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Scientific Reports Volume 11, Article Number: 16380 (2021) Cite this article

The grower-growth stage accounts for 64% of the total water used by the farm herd. Part of it is consumed by pigs, but part of it is wasted. The use and waste of drinking water are affected by different factors. We investigated how different population sizes and different levels of enrichment affect the water consumption (intake plus waste), water waste, behavior, and performance of growing-finishing pigs. The experiment used 11-week-old (77 ± 2 days) pigs (n = 672). Effect of group size: small (12 pigs), medium (24 pigs) and large (48 pigs) through two enrichment levels (low-wooden posts, hanging rubber toys, high-the same as low fresh grass) Evaluation. Group size has no effect on water use or waste. Pigs with high enrichment (10.4 ± 0.4 L/pig/day) consume less water than those with low enrichment (11.0 ± 0.4 L/pig/day; p <0.001). The water waste/drinkers/hour of high-enrichment fences was lower than that of low-enrichment fences (p = 0.003). The number of drinking (p = 0.037) and total occupancy per hour (p = 0.048) were also higher for pens with low concentration than high concentration. In large groups and highly enriched fences, aggressive and harmful behaviors are less. Therefore, the high enrichment allowance reduces water use and waste, and therefore may be good for the environment and animal welfare.

As the world’s population and income increase, the global demand for meat products may increase1. This may lead to a surge in demand for pork, which is one of the most consumed meats in the world. Pig production already accounts for 19% of the global water footprint of farm animal production3. This means that each ton of pork3 requires approximately 6000 cubic meters of water, of which 70% is used for off-farm feed production, 24% is used for farm drinking, cleaning and feed mixing, and 6% is used for slaughter4. Due to the limited global supply of fresh water, it is important to optimize water use in the pig production chain.

The provision of adequate drinking water is considered to be the basis for ensuring good welfare in the livestock industry. In pig production, drinking water accounts for 80-87% of the total farm water consumption5,6, while the growth-finishing stage accounts for 64% of the total water consumption of the pig herd5. At this stage, the amount of drinking water used is 1.9 to 6.8 liters/pig/day7. Part of this water is indeed consumed by pigs, but part of it is wasted. In addition to affecting freshwater resources, water waste will increase the volume of mud, thereby diluting nutrients. This increases operating costs (ie, the cost of manure treatment and disposal) and is therefore another reason to minimize water waste.

The use and waste of drinking water and the ratio between the two are affected by pigs (e.g. weight, social competition, feed intake)8,9, environment (e.g. temperature, humidity)10 and management factors (e.g. drinking fountain type, pen design ) 7,8,11. An important factor affecting drinking behavior is resource allowances. Researchers found that in 24 hours, 10 growing pigs in each group visited single nipple drinkers more than 312 groups at night. It is speculated that this is due to a higher percentage of interrupted visits during the day, because there may be more competition for drinking fountains in larger groups during periods when pigs are usually active. Group size seems to affect water use and drinking behavior; this was also found in a study where pigs in groups of 20 had more contact with water drinkers (more visits to water drinkers, longer drinking time), But pigs in the 608,13 group use less drinking water. When the stocking density remains the same, larger groups of pigs have more shared space per pig, which can provide them with a more complex and attractive environment. The impact of this on drinking behavior has not been fully explored, but it may be that more shared space leads to less contact with drinkers, thereby reducing waste, because pigs have a larger exploration area.

These results also indicate that pigs do not seem to use drinking fountains purely for drinking8,13. The poor environment in which pigs usually live can also promote the performance of redirection (foraging) behavior. This can manifest itself as playing with drinkers9,14, leading to wastage of water resources. Providing appropriate environmental abundance can reduce the occurrence of such negative behaviors15, thereby potentially reducing water waste. Comparing the use of a series of enriched materials suitable for slat systems, it is found that the loose materials provided in the shelves are more favored by pigs than point source items (such as wooden chew sticks, rubber toys, etc.)16. Regarding the types of materials provided on the shelves, pigs prefer fresh grass or silage to straw. Silage allows pigs to take longer,17 and uses 15 grams more fresh grass per day than straw.

