Unlike stall housing where the management options are fairly limited, there are many ways to manage sows in groups. Consequently, good feeder, pen and management choices are essential to success in group gestation.
Differences in group housing systems are based primarily on the feeding system used. However, there are also important interactions between the feeding system and mixing practices, pen layout, flooring and group size that can influence sow health and productivity. This article outlines some of the key principles to consider when managing sows in group systems.
The feeding system used has a significant effect on the availability of sows’ key resource: food. Feeding systems can be categorized as either competitive or noncompetitive, depending on how feed is presented. In competitive feeding systems, feed is provided in a common area, typically on a solid-floor area or in short stalls, with all sows having access to feed at once. In competitive feeding, sows can gain access to more feed through aggression or winning a fight. These systems are managed with smaller groups (from five to 30 sows per group) and require more hands-on management, including careful selection of uniform groups and daily checks on sows during feeding to monitor health and body condition.
In noncompetitive feeding systems, sows are isolated and fed individually, so opportunities to gain more feed through aggression are limited. Electronic sow feeding systems and free-access stalls are the most common noncompetitive systems. Their main advantage lies in reducing feeding aggression and allowing greater control over individual feed intake.
However, although ESFs do allow individual feeding, there can still be competition for access to the feeder. Controlling competition by not overstocking feeders and by designing pens and feeders to reduce multiple feeder entries is important for the success of these systems.
Training of new sows and gilts is an important aspect of ESF systems. Animals must enter the feeder to access feed, and so they must first learn how the entrance gate works. Entrance gates vary in design and function, depending on the manufacturer, and gilts, in particular, can be fearful and reluctant to enter.
Most farms with ESF use a training pen area where new animals can become familiar with the system. An actual ESF can be used but is not required; the training pen can be as simple as using the entry/exit gates from the ESF separating feeding and drinking areas. When using an ESF feeder for training, pen gating is used to crowd animals near the entrance and allow daily sorting of animals that have fed from those that haven’t.
One of the greatest concerns with group housing is aggression among sows. Injuries sustained during fighting are a significant concern for producers, as severe injuries can result in the need to cull valuable animals from the herd. However, research on aggression in sows has found the majority of injuries sustained in group sow housing are superficial scratches around the neck and shoulders; less than 1% of the injuries observed are considered severe. Overall, sows in groups generally “get along,” and there are many management techniques to reduce the incidence and severity of aggression. To effectively reduce and manage sow aggression, it is important to understand what causes it in the first place.
Some aggression will naturally occur at group formation as sows establish their social status. Aggression at group formation can be intense, but it is short-lived, with most fights occurring during the first two hours after mixing. Fighting can also take place during daily feeding, especially in competitive feeding systems. Daily aggression over feed access is a more serious issue, causing chronic stress and potentially the removal of poor-doing sows from the group.
In the wild, groups of sows include related individuals and their offspring. Each group has its own territory and social order, and will drive away unfamiliar animals. When penned together on-farm, sows do not have the option to leave, and the animals will fight to establish their dominance within the group. The initial mixing aggression is short-lived and intense, typically involving the more dominant and unfamiliar animals. Afterward, social tolerance develops as sows communicate using more subtle “avoidance” behaviors. The tolerance of new group members develops gradually in a process lasting several weeks. Thus, newly introduced animals will often be seen lying away from the main group of sows, often in less preferred areas of the pen.
Techniques for reducing mixing aggression include grouping familiar sows (when possible), providing sufficient floor space per sow, and the use of pen dividers (partitions) to give sows divided space and hiding areas to escape aggression. Pen partitions are typically 7 feet in length and help to define lying areas as sows prefer to lie against a solid wall. While partitions are typically 4 feet high, studies completed in Denmark indicate that short walls (e.g. 2 feet) can also be effective. Short walls can improve air flow and make it easier to see sows in the pen, but care should be taken to ensure that they are not placed in areas where sows may jump over them, causing injury. Large, rectangular pens will also allow more room for sows to avoid one another and good flooring (e.g., partially slatted, gaps no greater than 0.8 inch) will reduce the likelihood of hoof and leg injuries.
Static and dynamic groups
Gestating sows can be managed in either static or dynamic groups. For static groups, all sows in a group are mixed on the same day and remain in that group for the rest of gestation, with no new animals added. Static groups are used in competitive feeding systems and in some noncompetitive systems.
In competitive feeding, groups should be formed of sows that are uniform in size, as this helps to even out competition. With only one mixing at group formation, static grouping allows sows to form a stable group hierarchy, helps to reduce competition and allows all sows to feed. In competitively fed pens, sows should be observed daily at feeding, and any that are injured or losing body condition should be removed promptly to comfort pens. No new sows can be added to small static groups, as any new animals will be targeted for aggression from other sows.
