaviour of outdoor gestating sows

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

L. Aubé<sup>a,b,*</sup>, F. Guay<sup>b</sup>, R. Bergeron<sup>c</sup>, G. Bélanger<sup>d</sup>, G.F. Tremblay<sup>d</sup>, S.A. Edwards<sup>e</sup>, J.H. Guy<sup>e</sup>, N. Devillers<sup>a</sup>

## ARTICLE INFO

**Article history:**

Received 2 July 2020

Revised 23 July 2021

Accepted 30 July 2021

Available online 20 September 2021

**Keywords:**

Body condition

Grazing

Hay

Pasture

Sus scrofa

## ABSTRACT

Forages can contribute to the nutrient supply for sows but the extent to which they can replace concentrate feeding is not well known. The objective of this study was to assess the effect of level of feed restriction and type of forage on the performance and activity of gestating sows under outdoor conditions. A total of 45 sows were distributed among three treatments, with five replicates of three sows/treatment, from week 5 of gestation until farrowing. Treatments differed in the daily level of concentrate feed provided and the type of forage offered during gestation: 90% of metabolisable energy (ME) requirements provided by concentrates and free access to a pasture (P90); 40% of ME requirements provided by concentrates and free access to a pasture (P40); and 40% of ME requirements provided by concentrates and free access to a bare paddock with hay *ad libitum* (H40). From farrowing to weaning (5 weeks), concentrate feed was offered to all sows *ad libitum*. Body weight and backfat thickness (BF) were measured seven times during gestation and lactation. Postures of sows and time spent in the pasture were assessed at the beginning, middle and end of gestation. Forage intake was estimated with a method based on sow performance using the InraPorc® model. At farrowing, P90 sows were heavier and had greater BF than P40 and H40 sows. At weaning, P90 sows maintained a higher BW and tended to have greater BF than H40 sows, but no longer differed from P40 sows. Treatments did not influence litter size, but piglets from P40 sows were lighter at birth than those from P90 sows (1.44 vs. 1.69 kg, P = 0.004). In late gestation, P90 sows spent less time standing over 24 h and less time in the pasture during daytime than P40 sows, suggesting less foraging behaviour. Sows fed concentrates to meet 40% of ME requirements during gestation did not consume enough forage to maintain the same body condition as sows fed at 90% of ME requirements. Despite their inability to fully compensate for concentrate restriction during gestation by consuming more forage, P40 sows reached a similar body condition to P90 sows at weaning. In conclusion, forage intake for outdoor gestating sows can compensate a concentrate feed reduction of 10% and possibly more, but not as much as 60%.

Crown Copyright © 2021 Published by Elsevier B.V. on behalf of The Animal Consortium. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

## Implication

Results from previous studies suggest that forage could replace part of the concentrate feed given to gestating sows kept outdoors. In this study, sows fed concentrate at 40% of metabolisable energy requirements did not consume enough forage, either from pasture or hay, to compensate for this reduction during gestation. Nevertheless, sows fed at 40% of metabolisable energy requirements on

pasture reached a body condition at weaning similar to that of sows fed at 90%. These results suggest that under optimum conditions, pasture has good potential to replace part of the concentrate feed given to sows, but not as much as 60% of their metabolisable energy requirements.

## Introduction

Outdoor systems for swine may have multiple advantages that address societal concerns, since they promote animal welfare and environmental sustainability (Park et al., 2017). Additionally, forage-based systems have the potential to reduce feed costs as

<footnote><sup>a</sup>Sherbrooke Research and Development Centre, Agriculture and Agri-Food Canada, Sherbrooke, 2000 College Street, Sherbrooke J1M 1Z3, QC, Canada</footnote>

<footnote><sup>b</sup>Department of Animal Science, Université Laval, 2325, rue de l'Université, G1V 0A6 Quebec City, QC, Canada</footnote>

<footnote><sup>c</sup>Department of Animal Biosciences, University of Guelph, 50 Stone Road East ON, N1G 2W1 Guelph, ON, Canada</footnote>

<footnote><sup>d</sup>Quebec Research and Development Centre, Agriculture and Agri-Food Canada, 2560, Boulevard Hochelaga, G1V 2J3 Quebec City, QC, Canada</footnote>

<footnote><sup>e</sup>School of Natural and Environmental Sciences, Newcastle University, NE1 7RU Newcastle, United Kingdom</footnote>

<footnote>* Corresponding author at: VetAgro Sup - INRAE UMR 1213 Herbivores, 1 avenue Bourgelat, 69280 Marcy l'Etoile, France.
E-mail address: lydiane.aube@gmail.com (L. Aubé).</footnote>
forages can supply some of the energy and protein required by sows. The extent to which forages can replace concentrate feeding differs among studies. Muñoz Castillo et al. (2011) observed that feeding sows at 75% of the conventional concentrate feed level combined with *ad libitum* access to mulberry foliage did not affect body condition or reproductive performance (litter size and weight of piglets) and they estimated a decrease in total feed costs of 22.6% relative to conventional feeding. In a study by Honeyman and Roush (1999), sows that were fed concentrates at 40% of their requirements and had access to an alfalfa pasture achieved weight and backfat thickness gains similar to those of sows fed concentrate at 100% of their requirements in a drylot. In contrast, Eriksen et al. (2006) found that pregnant sows fed concentrate at 70% of their requirements with access to grass pasture and grass silage lost weight during pregnancy, suggesting that this concentrate feeding level was insufficient. Similarly, sows fed concentrate at 70% of their requirements with access to a star grass pasture mobilised their fat reserves during gestation and, thus, had lower BW and backfat thickness at farrowing than sows fed at 100% or 130% of their requirements, indicating that star grass did not supply sufficient compensatory energy to these sows (Santos Ricalde and Lean, 2002).

In practice, the extent to which pasture and roughage can contribute to the nutritional requirements of sows will depend on their voluntary forage intake and their ability to utilise the fibrous components. Sows' forage intake from pasture can be highly variable, given that many factors can influence grazing behaviour such as concentrate feeding level, ambient temperature, pasture characteristics and botanical composition, and season. Restricted concentrate feeding increased time spent grazing on star grass pastures of sows fed at 70% compared to sows fed at 100% of nutrient requirements (Santos Ricalde and Lean, 2002). Forage intake can be promoted by increasing the proportion of legumes because sows have shown preferences for legumes over grasses (Rachuonyo et al., 2005; Aubé et al., 2019). Therefore, knowledge of sows' voluntary forage intake as a function of the quality of the forage provided is essential to determine the level of concentrate feed that will maximise the performance of sows managed outdoors.

The objective of this study was to evaluate the potential for offering fresh or conserved forages to replace concentrate feed in the diet of gestating sows in an outdoor system under the humid continental climate of Eastern Canada. The effect of level of feed restriction and type of forage on the performance of sows and piglets as well as on sows' activity was investigated. Preliminary results have been published in an abstract (Aubé et al., 2018).

# Material and methods

## Animals and housing

The Institutional Animal Care Committee at the Sherbrooke Research and Development Centre (SRDC) of Agriculture and Agri-Food Canada (QC, Canada) approved the procedures (authorization # 523) in accordance with the guidelines of the Canadian Council on Animal Care (CCAC, 2009) and the Canadian Code of Practice for the Care and Handling of Pigs (NFACC, 2014). The experiment was conducted at the SRDC from April to November 2017.

For this study, 45 Yorkshire × Landrace sows, inseminated with Duroc semen, were distributed in five blocks. Sows in the same block were synchronised for oestrus: sows in the first block were artificially inseminated at the beginning of April, while sows in subsequent blocks were inseminated every two weeks thereafter. Sows were all second parity, except two sows, which were fourth parity; both 4th parity sows were allocated to the first block and

were allocated to two different treatments. Sows came from the SRDC indoor facility, where they had completed their previous parities. At insemination, sows weighed 214.1 ± 15.8 kg and had a backfat thickness (BF) of 18.7 ± 2.7 mm. At 4 weeks of gestation, sows were mixed in groups of three and, at week 5 of gestation, were dewormed and then moved to the outdoor system. The first block of sows was moved outdoors in mid-May and the last in mid-July.