In order to reduce water waste, it is necessary to understand drinking behavior and the related water waste. Although we know that at all stages of production, growing and finishing pigs consume most of the total farm water consumption, and some studies have focused on the water consumption of growing and finishing pigs 7,8,11,12,13,18,19 The focus of no research is The influence of group size and the influence of abundance on drinking behavior and the water wasted by drinkers. Therefore, the purpose of this study is to investigate how different group sizes and different levels of enrichment affect the water consumption (intake plus waste), water waste, behavior and performance of growing-finishing pigs. We assume that a larger group size and the provision of beneficial concentrated materials will optimize water use by reducing waste.

The study was conducted at the Teagasc Pig Research Institute in Ireland, an experimental pig unit with a herd of 200 sows. The experiment was carried out from July 2019 to April 2020, and was approved by the Teagasc Animal Ethics Committee (TAEC233-2019); all procedures are in accordance with Irish legislation (SI no. 543/2012) and the EU Animal Experiment Directive 2010/63/ EU proceeded.

The experiment included 672 pigs [Denmark Duroc × (Large White × Landrace)]. Between weaning (4 weeks of age) and the beginning of the experiment (11 weeks of age; 77 ± 2 days), pigs were managed in 12 weaning pig houses (2.4 m × 2.6 m). The experiment was repeated three times in one room. The room contains 4 enclosures for each experimental group size: small (4.2 m × 2.5 m; 12 pigs), medium (5.0 m × 4.2 m; 24 pigs) and large (8.2 m × 5.0 m; 48 pigs) , Provide a space allowance of 0.86 square meters per pig in all treatments (the room layout in Supplementary Material S1). There are also two hospital pens in the room, the same size as the pen used for SMALL treatment.

Through a single-space wet/dry feeder with built-in teats, the pigs are fed ad libitum with standard pellet feed (43.5% wheat, 30% corn, 17.1% soybean-HIpro, 7.1% soybean hulls). Pigs can mix water and feed in the trough as needed. A computerized feeding system (BigFarmNet Manager, Big Dutchman Ltd. v3.1.5.51039, Calveslage, Vechta, Germany) was used to record the feed intake of each feeder. Each fence also has a separate nipple, located in a bowl-shaped drinker installed 35 cm above the ground and 30 cm from the wet and dry feeder. Small pig houses have 1 feeder and 1 separate drinker, medium pig houses have 2 feeders and 2 separate drinkers, and large pig houses have 4 feeders and 4 separate drinkers. , To ensure that the number of pigs in each waterer and feeder is the same in each barn. All the fences are fully slatted concrete floors, the rooms are mechanically ventilated, and there is a roof fan in the center of the room, providing artificial light for 8 hours a day. The average room temperature is kept at 20 °C.

The experiment uses a 3×2 factorial design. Evaluate the effect of group size (small, medium, large) across two enrichment levels (high and low). The pigs in the LOW enrichment area received a wooden pole and a hanging rubber toy/12 pigs. The pigs in the HIGH enrichment area also received the same result, adding a shelf/12 pigs, which was filled with fresh grass and fixed to the wall of the fence. Before pigs enter, all enclosures are equipped with bacteria-enhancing materials.

One day before the start of the experiment, the pigs were individually weighed, and then the individual weights in each weaned pen were added. For the SMALL treatment, 6 pigs from two independent weaning pens were mixed together. For the MEDIUM treatment, two weaning pens are mixed, for the LARGE treatment, 4 weaning pens are mixed. The final overall average pen weight is 33.8 ± 3.6 kg. In each final group there are the same number of boars and sows. In Ireland, boars and sows are kept in the same circle, which is a common practice on commercial farms in Ireland. In Ireland, whole boars are produced, so the slaughter weight is lower to avoid boar odor problems.

A total of 24 pens were used throughout the experiment, 12 pens were repeated for the first time, and 6 pens were repeated for the second and third times. The first repeat has 2 fences for each group size and enrichment combination (for example, 2 small fences with low enrichment, 2 medium fences with low enrichment, 2 small fences with high enrichment, 2 high Enriched middle fence, etc.). In the second and third repetitions, we include 1 pen for each group size and concentration combination (e.g., 1 small pen with low concentration, 1 medium pen with low concentration, 1 small pen with high concentration , 1 highly concentrated medium pen, etc.). Due to the scarcity of pigs available to participate in the study. Reuse 2 and 3 separate halves of the room in order to use all pens twice throughout the experiment.

Use a data logger (Tinytag, Sussex, UK) to record daily measurements of temperature and humidity (every 15-minute recording interval). The logger is installed in a room 2 m above the floor. All data loggers are installed in the channels of the room, each channel has 2 data loggers. Six data loggers were repeatedly installed for the first time, and four data loggers were repeatedly installed for the second and third times. Before starting the experiment, use an illuminance meter (ISO-TECH, ILM 1337 Light Meter, UK) to measure the light intensity of each fence (in front of the drinker).

The wood and hanging rubber toys were weighed at the beginning and end of the experiment to estimate the wear rate of the pigs. Loose freshly cut grass (10-20 cm long) is added to the racks at a ratio of 90 g/head, and refilled when the quantity drops below half of the total allowable amount per rack, as described previously16.

At the beginning of the experiment, the water flow of each nipple drinker was measured. Collect the water in a plastic bag for 30 seconds and measure the volume using a 1000 ml graduated cylinder. The average water flow rate is 1.47 ± 0.14 L/30 s (average ± sd). All the fences are equipped with water meters, and each one covers a wet/dry feeder and a bowl drinker next to it. Water consumption is monitored by an automatic online water monitoring system (Carlo Gavazzi Automation, Italy). Data is recorded every 15 minutes.

In order to record the water wasted by each drinking fountain, a wooden box (0.9 × 0.43 × 0.22 m) was designed (Supplementary materials l S2, S3). The box is surrounded by a waterer and has an opening (0.25 m wide × 0.35 m high) through which pigs can enter the waterer. The opening is located 0.35 m above the ground, allowing unrestricted access to the drinking fountain. Use a container (3.6 liter capacity) placed inside the box and below the drinking fountain to collect the overflowing water from each drinking fountain. The container is comfortably installed on both sides of the box; therefore, any waste water will not flow from the sides of the container and between the boxes. Escape from time to time. Starting from 5 days after the pig moved into the pen (ie 82 ± 2 days old), the amount of waste water was measured 1 day per week for 6 weeks. Once a week (Monday), between 0930 and 1600 hours, use a 1000 ml graduated cylinder to measure the amount of water in the container at least once an hour, if necessary, more frequently.

Starting one week after moving the pigs into the pen (84±2 days), directly observe the behavior of the pigs every week (Wednesday). The first two repeated observations were conducted during the entire 9 weeks of the fattening period, but the third repeated observation was only conducted within the first 5 weeks (interrupted due to COVID-19). Observe each fence continuously for 5 minutes at approximately 1000 hours, 1100 hours, 1400 hours, and 1500 hours every day for all occurrences. The observation order of the pen is random at each observation time, so the average observation time for all treatments is similar. We are mainly interested in destructive behavior and the performance of concentrated use, so we use the ethogram in Table 1 to record these behaviors.