The outdoor system always provided 24-h access to a permanent area of bare soil (10 × 25 m) for each group, with a shelter (3 × 3 m) containing straw bedding, a bowl drinker, a feeding pen (2.5 × 2.5 m) featuring individual troughs separated by partitions allowing individual feeding, and a wallow (Fig. 1). Straw bedding in the shelter was changed as needed and wallows were sprayed with water daily to maintain good mud consistency. Sows were individually fed concentrate, consisting mainly of corn, barley, and soybean meal (14.2 MJ of metabolisable energy (ME) /kg DM, 13.8% CP, Nutreco Canada, St-Hyacinthe, QC, Canada) in a single meal every morning around 8:30 a.m. The sows were not nose-ringed. At 16 weeks of gestation, the shelter was closed and three farrowing huts with straw bedding were installed in each plot. Sows were not induced to farrow. During farrowing, sows were monitored and oxytocin injection or manual assistance was used to extract the next piglet in the event of a prolonged interval between births.

## Experimental design and treatments

Within each of the five blocks, one group of three sows was allocated to each of three treatments, giving a total of 15 sows per treatment. Treatments differed in the daily level of concentrate feed provided and the type of forage offered during gestation: 90% of ME requirements provided by concentrates and free access to a pasture (P90); 40% of ME requirements provided by concentrates and free access to a pasture (P40); and 40% of ME requirements provided by concentrates and free access to a bare

<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Layout of outdoor experimental treatments showing permanent area, pasture plots (P90 and P40 sows), and the bare paddock (H40 sows only) provided to the sows. Treatments were as follows: P90, concentrate providing 90% of metabolisable energy (ME) requirements and access to a pasture plot; P40, concentrate providing 40% of ME requirements and access to a pasture plot; and H40, concentrate providing 40% of ME requirements and access to a bare paddock with hay provided *ad libitum* from a rack in the permanent area (not shown).</figcaption></figure>
paddock with hay ad libitum (H40). ME requirements were calculated using INRAPorc® software (Dourmad et al., 2008), which takes into account the level of physical activity, the predicted average ambient temperature, the expected litter size, and the expected change in weight and backfat thickness during pregnancy. The sows in the P90, P40, and H40 treatments received respectively 2.5 ± 0.09, 1.1 ± 0.01, and 1.1 ± 0.06 kg of concentrate feed, which corresponded to 31.3 ± 1.27, 14.1 ± 0.14, and 14.4 ± 0.75 MJ ME/day/sow. The 90% level was chosen as a treatment with a low energy supply from forage, whereas the 40% level was chosen as a treatment with a high energy supply from forage based on results from the study by Honeyman and Roush (1999). In order to allow for adaptation to outdoor housing and forage intake, the first measurements on sows and pastures started at week 7 of gestation.

From around day 100 of gestation, the amount of concentrate distributed daily to the sows was increased by 400 g for the P90 treatment and by 200 g for the P40 and H40 treatments. From week 16 of gestation, all sows were fed the same amount of feed but from a lactation diet composed mainly of corn, barley and soybean meal (14.8 MJ ME/kg, 19.7% CP, Nutreco Canada, St-Hyacinthe, QC, Canada). After farrowing, the amount of lactation concentrate feed given was gradually increased from 500 g on the day of farrowing to 5 kg on day 4 after farrowing. From day 5 after farrowing to weaning, sows were fed ad libitum.

Sows allocated to the P90 and P40 treatments had continuous access to a 2-year old pasture sown with a mix of red clover (Tri-folium pratense L., 7 kg/ha), timothy (Phleum pratense L., 7 kg/ha), birdsfoot trefoil (Lotus corniculatus L., 5 kg/ha), meadow bromegrass (Bromus biebersteinii Roem. & Schult., 5 kg/ha), and Kentucky bluegrass (Poa pratensis L., 3 kg/ha). Three 25 × 50 m pasture plots were used in rotation every 2 or 3 weeks for each group of three sows (Fig. 1). In order to standardise grass height and growth, pasture plots were mechanically clipped at an approximate height of 10 cm after each grazing period and left undisturbed to allow regrowth for 4 weeks before sows returned. Pasture plots used in

blocks 3, 4, and 5 were also clipped 4 weeks before the sows entered for the first time.

For the H40 treatment, sows had ad libitum access to hay provided in a covered rack in the permanent area. The hay consisted of a mix of red clover and timothy, harvested as the second cut in August 2016. These sows had access, without rotation, to a bare paddock (25 × 50 m) located in the same field as the other treatments. Paddocks were superficially tilled with a harrow before the sows entered in order to reduce the vegetation cover to a level as low as possible. Subsequently, the paddocks were tilled as needed to maintain a low vegetation cover to ensure that most of the forage intake came from the hay provided in racks.

## Climatic conditions

Temperatures from week 5 of gestation until farrowing were measured using the Environment Canada weather station located at the SRDC and are provided in Supplementary Table S1.

## Composition of forages and concentrates

Forages in the pasture and hay were sampled and analysed to determine their botanical and chemical composition using the methods presented in Supplementary Material S1. The chemical composition of concentrates was also determined. The biomass measured in pasture plots, the botanical composition of pasture and hay, the chemical composition of the fresh forage in pasture plots and the hay provided, along with the composition of the concentrate feed are given in Table 1.

## Data collection

### Sow performance

Body condition was assessed throughout the experiment. Body weight and backfat thickness were measured at breeding, at 7 (blocks 2, 4, and 5) or 8 (blocks 1 and 3) weeks of gestation, at

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

Botanical composition of pasture forage and hay, and chemical composition of pasture forage, hay, and concentrates offered to outdoor gestating sows.

<table><thead><tr><th rowspan="2"></th><th colspan="2">Pasture</th><th colspan="2">Hay</th><th colspan="2">Gestation concentrate</th></tr><tr><th>Mean</th><th>SD</th><th>Mean</th><th>SD</th><th>Mean</th><th>SD</th></tr></thead><tbody><tr><td colspan="7"><strong>Botanical composition (% DM)</strong></td></tr><tr><td>Red clover</td><td>39.2</td><td>11.7</td><td>74.4</td><td>14.6</td><td>-</td><td>-</td></tr><tr><td>Birdsfoot trefoil</td><td>6.2</td><td>3.2</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Timothy</td><td>16.6</td><td>9.1</td><td>19.9</td><td>15.9</td><td>-</td><td>-</td></tr><tr><td>Meadow bromegrass</td><td>3.1</td><td>2.6</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Kentucky bluegrass</td><td>3.0</td><td>2.0</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Other species*</td><td>31.8</td><td>14.6</td><td>5.7</td><td>5.1</td><td>-</td><td>-</td></tr><tr><td>Biomass available (g DM/m²)</td><td>279</td><td>103.8</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td colspan="7"><strong>Chemical composition</strong></td></tr><tr><td>DM (%)</td><td>17.4</td><td>2.6</td><td>87.7</td><td>1.9</td><td>88.7</td><td>0.2</td></tr><tr><td>CP (g/kg DM)</td><td>176</td><td>22.5</td><td>149</td><td>13.7</td><td>138</td><td>8.6</td></tr><tr><td>aNDF (g/kg DM)</td><td>453</td><td>29.9</td><td>487</td><td>25.3</td><td>133</td><td>13.9</td></tr><tr><td>ADF (g/kg DM)</td><td>334</td><td>23.0</td><td>325</td><td>15.3</td><td>54</td><td>8.0</td></tr><tr><td>NDICP (g/kg DM)</td><td>47.6</td><td>10.4</td><td>48.8</td><td>3.1</td><td>-</td><td>-</td></tr><tr><td>IVTD (g/kg DM)</td><td>832</td><td>30.4</td><td>842</td><td>14.9</td><td>-</td><td>-</td></tr><tr><td>NDFd (g/kg aNDF)</td><td>636</td><td>41.9</td><td>670</td><td>25.0</td><td>-</td><td>-</td></tr><tr><td>TC (g/kg DM)</td><td>704</td><td>31.3</td><td>765</td><td>16.9</td><td>-</td><td>-</td></tr><tr><td>NSC (g/kg DM)</td><td>293</td><td>26.3</td><td>330</td><td>19.6</td><td>-</td><td>-</td></tr><tr><td>P (g/kg DM)</td><td>3.8</td><td>0.5</td><td>2.8</td><td>0.2</td><td>6.3</td><td>0.5</td></tr><tr><td>Ca (g/kg DM)</td><td>11.2</td><td>1.3</td><td>8.0</td><td>0.8</td><td>11.0</td><td>1.1</td></tr><tr><td>ME (MJ/kg DM)</td><td>10.8</td><td>0.5</td><td>10.6</td><td>0.3</td><td>14.2</td><td>0.3</td></tr></tbody></table>

Chemical composition: aNDF = NDF assayed with a heat-stable α-amylase; NDICP = neutral detergent insoluble crude protein; IVTD = in vitro true digestibility of DM; NDFd = in vitro NDF digestibility; TCs = total carbohydrates; NSCs = non-structural carbohydrates; ME = metabolisable energy for sows.

ME was estimated according to the following equations:

The first equation estimates ME for growing pigs (MEg) (Noblet and Perez, 1993) as follows: $MEg = 4194 - (9.2 \times Ash) + (1.0 \times CP) + (4.1 \times EE) - (3.5 \times NDF)$.

Where EE = ether extract.

The second equation estimates ME for sows (MEs) based on MEg (Noblet and Shi, 1993) as: $MEs = 4.63 + (0.64 \times MEg) + (0.0096 \times EE) + (0.0029 \times CP)$.

<footnote>* Other species included mainly Microseris lanceolate, Capsella bursa-pastoris, Carex sp., and Elymus repens.</footnote>
11 (blocks 2, 4, and 5) or 12 (blocks 1 and 3) weeks of gestation, at 14 weeks of gestation for all blocks, and at 16 weeks of gestation for all blocks on day 1 (L1) and week 3 of lactation and, finally, at weaning in week 5 of lactation. Backfat measurements were performed by ultrasonography (WED-3000, Shenzhen WELL D Medical Electronics Co., Ltd., Shenzhen, China) at the P2 position, which is the level of the last rib and 65 mm off the midline. Gain in BW and backfat thickness along with gain in fat mass and protein mass were calculated for gestation, from breeding to L1, from L1 to weaning, and for the combined periods from breeding to weaning. Estimated fat mass and estimated protein mass were calculated according to the method of Dourmad et al. (1997), using empty BW and BF at insemination, L1, and weaning, as follows:

$$ \text{Lipid (kg)} = -26.4 + 0.221 \text{ Empty BW} + 1.331 \text{ BF} $$

$$ \text{Protein (kg)} = 2.28 + 0.178 \text{ Empty BW} - 0.333 \text{ BF} $$

$$ \text{with Empty BW} = \text{BW} \times 0.96 $$

The health status of the sows was closely monitored during the experiment. Reproductive performance was characterised by measuring the total number of piglets born (TPB), including stillborn ones, the length of each piglet from the crown of its head to the base of its tail, and the birth weight of piglets for each litter within approximately 20-43 h of birth (L1). Piglets were weighed again when they were weaned at 5 weeks of age and the average daily gain of each piglet was calculated. The percentage of TPB weighing less than 1 kg or more than 2 kg was calculated. In order to analyse the within-litter birth weight variation, the coefficient of variation of TPB birth weight was calculated. The body mass index (BMI) of each piglet was also calculated as follows (Hales et al., 2013):

$$ \text{BMI} = \frac{\text{birth weight}}{(\text{crown} - \text{rump length})^2} $$

### Sow behaviour

To assess sow activity, time spent standing and time spent at pasture were investigated. Sow activity was measured simultaneously, using a tracking GPS receiver to record location, and an accelerometer to record posture. Activity was measured three times during gestation, at weeks 9, 13, and 15 (blocks 1 and 3) or weeks 8, 12, and 15 (blocks 2, 4, and 5). The GPS receivers (GPS Sport LogBook, model GT-740FL, CanMore Electronics Corporation, Taiwan) were fixed between the shoulders of the sow and set to record location every 15 seconds, with a circular error probability accuracy of 2.5 m, for at least two 20 h periods per week of measurement. Location was recorded for treatments P90 and P40 only. The GPS data were processed using QGIS software (version 3.4) to remove any recording located outside a limit 2.5 m beyond the actual fence. On average, 4.5% of readings were removed. The location of the sow for each recording was considered to be inside the pasture plot or in the permanent area (Fig. 1).

The accelerometer (Pendant G Acceleration Data Logger, model UA-004-64, Onset Computer Corporation, Pocasset, MA, USA) was fixed on one lower back leg with the x-axis parallel to the leg using the method described by Ringgenberg et al. (2010). The accelerometer recorded acceleration on the x-axis every 5 seconds for all treatments, for two to three 24-h periods per week of measurement for each sow. Time spent standing was assessed according to the method of Ringgenberg et al. (2010) using a threshold of 0.59 g on the x-axis.

Location and posture data, which were recorded simultaneously, were merged in order to analyse each combination of posture (standing or not) and location (pasture or permanent area). Recordings were undertaken until a minimum of two periods of

at least 20 h for each sow per week were obtained, with a maximum of three periods for each sow per week. The mean recording duration of a period was 23.6 ± 0.4 h (mean ± SD), starting at 08:40 a.m. (±14 min), with the end of the recording at 08:16 a.m. (±30 min) the following day. Since most of the time sows spent in pasture (99.5 ± 2.7%; mean ± SD) and in a standing posture (98.8 ± 2.8%) occurred during daytime, activity in pastures was calculated as the percentage of time spent standing in the pasture over the daytime period (between sunrise and sunset).

### Hay intake estimation

For sows receiving hay (H40), the amount of hay distributed in the racks was noted and hay intake was evaluated by weighing hay refusal every two weeks over five × 2-week periods throughout gestation.

### Forage intake estimated via sows' performance

Forage intake of the sows during gestation for the P90, P40, and H40 treatments was also estimated based on theoretical ME requirements calculated by the INRAPorc model (Dourmad et al., 2008). INRAPorc has been used as a model to estimate forage intake as it takes into account the time spent standing by the sows that has been measured with accelerometers and the ambient temperature for a more precise estimation of the nutrient needs of the sows during gestation.

This estimation was based on the hypothesis that the theoretical ME requirements not fulfilled by concentrate feed would be met by forage intake. It was also calculated considering that energy was the main factor contributing to sows' performance and that other nutrients were not limiting for the growth and maintenance of the sow and foetal development.

As a first step, total ME requirements during gestation from breeding to farrowing were estimated on the basis of the litter size, the average ambient temperature and the daily activity, assessed as the time spent standing as measured with accelerometers, as well as changes in sows' BW and backfat thickness. As a second step, ME intake from concentrates was estimated by multiplying total concentrate intake by its ME concentration. The total amount of ME intake from the forages from week 5 of gestation to farrowing was then estimated by subtracting the amount of concentrate-derived ME from the estimated total ME requirement. Finally, the total amount of forage consumed was estimated by dividing the total amount of forage-derived ME by the average ME concentration of the forage (hay or pasture forage) and expressing the result on a per-day basis.

### Forage intake estimated using aerial images

To estimate the sows' forage intake from pasture, biomass disappearance was determined using a previously described method based on aerial imagery (Théau et al. 2021) through estimation of the amount of biomass at the beginning and at the end of grazing periods considering pasture growth during the period. This approach was examined but found to overestimate forage intake, because the disappearance of vegetation was not necessarily linked to ingestion, probably because unlike ruminants, pigs root and overturn the ground surface.

### Statistical analysis

Statistical analyses were performed using SAS® software (Statistical Analysis System, Release 9.4, 2002–2012, SAS Institute Inc., Cary, NC). Two sows aborted during the experiment, one in the P40 treatment in block 2 and one in the H40 treatment in block 4. Data for these two sows were totally removed. Data from two sows, one that lost all her piglets in the first days of lactation in the H40 treatment in block 2, and one that was euthanised for
health problems before weaning in the H40 treatment in block 5, were removed for the analysis of the lactation period.

Sow posture and location (time spent standing during 24-h periods and time spent standing in pasture during daytime) were analysed using a generalised complete block design with treatment as a fixed factor, week of gestation as repeated measures using the MIXED procedure of SAS, and the group of three sows as the experimental unit. Since the treatment × week of gestation interaction was significant, analyses of variance (with homogenous variances) were performed for each week of gestation separately, with treatment as a fixed factor and block as a random factor. The interaction of block × treatment was used as the error term for testing the effect of treatment.

Sow BW and backfat thickness were analysed using a generalised complete block design with treatment as a fixed factor, week of gestation as repeated measures using the MIXED procedure of SAS, and the sow as the experimental unit. Since the treatment × week of gestation interaction was significant, analyses of variance (with homogenous variances) were performed for each week of gestation separately, with treatment as a fixed factor and block as a random factor.

Gains in BW, BF, and fat and protein mass during gestation were analysed according to a generalised complete block design using the MIXED procedure of SAS. Analyses of variance were performed with treatment as a fixed factor, the block × treatment interaction and block as random factors, and the group of three sows as the experimental unit.