On the 25th day of the experiment, when the pig was about 102 ± 2 days old, the camera (2.0MP fixed wide-angle bullet camera with 40 m infrared night vision function (HIKVision, China) was installed directly above the drinking fountain. All cameras were pointed The drinker and each drinker have a separate camera that records continuously for 24 hours. The data is downloaded to a 1 TB hard drive (PC PRO Computers Ltd., Ireland). A preliminary analysis of water use data (from a water meter) indicates that the drinker is at 0800 Used the most between 2000 hours and 2000 hours. One hour of video clips were extracted for each drinker (1000-1100 hours) for observation, and the time from the beginning to the end of the interview was recorded. The occupation of the drinkers and each entry by recording the pig’s head The box around the drinking fountain (the nose disappears in the opening of the box) and the time the head was removed to determine the number of seizures. From these data, the number of seizures, the duration of each seizure, and T calculated per hour Check-in time. There is no record of the pig’s identity or gender.

On the day before the start of the test and at the end of the test period (147 days), the pigs were individually weighed using digital scales (R323, Rinstrum, Langenfeld, Germany), and the average daily gain (ADG) was calculated based on these weights. According to transport to The computer records the feed of each feeder, and calculates the total amount of feed delivered to each pen each day for the test, so as to calculate the average daily feed intake (ADFI) of the pigs in the pen. From this, calculate the average feed conversion ratio (FCR) for each column. Keep records of pigs that withdrew from the trial due to injury, illness, or death.

All data were analyzed using SAS version 9.4 (SAS Institute Inc., Cary, NC, USA). Before analysis, check the data to visualize the distribution (PROC UNIVARIATE). Use the linear mixed model (PROC MIXED) to analyze water (intake plus waste), water waste, animal behavior, drinking behavior, and performance data. All models include group size (ie, small, medium, and large), enrichment level (ie, high and low), days and repetitions, and related interactions (group size * enrichment) as fixed effects, and pens are included as random effects.

Several different water measurements were analyzed. First, the total amount of water delivered through each meter is added to provide the total amount of water delivered to each fence each day. These data were then used for analysis to compare the water consumption of different treatments throughout the experiment. The day is included as a repetitive effect.

After this, a second analysis was carried out, which only considered measurements made between 0930 and 1600 hours on the day the wastewater was measured. In addition to the wasted water, the total water consumption during this period was compared with the water intake (the total waste was less). For some drinkers, the daily wastewater measurement cannot be performed due to the overflow of water from the container. Therefore, the unit of analysis is the drinker, not the pen. The model includes group size (ie small, medium, and large), enrichment level (ie high and low), drinker, week, repetition, and related interactions (group size * enrichment) as fixed effects, while drinkers with pens Included as a random effect. Weeks within the repetition are included as a repetitive effect.

During each recording session, the performance of the aggressive, harmful, and abundance-oriented behaviors of each pen is summarized, and then divided by the number of pigs to calculate the performance/pig/session ratio. Then calculate the average value of all sessions in each recording day for analysis. As before, the model includes group size, enrichment level, week, repetition, and related interactions (group size * enrichment) as fixed effects, and pens are included as random effects. The week within the repeat is included as a repeat effect.

Three parameters of drinking behavior are measured; the number of matches, the duration of each match, and the duration of alcohol consumption per hour. The model of the number of matches and the hourly check-in time includes the drinker in the pen as a repetitive effect. The model for the duration of each round includes each pig visit to the waterer as a repetitive effect.

Animal performance models (ADG, ADFI and FCR) include group size (ie small, medium and large), enrichment level (ie high and low), repetition and related interactions (group size * enrichment) as fixed effects, and select The fence acts as a random effect.

Interaction effects are reported where they occur. Check the residuals graphically to ensure that the assumptions of the analysis are met. For all analyses, statistical significance was established when α ≤ 0.05. In all cases, the Tukey-Kramer least squares mean was used to adjust multiple comparisons to separate treatment means.

The temperature range of repetition 1 is 18.3 to 24.5 °C, the temperature range of repetition 2 is 15.2-26.0 °C, and the temperature range of repetition 3 is 15.8-24.4 °C. The relative humidity range of Repeat 1 is 52.6 to 97.3%, 51.8-94.2% of Repeat 2, and 46.3-91.5% of Repeat 3. The light intensity ranges from 43 to 201 ± 39.7 (lux).

High-enrichment pens use less water (10.4 ± 0.4 L/pig/day) than low-enrichment pens (11.0 ± 0.4 L/pig/day). There is also an interaction between group size and enrichment (F1, 138 = 18.78, p <0.001; Figure 1). In the LARGE group, the high concentration group used less water than the low concentration group (p <0.001). Compared with the low-enrichment medium-sized fence, the high-enrichment medium-sized fence also found a trend of decreasing water consumption (p = 0.083).

The effect of group size and enrichment on water consumption (intake waste) L/pig/day (LSmeans ± SE). Group size: large (48 pigs/fence), medium (24 pigs/fence), small (12 pigs/fence), rich: low (wood hanging toy), high (wood hanging toy grass). The different letters of abc indicate significant differences found by the Tukey-Kramer test (p <0.05).

The hourly water consumption (intake plus waste) of each drinker was not affected by group size (F2, 26.7 = 1.17, p = 0.326) or enrichment (F1, 246 = 2.32, p = 0.129; Table 2). The hourly water intake (water consumption minus waste) of each drinker was not affected by group size (F2, 26.7 = 0.76, p = 0.477) or enrichment (F1, 246 = 0.99, p = 0.320). Compared with high concentration (F1, 61.6 = 9.82, p = 0.003), in low concentration fences, each drinker wastes more water per hour, and compared with large fences, medium fences have more water Waste trend (F2, 23.2 = 3.23, p = 0.077). The percentage of wasted water is not affected by the group size (F2, 27.3 = 0.68, p = 0.513), but compared with the high-enrichment fence, the low-enrichment fence wastes more water (F1, 74.7 = 6.46, p = 0.013). No interaction between population size and enrichment was found.

The 24-hour water consumption data collected from the water meters in each fence during the entire experiment was divided into six 4-hour blocks (recording interval of 15 minutes). The water consumption (L/pig/day) for each block and each treatment is shown in (Figure 2). The day and night patterns of all treatments were similar, with the water consumption of the drinking fountain increasing from about 8 am to 4 pm, and then began to decrease.

Six types of population size and enrichment (water consumption/pigs/day (L)) combined day and night drinking patterns that occurred in a 4-hour block.

Pigs of different herd sizes have similar drinking times, but compared with high concentration (15.5 times/drinker/hour, F1, 18.6 = 5.08), pigs with low concentration (24.4 times/drinker/hour) have more drinking times. High, p = 0.037) (Figure 3a,b). However, as the group size increased (F2, 11.9 = 3.07, p = 0.084), the round duration tended to shorten, and enrichment had no effect on the round duration (Figure 3c, d). The total check-in time per hour is not affected by the group size, but there is a concentration effect (F1, 18.6 = 5.08, p = 0.048). Compared with high-enrichment pigs, pigs in low-enrichment pens spend more time occupying the drinker (p <0.05) (Figure 3e, f).

The effect of population size and enrichment on drinking behavior (LSmeans ± SE) (a, b) Number of episodes per drinker (c, d) Duration of each episode (e, f) Per hour per drinker Occupied. Group size: large (48 pigs/fence), medium (24 pigs/fence), small (12 pigs/fence), enrichment: low (wood hanging toy), high (wood hanging toy grass) abc different letters Represents the difference found by the important Tukey-Kramer test (p <0.05).

The effects of group size and enrichment on pig behavior are listed in Table 3. Group size (F2, 8.34 = 16.69, p = 0.001) and enrichment (F1, 30.9 = 9.28, p = 0.005) have an effect on the aggressive behavior of pigs. The pigs in the MEDIUM (p = 0.007) and LARGE (p = 0.001) groups showed less aggressive behavior than the pigs in the group. Pigs with low enrichment showed more aggressive behavior than pigs with high enrichment (p = 0.0047).