Gains in BW, BF, and fat and protein mass during lactation and over the entire period from insemination to weaning, piglet characteristics (number of TPB, weight and BMI of TPB at L1, CV of birth weight, percentages of TPB weighing more than 2 kg and less than 1 kg, weight at weaning, number of piglets weaned and average daily gain), and forage intake estimates were analysed according to a generalised complete block design using the MIXED procedure of SAS. Analyses of variance were performed with treatment as a fixed factor, block as a random factor, and the sow as the experimental unit. Angular transformation was applied to percentages of piglets weighing less than 1 kg and more than 2 kg. Given that a linear relationship existed between TPB and the other variables related to piglets, this variable was used as a co-variate for the analyses of weight, BMI, CV of birth weight at L1, percentage of piglets weighing less than 1 kg, and percentage of piglets weighing more than 2 kg.

To determine the evolution of hay intake for treatment H40, an analysis of variance with repeated measures (with week of gestation as repetition and block as subject) was performed using polynomial contrasts in the MIXED procedure of SAS with week of gestation as a fixed factor.

Posthoc comparisons between treatments (using Tukey's adjustments for more than two treatments) were undertaken when the treatment effect was significant. A probability level of P < 0.05 was chosen as the limit for statistical significance in all tests, whereas probability levels of 0.05 ≤ P < 0.10 were considered to be a trend. Data provided in tables, figures, and text are least square-means with SEM unless stated otherwise.

## Results

### Sow body condition

Sow BW at 7–8 weeks of gestation did not differ among treatments. From weeks 11–12 of gestation until the end of gestation, P90 sows were heavier than P40 (P < 0.001 at week 16) and H40 (P < 0.001 at week 16) sows (Fig. 2). During lactation, P90 sows maintained a greater BW than H40 sows (P = 0.004 at weaning).

<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Evolution of the sow BW during gestation (n = 43) and lactation (n = 41) (Least square-means ± SEM). <sup>a,b</sup>Different small letters indicate significant differences with *P* < 0.05; <sup>A,B</sup>Different capital letters indicate a tendency with 0.05 ≤ *P* < 0.10, (n = 43). P90: concentrate providing 90% of metabolisable energy (ME) requirements and access to a pasture plot; P40: concentrate providing 40% of ME requirements and access to a pasture plot; and H40: concentrate providing 40% of ME requirements and access to a bare paddock and hay *ad libitum*.</figcaption></figure>

The P90 sows had a greater BW than P40 sows only at L1 (P < 0.001) and tended to be heavier at week 3 of lactation (P = 0.08). At weaning, P40 sows tended to be heavier than H40 sows (P = 0.08) and they were no longer significantly different from P90 sows (P = 0.42).

Backfat thickness did not differ among treatments until the end of gestation. At week 16 of gestation, P90 sows had greater BF than P40 and H40 sows (P = 0.021 and P = 0.002, respectively; Fig. 3). During lactation, P90 sows had greater BF than H40 sows at L1 and at week 3 of lactation (P < 0.001 and P = 0.022, respectively); this difference tended to be significant at weaning (P = 0.09). P90 sows had greater BF than P40 sows only at L1 (P = 0.012); at weaning, no significant difference was observed between these treatments (P = 0.913). The BF of P40 and H40 sows did not differ significantly at any time during gestation or lactation.

Gains of BW, BF, protein mass and fat mass differed among treatments during the gestation and lactation periods and over the complete breeding to weaning interval (Table 2). During gestation, gains of BW, fat mass, and protein mass were greater for P90 sows than for P40 and H40 sows. Moreover, during gestation, P40 and H40 sows had a decrease in BF whereas P90 sows had an

<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Evolution of the backfat thickness of sows during gestation (n = 43) and lactation (n = 41) (Least square-means ± SEM). <sup>a,b</sup>Different small letters indicate significant differences with *P* < 0.05; <sup>A,B</sup>Different capital letters indicate a tendency with 0.05 ≤ *P* < 0.10, (n = 43). P90: concentrate providing 90% of metabolisable energy (ME) requirements and access to a pasture plot; P40: concentrate providing 40% of ME requirements and access to a pasture plot; and H40: concentrate providing 40% of ME requirements and access to a bare paddock and hay *ad libitum*.</figcaption></figure>
<caption>**Table 2**</caption>

Gain in BW and backfat thickness along with gain in estimated protein mass and lipid mass during gestation and lactation, and from breeding to weaning (Least square-means ± SEM) of outdoor gestating sows given 90% of metabolisable energy (ME) requirements from concentrate with access to a pasture plot (P90), 40% of ME requirements from concentrate with access to a pasture plot (P40), and 40% of ME requirements from concentrate with access to a bare paddock and hay ad libitum (H40).

<table><thead><tr><th rowspan="2"></th><th colspan="3">Treatment</th><th rowspan="2">P-value</th></tr><tr><th>P90</th><th>P40</th><th>H40</th></tr></thead><tbody><tr><td>Number of replicates<sup>†</sup></td><td></td><td></td><td></td><td></td></tr><tr><td>Gestation (breeding-L1)</td><td>5</td><td>5</td><td>5</td><td></td></tr><tr><td>Lactation (L1-weaning)</td><td>15</td><td>14</td><td>12</td><td></td></tr><tr><td>BW gain (kg/sow)</td><td></td><td></td><td></td><td></td></tr><tr><td>Gestation (breeding-L1)</td><td>52.4<sup>a</sup> ± 4.2</td><td>22.1<sup>b</sup> ± 4.2</td><td>9.6<sup>b</sup> ± 4.2</td><td>&lt;0.001</td></tr><tr><td>Lactation (L1-weaning)</td><td>-16.2<sup>a</sup> ± 6.1</td><td>6.9<sup>b</sup> ± 4.7</td><td>1.1<sup>b</sup> ± 5.9</td><td>&lt;0.001</td></tr><tr><td>Breeding-weaning</td><td>36.2<sup>a</sup> ± 4.6</td><td>29.2<sup>a</sup> ± 4.6</td><td>11.5<sup>b</sup> ± 4.6</td><td>0.001</td></tr><tr><td>Backfat thickness gain (mm/sow)</td><td></td><td></td><td></td><td></td></tr><tr><td>Gestation (breeding-L1)</td><td>1.4<sup>a</sup> ± 0.8</td><td>-3.0<sup>b</sup> ± 0.8</td><td>-4.6<sup>b</sup> ± 0.8</td><td>&lt;0.001</td></tr><tr><td>Lactation (L1-weaning)</td><td>-5.1<sup>a</sup> ± 0.9</td><td>-2.3<sup>b</sup> ± 0.9</td><td>-3.7<sup>ab</sup> ± 0.9</td><td>0.036</td></tr><tr><td>Breeding-weaning</td><td>-3.6<sup>a</sup> ± 1.3</td><td>-5.2<sup>a</sup> ± 1.1</td><td>-8.4<sup>b</sup> ± 1.0</td><td>&lt;0.001</td></tr><tr><td>Estimated fat mass gain (kg/sow)</td><td></td><td></td><td></td><td></td></tr><tr><td>Gestation (breeding-L1)</td><td>13.0<sup>a</sup> ± 1.3</td><td>0.8<sup>bA</sup> ± 1.5</td><td>-4.0<sup>bb</sup> ± 1.0</td><td>&lt;0.001</td></tr><tr><td>Lactation (L1-weaning)</td><td>-10.2<sup>aA</sup> ± 2.5</td><td>-1.5<sup>b</sup> ± 1.8</td><td>-4.7<sup>AB</sup> ± 2.1</td><td>0.002</td></tr><tr><td>Breeding-weaning</td><td>2.8<sup>a</sup> ± 2.5</td><td>-0.7<sup>a</sup> ± 2.5</td><td>-8.8<sup>b</sup> ± 2.5</td><td>&lt;0.001</td></tr><tr><td>Estimated protein mass gain (kg/sow)</td><td></td><td></td><td></td><td></td></tr><tr><td>Gestation (breeding-L1)</td><td>9.4<sup>a</sup> ± 0.8</td><td>2.8<sup>bA</sup> ± 0.8</td><td>0.1<sup>bb</sup> ± 0.8</td><td>&lt;0.001</td></tr><tr><td>Lactation (L1-weaning)</td><td>-4.4<sup>a</sup> ± 1.3</td><td>0.4<sup>b</sup> ± 1.0</td><td>-1.1<sup>b</sup> ± 1.2</td><td>&lt;0.001</td></tr><tr><td>Breeding-weaning</td><td>5.0<sup>a</sup> ± 1.1</td><td>3.3<sup>a</sup> ± 1.1</td><td>-0.9<sup>b</sup> ± 1.1</td><td>&lt;0.001</td></tr></tbody></table>

L1 = day 1 of lactation.