High-enrichment fences exhibited fewer harmful behaviors than low-enrichment fences (Table 3), but due to the interaction between population size and enrichment (F2, 46.3 = 5.62, p = 0.007), caution must be exercised Explain the data. In the small group, pigs with low concentration showed more harmful behaviors than pigs with high concentration (p <0.001). Although in the LARGE group, there were more harmful behaviors in low-enrichment pigs, the difference was not significant (p = 0.15). Regardless of whether the enrichment level is low or high, the number performed in the MEDIUM group is numerically the same.

Compared with pigs in the MEDIUM and SMALL groups, pigs in the LARGE group had fewer interactions with enrichment (p = 0.05), and usually had more interactions with enrichment in the HIGH enrichment treatment (F1, 59.8 = 21.8 , P <0.001). Only population size and enrichment have a trend of interaction (F2, 59.8 = 2.76, p = 0.071), small and medium population sizes provide more interactions between high enrichment than large enrichment and enrichment.

Table 4 summarizes the impact of population size and enrichment on animal performance. Group size has an effect on ADG (F2, 18 = 4.46, p = 0.027), and ADG of LARGE group is lower than SMALL (p = 0.021). ADFI is also affected by the group size (F2, 6.52 = 4.77, p = 0.053), and the ADFI of the same large group is lower than that of the small group (p = 0.047). The level of enrichment or the interaction between population size and enrichment has no effect on ADG or ADFI. Group size or the interaction between group size and enrichment has no effect on FCR. However, pigs treated with low enrichment tend to have lower FCR (p = 0.065).

We assume that a larger group size and the provision of beneficial concentrated materials will optimize water consumption by reducing waste. The results show that the size of the group does not affect the water consumption of each pig. However, our hypothesis about providing enrichment has been confirmed; the high-enrichment pens use less water per pig than the low-enrichment pens, possibly because less water is wasted in this treatment. Providing high enrichment in a larger group is associated with reduced performance of aggressive and destructive behaviors, indicating better welfare. Although the size of the pen and the size of the group are confused in the current study, it may be mainly due to the influence of having a larger pen and more shared space, which drives the observed effect.

Water consumption includes water ingested by animals and wasted water. No treatment affects water consumption from 0930 to 1600 hours, an average of 7.81 liters/drinker/hour. Approximately 89.1% of the total water consumption was ingested (6.95 liters/drinker/hour) and 10.9% (0.85 liters/drinker/hour) was wasted. Compared with other studies, the water intake per pig is higher and the waste rate per pig is lower (70% intake, 30% waste11,> 30% waste/pig/day)12. Drinker design, height and flow rate have a great influence on these two parameters7 and can explain the difference. The design of the drinker in the current study means that the undrinked water of the pig is collected in a bowl located under the nipple, which may cause less spillage, and the water will be drunk by the pig, which means less manipulation of the pig nipple. In addition, in our research, pigs can also drink from the nipple present in the wet/dry feeder, which may affect the total water consumption and waste, because the overflowing water from these drinkers will leak into the feeder, It will be consumed with the feed so it will not be wasted. It should also be noted that we have some missing values ​​for water waste, which are excluded from the calculation, which may further affect the results.

In our research, the day and night patterns of water use within 24 hours are consistent with previous work. We found that water consumption was the largest during the day, peaking at 1600 hours, and decreased in the evening and night. This is similar to the pattern observed by other researchers8,20 and reported that the longest time spent with a drinker is between 1800 and 1900 hours8. This pattern also seems to follow the typical diurnal feeding pattern of pigs20.