Fat mass and protein mass were estimated according to the following equations (Dourmad et al., 1997):

Lipid (kg) = -26.4 + 0.221 Empty BW + 1.331 Backfat thickness.

Protein (kg) = 2.28 + 0.178 Empty BW - 0.333 Backfat thickness.

with Empty BW = BW × 0.96.

† The statistical unit was a group of three sows in gestation and an individual sow in lactation and for breeding to weaning period.

a,b Within a row, values with different superscript small letters differ significantly at *P* < 0.05.

A,B Within a non-significantly different pair, values with different superscript capital letters tended (0.05 ≤ *P* < 0.1) to be different.

increase in BF. During gestation, none of the P90 and P40 sows lost weight, whereas one H40 sow lost weight and 20%, 93% and 100% of P90, P40 and H40 sows lost BF, respectively. During the lactation period, gains of BW, fat mass and protein mass were greater for P40 and H40 sows than for P90 sows. Loss of BF was greater for P90 sows than for P40 sows during lactation, with H40 sows being intermediate and not significantly different from sows in the two other treatment groups. During lactation, 80%, 15% and 36% of P90, P40, and H40 sows lost weight and 93%, 69% and 79% of P90, P40, and H40 sows lost BF, respectively. From breeding to weaning, increases in BW and BF, as well as in protein mass and fat mass, were lower for H40 sows than for P90 and P40 sows. At weaning, almost all sows had lost BF relative to their BF at the time of insemination (87%, 92% and 92% for P90, P40, and H40 sows, respectively). None of the P90 and P40 sows lost weight during the period from breeding to weaning, whereas 15% of H40 sows lost weight.

## Reproductive performance

The number of TPB and the number of weaned piglets did not differ significantly among treatments (Table 3). The average BW and BMI of piglets at L1 were higher for the P90 than for the P40 treatment (*P* = 0.003 and *P* = 0.024, respectively). The percentage of piglets weighing less than 1 kg was lower in P90 litters than in P40 litters (*P* = 0.002), whereas the percentage of piglets weighing more than 2 kg was higher in P90 litters than in H40 litters (*P* = 0.046) and tended to be higher in P90 litters than in P40 litters (*P* = 0.051). The CV of birth weight also tended to differ among treatments, with litters of P40 sows tending to have greater within-litter birth weight variation relative to H40 sows (*P* = 0.076). At weaning, total litter weight was not different

between treatments, but piglets from the P90 treatment were heavier than piglets from the H40 treatment (*P* = 0.049) and had a higher average daily gain (*P* = 0.045).

## Sow behaviour

Percentage of time spent standing during 24-h periods did not differ among treatments at weeks 8–9 of gestation, whereas it differed at weeks 12–13 and tended to differ at week 15 of gestation, with lower values for P90 sows (Table 4). Percentage of time spent standing in the pasture during daytime tended to differ between the P90 and P40 sows at weeks 8–9 of gestation and was significantly different at weeks 12–13, and 15 of gestation, again with lower values for P90 sows.

## Estimated forage intake

Hay intake of H40 sows, when measured on the basis of amounts offered and refused, increased linearly during gestation (*P* < 0.001; Fig. 4). The treatments significantly (*P* = 0.049) affected the estimated total forage intake from week 5 of gestation to farrowing. The forage DM intake of P40 sows was greater than that of P90 sows (*P* = 0.041; 1.56 ± 0.129 vs. 1.02 ± 0.127 kg DM/sow/d). Forage intake of H40 sows (1.26 ± 0.129 kg DM/sow/d) was intermediate but not significantly different from that of P90 and P40 sows. According to the model used, average daily ME intake from both concentrate feed and forages, from week 5 of gestation to farrowing, differed among treatments (*P* < 0.001). Daily ME intake of P90 sows (42.8 ± 1.4 MJ ME/d) was higher than that of P40 sows (32.5 ± 1.4 MJ ME/d; *P* = 0.002) and H40 sows (29.1 ± 1.4 MJ ME/d; *P* < 0.001). Daily ME intake did not differ between P40 and H40 sows (*P* = 0.265). The proportion of total
<caption>**Table 3**</caption>

Reproductive performance (Least square-means) of outdoor gestating sows given 90% of metabolisable energy (ME) requirements from concentrate with access to a pasture plot (P90), 40% of ME requirements from concentrate with access to a pasture plot (P40), and 40% of ME requirements from concentrate with access to a bare paddock and hay ad libitum (H40).

<table><thead><tr><th rowspan="2"></th><th colspan="4">Treatment</th><th rowspan="2">SEM</th><th rowspan="2">P-value</th></tr><tr><th>P90</th><th>P40</th><th>H40</th></tr></thead><tbody><tr><td>Number of litters at L1</td><td>15</td><td>14</td><td>14</td><td></td><td></td><td></td></tr><tr><td>Total piglets born per litter</td><td>14.7</td><td>14.7</td><td>15.6</td><td>1.17</td><td>0.715</td><td>0.092</td></tr><tr><td>Total litter weight at L1 (kg)</td><td>24.0<sup>A</sup></td><td>20.3<sup>B</sup></td><td>23.2<sup>AB</sup></td><td>1.26</td><td>0.054</td><td>0.031</td></tr><tr><td>BMI at L1</td><td>24.0<sup>a</sup></td><td>21.8<sup>b</sup></td><td>22.7<sup>ab</sup></td><td>0.63</td><td>0.004</td><td>0.031</td></tr><tr><td>BW at L1 (kg/piglet)</td><td>1.69<sup>a</sup></td><td>1.44<sup>b</sup></td><td>1.54<sup>ab</sup></td><td>0.054</td><td>0.085</td><td>0.025</td></tr><tr><td>CV of birth weight at L1 (%)</td><td>19.8<sup>AB</sup></td><td>23.0<sup>A</sup></td><td>18.2<sup>B</sup></td><td>1.48</td><td>0.085</td><td>0.002</td></tr><tr><td>Piglets &lt;1 kg at L1 (%)</td><td>3.3<sup>a</sup> [0.7; 7.9]</td><td>18.8<sup>b</sup> [11.4; 27.6]</td><td>5.1<sup>a</sup> [1.5; 10.7]</td><td></td><td></td><td>0.025</td></tr><tr><td>Piglets &gt;2 kg at L1 (%)</td><td>19.2<sup>AA</sup> [9.4; 31.6]</td><td>5.5<sup>abb</sup> [0.8; 14.1]</td><td>5.3<sup>b</sup> [0.7; 13.7]</td><td></td><td></td><td>0.025</td></tr><tr><td>Number of litters at weaning</td><td>15</td><td>14</td><td>12</td><td></td><td></td><td></td></tr><tr><td>Total piglets weaned per litter</td><td>8.73</td><td>8.49</td><td>10.64</td><td>0.86</td><td>0.155</td><td>0.161</td></tr><tr><td>Total litter weight at weaning (kg)</td><td>132.4</td><td>121.9</td><td>149.6</td><td>10.26</td><td>0.155</td><td>0.161</td></tr><tr><td>BW at weaning (kg/piglet)</td><td>15.26<sup>a</sup></td><td>14.86<sup>ab</sup></td><td>13.21<sup>b</sup></td><td>0.86</td><td>0.048</td><td>0.048</td></tr><tr><td>Average daily gain (g/d/piglet)</td><td>379<sup>a</sup></td><td>368<sup>ab</sup></td><td>328<sup>b</sup></td><td>21</td><td>0.047</td><td>0.047</td></tr></tbody></table>

L1 = day 1 of lactation; BMI = Body Mass Index (calculated as: BMI = $\frac{\text{birth weight}}{(\text{crown}-\text{rump length})^2}$).

Values in [ ] correspond to the lower and upper limits of the back-transformed confidence interval.

a,b Within a row, values with different superscript small letters differ significantly at *P* < 0.05.

A,B Within a non-significantly different pair, average values with different superscript capital letters tended (0.05 ≤ *P* < 0.1) to be different.