Our results show that drinking time and the number of visits to drinkers are not affected by group size, which is similar to the results of other researchers12. However, these results are somewhat contradictory to the results of other researchers. They found that compared with the group of 60 pigs, the pigs in a group of 20 drinkers are more frequent, last longer, and drink longer; however, the results of these studies The ratio of pigs to drinking water is different (10:1 vs. 20:1), which may affect the results8,13. We do acknowledge that our detailed observations of drinking behavior were only conducted once during the experiment, and the use patterns of drinkers may be different in the early or late stages of completion. Nonetheless, our analysis of the occupancy rate of drinkers is consistent with the water and waste data collected over the past few weeks; pigs with low enrichment have more drinking times, the occupancy rate of drinkers is higher, and the percentage of water consumption and water consumption More water was wasted.

Therefore, our research provides new insights into the relationship between enrichment supply, water use, and drinking behavior. We provide grass as an additional enrichment in the HIGH treatment because it is very beneficial for pigs and even better than other attractive enrichment materials such as shredded paper and cork (eg spruce)15,16. It seems that part of the foraging motivation of pigs may have been satisfied after playing or eating grass. As a result, they may be less likely to interact with drinkers to meet foraging needs, nor are they likely to interact with them without drinking water. Another hypothesis is that eating grass may satisfy the thirst of pigs to a certain extent; the moisture content of fresh grass is approximately. 80!. Therefore, pigs may be less motivated to visit the waterer to drink, and therefore do not have time to sprinkle. If this is the case, our results may be somewhat specific to providing grass as an enrichment material; other enrichment strategies should be used for further research to determine whether the results are consistent between different materials. However, it is important to note that the proportion of water wasted in low-concentration pens is higher than in high-concentration pens. If the amount of wasted water has a linear relationship with the amount of water consumed, we expect the waste proportions of different treatments to be similar. The fact that the percentage of waste in the LOW treatment is higher indicates that these pigs sprinkle more water when interacting with the drinker than the pigs in the HIGH treatment.

Nevertheless, the difference in water use between enrichment treatments also varies with the size of the population. There was no enrichment effect in the MEDIUM and LARGE groups. In large enclosures, pigs have more shared space and therefore more areas to explore, which may reduce the number of redirected exploration behaviors for drinkers. In addition, the provision of grassland and shared space has an additional effect in reducing overall water use.

We found that pigs in the small group had a higher incidence of aggressive and harmful behaviors compared to the medium and large groups. Our results are not comparable to most studies on group size, because in the current study, all pigs have equal access to resources, which is not the case in most other studies. For example, a study investigating the effect of group size and rearing space changes (1:10 pigs and 1:20 pigs) on the welfare of finishing pigs found that as the group size increases, the number of skin lesions indicating aggression also increases by 22 . Compared with smaller herds (20 pigs), larger herds (80 pigs) tend to be less aggressive when mixed with unfamiliar herds23. The possibility of monopolizing resources decreases as the size of the team increases, and as the number of competitors increases as the size of the team increases, the number of people participating in costly struggles decreases by 24. Therefore, in larger groups, pigs seem to become less aggressive and may switch to low-aggressive social strategies25. The increase in solid floor area and the increase in space allowance are also associated with fewer tail damage behaviors and better overall welfare in fattening pigs26.

Although the effects of group size and fence size are mixed in the current study, we believe that it is prudent not to change the larger mixed effect of group size and stocking density, which would happen if we did not change the size of the fence . In addition, keeping the fence size the same means that the stocking density of smaller groups will be about 4 times lower than in a typical commercial system; therefore, although the results are theoretically interesting, they do not reflect commercial reality. We must also take into account that the stocking density of all treatments is slightly lower than the density required by EU law. However, the space allowance used is part of the research center’s standard operating procedures to minimize the risk of sabotage while maintaining some resemblance to commercial reality. We believe that the level of access to fencing resources (rich projects and keepers) may have a greater impact on the performance of these behaviors than the relatively small transfer of legal stocking density restrictions. Higher numbers of pigs per feeder may increase the risk of tail biting or attack, so that the results do not reflect the typical conditions of a well-managed business unit.

It has been suggested to provide sufficient substrate to stimulate foraging and exploratory behaviors to reduce destructive behavior in pigs27. From the current research, we have concluded that providing pigs with high nutrition can reduce aggressive and harmful behaviors. Our results are consistent with 28, which concluded that pigs in rich environments (peat and straw) spend more time exploring the substrate than pigs in barren environments. In this study, pigs spent more time in barren environments on harmful behaviors, such as nose and biting, and aggressive behaviors, such as heading. In addition, a recent study showed that compared with pigs with higher enrichment replacement rates, pigs with low enrichment replacement rates (that is, the enrichment materials are only replaced once every two days after they are exhausted) also perform better. Offensive and destructive behavior 16. Therefore, in our research, the continued existence of fresh grass as a substrate for exploration and consumption may help reduce aggressive and harmful behaviors. However, it should be noted that our behavior observations do seem to be a very short period of time, and the risk of certain behaviors may be relatively low. This is indeed the reason we classify the observed behaviors into the "aggressive" category. reason. ', harmful' and'enriched'.

In our study, despite the similar feed conversion rate, pigs in the large group had lower feed intake and lower weight gain compared with pigs in the small group. This may be because large groups of pigs, usually the dominant pigs, control the feeder entry22. Other studies have also reported that as the group size increases, the diurnal variation of feeder visits and hourly consumption of feed decreases. However, if feed resources and space allow sufficient, productivity is not affected by the size of the group30. In addition, in the current study, there are differences in the use of feeders, which may be caused by the fence design and the location of the feeders within the fence. Pigs in large pens prefer certain feeders. Since all feeders are used differently, it may affect the voluntary feeding behavior of pigs, thereby affecting overall feed intake and weight gain.

In this study, we found that herd size has no effect on water consumption or waste, but compared with low-concentration pigs, high-concentration pigs have lower water consumption and waste. Aggressive and harmful behaviors are only lower in large groups and in fences with high enrichment, not in all group sizes. Compared with the small group, the pigs in the large group had lower feed intake and daily gain, while the pigs/feeder ratios in all pens were the same. Therefore, we concluded that providing nutrition to pigs in the form of fresh grass next to wood and hanging toys can reduce water and waste, and have a beneficial impact on welfare.

The data set generated and/or analyzed during the current research period can be obtained from the corresponding author upon reasonable request.

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The author would like to thank Tomas Ryan, David Clarke, university interns Ana Isabel Valle, Gabin Gil and Richard Faivre-Picon, and the farm staff of Teagasc Pig Research Institute for their continuous help during this study. We would especially like to thank Shane Kenny for helping with all measurements during the study. The project was funded by Teagasc Walsh Fellowship (Grant No. 2017147) and Teagasc internal funding (project code 0182).

Pig Development Department, Animal and Grassland Research and Innovation Center, Teagasc, Moorepark, Co. Cork, P61 C996, Ireland

Shilpi Misra, Amy J. Quinn, and Keelin O'Driscoll

Wageningen University and Research Animal Production System Group, P.O. Box 338, 6700 AH, Wageningen

Shilpi Misra & Eddie AM Bokkers

Ministry of Livestock Systems, Animal and Grassland Research Innovation Center, Teagasc, Moorepark, Co. Cork, P61 C996, Ireland

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SM, KOD, EAMB, AQ and JU-planning experiments, SM-performing experiments, SM and KOD-statistical analysis of data, SM, KOD, EAMB and JU-data interpretation, SM-drafting manuscripts, all authors review manuscript.

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Misra, S., Bokkers, EAM, Upton, J. etc. The impact of environmental enrichment and group size on water and waste for growing-finishing pigs. Scientific Representative 11, 16380 (2021). https://doi.org/10.1038/s41598-021-95880-0

DOI: https://doi.org/10.1038/s41598-021-95880-0

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