<caption>**Table 4**</caption>

Percentage of time spent standing in the pasture over 24 h or during daytime during gestation (Least square-means) of outdoor gestating sows given 90% of metabolisable energy (ME) requirements from concentrate with access to a pasture plot (P90), 40% of ME requirements from concentrate with access to a pasture plot (P40), and 40% of ME requirements from concentrate with access to a bare paddock and hay ad libitum (H40).

<table><thead><tr><th rowspan="2"></th><th colspan="3">Treatment</th><th rowspan="2">SEM</th><th rowspan="2">Treatment effect<br/>P-value</th></tr><tr><th>P90</th><th>P40</th><th>H40</th></tr></thead><tbody><tr><td>Number of replicates<sup>a</sup></td><td>5</td><td>5</td><td>5</td><td></td><td></td></tr><tr><td>Time spent standing over 24 h (%)</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Weeks 8–9</td><td>23.0<sup>a</sup></td><td>23.6<sup>a</sup></td><td>25.5<sup>a</sup></td><td>1.49</td><td>0.465</td></tr><tr><td>Weeks 12–13</td><td>22.9<sup>aA</sup></td><td>30.7<sup>b</sup></td><td>27.0<sup>abB</sup></td><td>1.87</td><td>0.005</td></tr><tr><td>Week 15</td><td>23.6<sup>A</sup></td><td>31.1<sup>B</sup></td><td>29.1<sup>AB</sup></td><td>1.91</td><td>0.051</td></tr><tr><td>Time spent standing at pasture during daytime (%)</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Weeks 8–9</td><td>16.2<sup>A</sup></td><td>20.7<sup>B</sup></td><td>–</td><td>3.24</td><td>0.065</td></tr><tr><td>Weeks 12–13</td><td>19.2<sup>a</sup></td><td>29.0<sup>b</sup></td><td>–</td><td>3.12</td><td>0.001</td></tr><tr><td>Week 15</td><td>20.4<sup>a</sup></td><td>34.1<sup>b</sup></td><td>–</td><td>2.24</td><td>0.006</td></tr></tbody></table>

† The statistical unit was a group of three sows.

a,b Within a row, values with different superscript small letters differ significantly at *P* < 0.05.

A,B Within a non-significantly different pair, values with different superscript capital letters tended (0.05 ≤ *P* < 0.1) to be different.

<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Evolution of the average daily hay intake (g DM/sow/day) during gestation of outdoor gestating sows (n = 5 groups of three sows) with access to a bare paddock and hay provided *ad libitum* (H40 treatment: concentrate providing 40% of metabolisable energy (ME) requirements and access to a bare paddock and hay *ad libitum*). Week of gestation had a significant effect on hay intake (*P* < 0.001).</figcaption></figure>

ME intake from forage also differed among treatments (*P* < 0.001). The proportion of total ME intake from forage was lower for P90 (25.1 ± 2.3% of total ME intake) sows than for P40 (51.4 ± 2.3%; *P* < 0.001) and H40 (46.0 ± 2.3%; *P* < 0.001) sows. The proportion

of total ME intake from forage did not differ between P40 and H40 sows (*P* = 0.282).

## Discussion

This study shows that concentrate feeding level and type of forage influence the performance and behaviour of outdoor gestating sows.

### Sow body condition and behaviour during gestation

The lower BW and BF observed at the end of gestation in sows restricted to obtaining 40% of their ME requirements from concentrate feed indicate that their intake of ME and possibly of other nutrients during gestation was less than that of P90 sows. This is reflected in the estimate of the daily total ME intake. Several studies have shown that BW and BF of sows at the end of gestation are directly related to ME intake and nutrient intake during gestation (Dourmad, 1991; Long et al., 2010). In the present study, the average net maternal gain of P90 sows was 52 kg/sow during gestation, a value greater than those previously reported. Young et al. (2004) reported a gain of 28.3 kg/sow for sows weighing 214 kg at mating, while Dourmad et al. (1996) reported a gain of 46.8 kg/sow for sows weighing 201 kg at mating and fed a standard diet. At
farrowing, P90 sows had a BF of approximately 20 mm, which is within the range of BF values considered ideal to maximise performance according to Dourmad et al. (2001) and Zhou et al. (2018). Therefore, it seems that the intake of ME and nutrients of P90 sows during gestation was more than enough to satisfy ME requirements.

During gestation, 80% of P90 sows had an increase in BF, whereas almost all P40 and H40 sows had a decrease. The gain in estimated fat mass was negative or close to zero in P40 and H40 sows, whereas P90 sows had an increase of about 13 kg in estimated fat mass. This result suggests that the ME intake of sows whose concentrate intake was restricted to 40% of requirements during gestation was not sufficient and led to a reduction in relative fat mass in maternal tissues. During gestation, P40 and H40 sows had, on average, a decrease in BF but gained weight, suggesting that protein accretion in maternal tissues (excluding conceptus) occurred but fat deposition was limited. This suggests that for P40 and H40 sows, the ME supply was probably the first factor limiting the growth of the sow.

P40 sows spent more time standing at pasture and they grazed for almost 99% of the time (Aubé et al., 2021). The estimation of forage intake also suggests a greater nutrient intake from forage in P40 than P90 sows. Forage being the only other source of nutrients, these results indicate that P40 sows tried to compensate for reduced concentrate feed intake by obtaining additional nutrients through pasture feeding. This disagrees with the results of Rivera Ferre et al. (2001), who found no systematic difference in forage intake for sows fed either 3 kg or 1.5 kg of concentrate feed. However, in that experiment, feed restriction was applied for only 2 weeks, which may explain the lack of a significant effect. In contrast, Santos Ricalde and Lean (2006) found that DM intake of fresh star grass increased as energy from concentrate feed decreased, with sows fed at 70% of requirements consuming 22% more forage than sows fed at 100%. However, this consumption of forage was insufficient to reach the same total energy intake, probably due to the bulking effect of the fibre that may have limited the forage intake capacity of sows.

In the present study, forages had a relatively high concentration of neutral detergent fibre (NDF; 45–49%), a situation that may have limited the sows' forage intake. Furthermore, the sows' first contact with forages occurred at week 5 of gestation. Sappok et al. (2015) estimated that it takes longer than 19 days for sows' large intestinal microbiota to adapt to a high-fibre diet. Therefore, it is possible that the sows' intake of nutrients from forage was not optimal during the first weeks of the experiment, which appears to be borne out by the constant increase in hay intake by H40 sows (Fig. 4). Earlier habituation of sows to forage might have helped increase forage intake and/or sows' capacity to use the fibrous component as a nutrient source.

## Limitations of forage intake estimation methodology

Forage intake estimates calculated from the performance of the sows fell within the range of values obtained in previous studies with gestating sows. On a ryegrass/clover pasture, Rivera Ferre et al. (2001) reported daily voluntary forage intake of 1.1 kg and 1.5 kg organic matter (OM) per sow in spring and summer, respectively. Assuming that the average ash concentration of the forage across all sampling dates was 120 g/kg DM, forage intake in the present study was approximately 0.9 and 1.4 kg OM/sow/d for P90 and P40 sows, respectively. In the study by Sehested et al. (2004) with a clover/grass pasture, forage intake was estimated at 2.0–2.5 kg OM/sow/d.

Nevertheless, estimation of forage intake from the performance of sows presents certain limitations. First of all, energy was considered as the first limiting factor as the forage had a greater protein

to energy ratio than concentrate feed. It is, however, possible that some amino acids from forage proteins were not available and, hence, limiting. Moreover, nutrient requirements related to outdoor housing were probably underestimated. For example, the activity of sows, which influences energy requirements (Dourmad et al., 2008), was estimated by the time spent standing but it did not take locomotion into account. Furthermore, it is possible that, in the present study, the actual lower critical temperature (LCT) was higher for P40 and H40 than P90 sows because LCT decreases with increasing feed level (Verhagen et al., 1986), resulting in underestimated energy requirements for sows fed at 40%. Nevertheless, in the present study, the same LCT was considered for all sows in the calculation of forage intake (20 °C, as suggested by Dourmad et al., 2008). Moreover, daily average temperatures were used to determine the extra energy requirement for maintenance (if below the LCT). As presented in the Supplementary Material, the temperature at any given point ranged from –1.5 to 31.6 °C (Supplementary Table S1), meaning that sows experienced some periods well below their LCT and also other periods with high temperatures which might have decreased their feed intake. Unfortunately, it was not possible to take all these climatic variations into account in the calculation. As Decruyenaere et al. (2009) pointed out, when forage intake is estimated on the basis of animal performance and requirements, the main difficulty lies in estimating true animal requirements, specifically in outdoor conditions.

Furthermore, the forage intake estimation was based on the average forage energy concentration and did not take into account the existence of selective grazing, which was demonstrated by Sehested et al. (2004). Additionally, it is possible that sows consumed roots and/or organisms from the soil, leading to an overestimation of the ingested energy attributed to forage. Finally, the estimates of hay intake from sows' performance were twice as high as those obtained from weighing hay refusals (1.26 vs. 0.524 kg DM/sow/d on average, respectively). The reason for this discrepancy remains unknown and further investigations are needed to understand why these two methods gave such different results. Nevertheless, it should be mentioned that the DM concentration of hay refusals was not measured, which could have led to an underestimation of hay intake owing to the humidity in the environment and/or sows' saliva.

## Reproductive performance

Although litter size was not affected by treatment, an effect on piglet birth weight was observed. Piglets of P40 sows were lighter at birth than piglets of P90 sows, with piglets of H40 sows being intermediate in weight. The treatments were not expected to affect litter size at birth because feed restriction only began at week 5 of gestation. After week 4 of gestation, the level of energy supplied to sows has little effect on litter size (Kongsted, 2005). The lower piglet weight and BMI of P40 sows indicate that the nutrient supply was insufficient to fully support foetal development at the end of gestation. Despite the fact that sows are able to mobilise maternal nutrient reserves to support foetal development, foetal growth can be impaired under severe feed restriction (Campos et al., 2012). Zhou et al. (2018) found that sows with low BF (≤16 mm) at the end of gestation had piglets with lower birth weight and a higher proportion of small piglets (<800 g) compared to sows with a BF of 19–20 mm, but the BF of the sows did not affect litter size. This is consistent with our results showing that P90 sows with a BF of 20 mm had piglets with a greater average birth weight and a lower proportion of small piglets than P40 sows with a lower BF (≈17 mm) at the end of gestation. In addition, the BF of H40 sows at farrowing (≈16 mm) was well below the ideal BF range. No significant difference was observed between the birth weight of
piglets from P90 and H40 sows. The percentage of heavy piglets, however, was higher for P90 sows than for H40 sows. Therefore, feed restriction appears to have had a lesser effect on foetal growth in H40 sows than in P40 sows, despite the fact that sows in both treatments showed similar body condition across the gestation period. Moreover, P40 sows had a higher proportion of small piglets (<1 kg) and a higher within-litter birth weight variation than H40 sows. The development of the mammary gland during gestation might have been affected by the feeding treatments but the present study does not allow for the quantification of this effect. The difference observed between P40 and H40 sows' reproductive performance suggests that nutrient partitioning may have been more directed towards maternal tissues than towards conceptus in P40 sows compared to H40 sows, perhaps because of a higher maintenance requirement in P40 sows due to walking during grazing (Lachica and Aguilera, 2000; Edwards, 2003).

## Changes in sow body condition during lactation

During lactation, decreases in BF, BW and fat mass and protein mass were greater for P90 sows than for P40 and H40 sows. On the other hand, piglets' growth was higher for the P90 treatment than the H40 treatment, leading to heavier individual piglets at weaning but no significant difference in litter weight. This indicates that, during lactation, P90 sows mobilised their body reserves to a greater extent than P40 and H40 sows. Changes in sow BW and backfat during lactation are the results of feed intake and milk production, while piglets' growth is the result of their intake of milk along with that of concentrate feed and other nutrients. Because the feed intake of sows and piglets during lactation were not measured in the present study, it is difficult to conclude if the observed treatment differences in body condition throughout lactation are due to a greater feed intake by P40 and H40 sows relative to P90 sows during lactation or to a lesser milk production. At weaning, P90 and P40 sows had similar weight and BF, indicating that the balance between feed intake and milk production of P40 sows allowed them to compensate for the deficit during gestation. In contrast, H40 sows had lower BW and tended to have lower BF at weaning than P90 sows, indicating that, despite their greater BF and BW gains during lactation, they were not able to fully compensate for the restriction during gestation. Piglets' data at weaning suggest that P40 piglets' performance was not compromised, since no significant difference was found between P90 and P40 piglets regarding weaning weight and average daily gain. However, it is difficult to consider that piglets' performance in lactation reflects solely the sows' milk production since piglets may have found other sources of energy such as sow concentrate feed and forage. Therefore, the performance of P40 piglets could also be due to their ability to transition quickly from milk to solid food. Considering both the sows' body condition as well as litter weight and size at weaning, P90 and P40 sows performed similarly. However, these results would need to be confirmed on a larger number of animals.

Considering the overall performance from breeding to weaning, the losses of BF, fat mass, and protein mass were lower for P90 and P40 sows than for H40 sows, and P90 and P40 sows gained more weight than H40 sows. Both P90 and P40 sows had a BF of approximately 14 mm at weaning, whereas H40 sows had a BF of 11 mm, which is considered too low. A higher culling rate (Young et al., 1991) and a longer weaning to breeding interval (Dourmad et al., 2001) have been reported in sows with a BF of less than 12 mm at weaning. In the context of a 5-week lactation duration that would put some pressure on sows' energy stores to maintain milk production, gestation feeding restriction did not affect final sows' body condition the same way in P40 and H40 sows, with H40 sows

exhibiting a poor body condition that could impair future reproductive performance.

## Conclusion

Sows fed concentrates at 40% of their ME requirements during gestation did not consume enough fresh forage from pasture or hay to compensate for the restriction in energy intake. This level of concentrate feed reduction may be excessive for outdoor gestating sows under the conditions of the present experiment. Nevertheless, sows fed at 40% of ME requirements with access to pasture, and subsequently fed concentrates *ad libitum* during lactation, reached a body condition at weaning (i.e. at 5 weeks of lactation) that was similar to that of sows fed concentrate at 90% of ME requirements during gestation, whereas sows fed at 40% with access to hay did not. Therefore, pasture access may be more effective than provision of hay for increasing subsequent feed intake during lactation as long as the quality and quantity of forage available is good enough. Sows fed at 40% of their ME requirements with access to pasture most likely increased their forage intake to compensate for the feed reduction. However, the nutritional contribution of the forage during gestation was insufficient, either because of insufficient voluntary intake and/or insufficient ability of the sows to utilise the fibrous components of the forage. On the other hand, a concentrate feed reduction of 10% was easily compensated through forage intake, suggesting that feed restriction could be further increased without impairing the performance of outdoor gestating sows. Taking into account the relatively high crude protein and low energy concentration of forages, a potential way to improve the energy balance would be to provide more energy-rich concentrates to gestating sows partially fed with forages.

## Supplementary material

Supplementary data to this article can be found online at
https://doi.org/10.1016/j.animal.2021.100346.

## Ethics approval

The Institutional Animal Care Committee of the Sherbrooke Research and Development Centre of Agriculture and Agri-Food Canada (QC, Canada) approved the procedures (authorisation #523) in conformity with the guidelines of the Canadian Council on Animal Care (CCAC, 2009) and the Canadian code of practice (NFACC, 2014).

## Data and model availability statement

Data and models used for the purpose of this study are not deposited in an official repository. The data that support the study findings can be made available upon request.

## Author ORCIDs

L. Aubé: https://orcid.org/0000-0002-6174-3743

R. Bergeron: https://orcid.org/0000-0001-7757-2531

S.A. Edwards: https://orcid.org/0000-0002-8890-0112

N. Devillers: https://orcid.org/0000-0002-5866-9394

## Author contributions

L. Aubé: Methodology, Investigation, Formal analysis, Writing - Original Draft and making subsequent revisions
**F. Guay:** Conceptualization, Methodology, Formal analysis, Writing - Review & Editing, Supervision

**R. Bergeron:** Conceptualization, Methodology, Writing - Review & Editing

**G. Bélanger:** Conceptualization, Writing - Review & Editing

**G.F. Tremblay:** Conceptualization, Resources, Writing - Review & Editing

**S.A. Edwards:** Conceptualization, Writing - Review & Editing

**J.H. Guy:** Conceptualization, Writing - Review & Editing

**N. Devillers:** Conceptualization, Methodology, Investigation, Resources, Writing - Review & Editing, Funding acquisition, Supervision, Project administration

## Declaration of interest

None.

## Acknowledgements

The authors thank Marjolaine St-Louis, Sandra Lebon, Korentin Boutoux, France Champagne, Étienne Lauzier-Hudon and Geneviève Bégin for their invaluable technical assistance, the staff of the swine complex for taking care of the animals, the field crop staff for pasture and paddock management, Steve Méthot for help with statistical analyses and Jean-Pierre Charuest for his support.

## Financial support statement

This work was supported by Agriculture and Agri-Food Canada within the Canadian Agriculture Partnership (Project ID: J-001357).

## References

Aubé, L., Guay, F., Bergeron, R., Bélanger, G., Tremblay, G.F., Edwards, S., Guy, J., Théau, J., Devillers, N., 2018. Nutritional value of pasture and dry-forage, and foraging behaviour in outdoor gestating sows. In: Proceedings of the 52nd Congress of the International Society for Applied Ethology, 30 July–03 August 2018, Charlottetown, Prince Edward Island, Canada, p. 240.

Aubé, L., Guay, F., Bergeron, R., Bélanger, G., Tremblay, G.F., Devillers, N., 2019. Sows' preferences for different forage mixtures offered as fresh or dry forage in relation to botanical and chemical composition. Animal 13, 2885–2895.

Aubé, L., Guay, F., Bergeron, R., Théau, J., Devillers, N., 2019. Foraging behaviour of gestating sows on pasture and damages to vegetation cover are influenced by restriction of concentrate feed. Applied Animal Behaviour Science 237, 105299.

Campos, P.H.R.F., Silva, B.A.N., Donzele, J.L., Oliveira, R.F.M., Knol, E.F., 2012. Effects of sow nutrition during gestation on within-litter birth weight variation: a review. Animal 6, 797–806.

CCAC, 2009. Guidelines on: The Care and Use of Farm Animals in Research, Teaching and Testing. Canadian Council on Animal Care, Ottawa, Ontario, Canada.

Decruyenaere, V., Buldgen, A., Stilmant, D., 2009. Factors affecting intake by grazing ruminants and related quantification methods: a review. Biotechnology, Agronomy, Society and Environment 13, 559–573.

Dourmad, J.Y., 1991. Effect of feeding level in the gilt during pregnancy on voluntary feed intake during lactation and changes in body composition during gestation and lactation. Livestock Production Science 27, 309–319.

Dourmad, J.Y., Etienne, M., Noblet, J., 2001. Measuring backfat depth in sows to optimize feeding strategy. INRA Productions Animales 1, 41–50.

Dourmad, J.Y., Etienne, M., Noblet, J., Causeur, D., 1997. Prediction of the chemical composition of reproductive sows from their body weight and backfat depth-Utilization for determining the energy recordance. Journées de la Recherche Porcine en France 29, 255–262.

Dourmad, J.Y., Etienne, M., Valancogne, A., Dubois, S., van Milgen, J., Noblet, J., 2008. InraPorc: A model and decision support tool for the nutrition of sows. Animal Feed Science and Technology 143, 372–386.

Dourmad, J.Y., Etienne, M., Noblet, J., 1996. Reconstitution of body reserves in multiparous sows during pregnancy: effect of energy intake during pregnancy and mobilization during the previous lactation. Journal of Animal Science 74, 2211–2219.

Edwards, S.A., 2003. Intake of nutrients from pasture by pigs. Proceedings of the Nutrition Society 62, 257–265.

Eriksen, J., Studnitz, M., Strudsholm, K., Kongsted, A.G., Hermansen, J.E., 2006. Effect of nose ringing and stocking rate of pregnant and lactating outdoor sows on exploratory behaviour, grass cover and nutrient loss potential. Livestock Science 104, 91–102.

Hales, J., Moustsen, V.A., Nielsen, M.B.F., Hansen, C.F., 2013. Individual physical characteristics of neonatal piglets affect preweaning survival of piglets born in a noncrated system. Journal of Animal Science 91, 4991–5003.

Honeyman, M., Roush, W., 1999. Supplementation of midgestation swine grazing alfalfa. American Journal of Alternative Agriculture 14, 103–108.

Kongsted, A.G., 2005. A review of the effect of energy intake on pregnancy rate and litter size-discussed in relation to group-housed non-lactating sows. Livestock Production Science 97, 13–26.

Lachica, M., Aguilera, J., 2000. Estimation of the energy costs of locomotion in the Iberian pig (Sus mediterraneus). British Journal of Nutrition 83, 35–41.

Long, H., Ju, W., Piao, L., Kim, Y., 2010. Effect of dietary energy levels of gestating sows on physiological parameters and reproductive performance. Asian-Australasian Journal of Animal Sciences 23, 1080–1088.

Muñoz Castillo, C.H., Magaña-Magaña, M.Á., Lara-Lara, P.E., Ugalde, J.P.R., Ortiz Ortiz, J.R., Sanginés-García, J.R., 2011. Productive behavior of pregnant sows supplemented with *Morus alba*. Zootecnia Tropical 29, 273–282.

NFACC, 2014. NFACC code of practice development process. National Farm Animal Care Council (NFACC), Lacombe, AB, Canada.

Noblet, J., Perez, J., 1993. Prediction of digestibility of nutrients and energy values of pig diets from chemical analysis. Journal of Animal Science 71, 3389–3398.

Noblet, J., Shi, X.S., 1993. Comparative digestibility of energy and nutrients in growing pigs fed ad libitum and adults sows fed at maintenance. Livestock Production Science 34, 137–152.

Park, H.S., Min, B., Oh, S.H., 2017. Research trends in outdoor pig production – A review. Asian-Australasian Journal of Animal Sciences 30, 1207–1214.

Rachuonyo, H., Allen, V., McGlone, J., 2005. Behavior, preference for, and use of alfalfa, tall fescue, white clover, and buffalograss by pregnant gilts in an outdoor production system. Journal of Animal Science 83, 2225–2234.

Ringgenberg, N., Bergeron, R., Devillers, N., 2010. Validation of accelerometers to automatically record sow postures and stepping behaviour. Applied Animal Behaviour Science 128, 37–44.

Rivera Ferre, M., Edwards, S., Mayes, R., Riddoch, I., Hovell, F.D., 2001. The effect of season and level of concentrate on the voluntary intake and digestibility of herbage by outdoor sows. Animal Science 72, 501–510.

Santos Ricalde, R.H., Lean, I.J., 2002. Effect of feed intake during pregnancy on productive performance and grazing behaviour of primiparous sows kept in an outdoor system under tropical conditions. Livestock Production Science 77, 13–21.

Santos Ricalde, R.H., Lean, I.J., 2006. Digestibility of dried star grass (Cynodon nlemfuensis) and consumption of fresh star grass in primiparous pregnant sows. Animal Feed Science and Technology 129, 12–22.

Sappok, M.A., Perez Gutierrez, O., Smidt, H., Pellikaan, W.F., Verstegen, M.W.A., Bosch, G., Hendriks, W.H., 2015. Adaptation of faecal microbiota in sows after diet changes and consequences for in vitro fermentation capacity. Animal 9, 1453–1464.

Sehested, J., Søegaard, K., Nielsen, V., Roeorstoff, A., Monrad, J., 2004. Grazing with heifers and sows alone or mixed: Herbage quality, sward structure and animal weight gain. Livestock Production Science 88, 223–238.

Théau, J., Lauzier-Hudon, É., Aubé, L., Devillers, N., 2021. Estimation of forage biomass and vegetation cover in grasslands using UAV imagery. Plos One 16, e0245784.

Verhagen, J., Verstegen, M., Geuyen, T., Kemp, B., 1986. Effect of environmental temperature and feeding level on heat production and lower critical temperature of pregnant sows. Journal of Animal Physiology 55, 246–256.

Young, L., King, G., Shaw, J., Quinton, M., Walton, J., McMillan, I., 1991. Interrelationships among age, body weight, backfat and lactation feed intake with reproductive performance and longevity of sows. Canadian Journal of Animal Science 71, 567–575.

Young, M.G., Tokach, M.D., Aherne, F.X., Main, R.G., Dritz, S.S., Goodband, R.D., Nelssen, J.L., 2004. Comparison of three methods of feeding sows in gestation and the subsequent effects on lactation performance. Journal of Animal Science 82, 3058–3070.

Zhou, Y., Xu, T., Cai, A., Wu, Y., Wei, H., Jiang, S., Peng, J., 2018. Excessive backfat of sows at 109 d of gestation induces lipotoxic placental environment and is associated with declining reproductive performance. Journal of Animal Science 96, 250–257.