In dynamic groups, small groups of sows are added to a larger existing group periodically throughout gestation, and groups are also removed periodically as sows move to farrowing. Each time a new group is added a new bout of aggression will occur. However, with large, dynamic groups it has been shown that sows adopt a more tolerant and passive response to unfamiliar animals. A pen layout that includes adequate space, and the addition of dividing walls for escape and to hide behind, helps to reduce the aggression.
Group size can also influence sow aggression within the group. Smaller groups of sows (eight to 10) will form a social structure with stable, linear hierarchies. Larger groups of sows (40 or more animals) develop a different social structure in which there is a greater tolerance and less aggression. It is believed that the cost of establishing dominance in a larger group is greater, and so animals learn to adopt a more tolerant approach rather than trying to dominate. Instead, sows in large groups will form smaller subgroups, or cliques, of sows that lie together.
With dynamic grouping, maintaining large groups is one way to help control aggression. In the dynamic setting, the addition of a smaller group of sows to the larger group lends itself to the natural formation of subgroups of sows. To help reduce the stress to animals added to a dynamic group, it is recommended that animals added to a new group should make up at least 10% of the total group size.
Many producers use an introduction pen that allows incoming sows to be penned together and become familiar with one another before joining the larger group. These sows typically remain together as a sub-group once they join the larger group. A specially designed mixing pen can also offer better conditions to minimize aggression and stress, including features such as extra space per sow, better flooring to help prevent injuries and provision of enrichment or bedding.
Grouping by size
Grouping sows by size (and/or parity) can help to even out competition within the group, helping in particular the smaller, younger parity sows to do better by not having to compete against larger, older sows. Grouping by size is especially important in competitive feeding systems where smaller sows will be at a distinct disadvantage when competing for feed.
Research has also shown advantages to grouping sows by parity in noncompetitive feeding systems. Grouping sows by parity was found to be advantageous for parity 1 sows managed in a static ESF system. Younger sows in the study were able to maintain backfat when housed together, but lost backfat during gestation when kept in mixed parity groups. It is likely that maintaining the sows in uniform parity groupings reduces competition for entry to the ESF feeder, helping to ensure all sows receive their daily feed allowance.
Research indicates that grouping sows by parity can also benefit young sows fed in free-access stalls. When housed in mixed-parity groups, younger sows spent the majority of time in the free-access stalls, but when housed with other young animals, the sows spent more time out of stalls in the common loafing area.
Time of mixing
There are three acceptable times when sows can be introduced into a group for gestation: at weaning, post-insemination and after confirmation of pregnancy (28 days of gestation). Research and practical experience have shown that each of these can be made to work, and it is a matter of preference for the producer. Mixing after confirmation of pregnancy is a strategy to help ensure a successful pregnancy through maintaining individual management from weaning until the pregnancy is firmly established. Mixing at this stage ensures no effect on conception rates, but can influence farrowing rate. Initial research suggests there may be effects of mixing stress on the unborn piglets.
Mixing post-insemination avoids this, with the stress over before implantation takes place. Providing mixing is performed before day 9 post-insemination, there should be minimal influence on conception rate. Sows should not be mixed during the period of embryo implantation (days 11 to 18 post-breeding) because this can result in reduced embryo survival, or a failure to conceive entirely. Many producers operating groups fed by ESF prefer to mix sows post-insemination, allowing monitoring of feeding through early pregnancy with the ESF.
Returns can be checked for automatically through the position of a boar pen at the exit to the ESF feeder, with an RFID tag reader on the boar pen. Mixing sows immediately post-weaning also ensures the mixing stress is over prior to implantation. Previous concerns that mixing aggression may reduce the onset of estrus have proved seldom to be true, especially in well-managed group systems. Rather, mixing sows immediately after weaning may stimulate the onset and synchronization of heat. However, flooring must be of good quality to prevent sow injury through mounting behavior.
Regardless of the chosen time to mix, aggression appears to be similar for each option, and management strategies to minimize aggression should always be employed. Ensuring adequate feed intake for all sows from the point of weaning until confirmation of pregnancy is key to the reproductive success. For this reason, competitive feeding systems lend themselves to mixing sows after confirmation of pregnancy, while systems offering individual feed control provide more options for mixing post-weaning or insemination.
Quantity and quality of space
The key to success when managing sows in groups is to address sow comfort and to minimize competition for resources where possible. To manage sow competition, the design of pen layout is closely linked to the type of feeding system.
For example, in free-access stalls, a minimum distance of 10 feet is recommended between rows of stalls. This minimal alley width is needed to ensure sufficient space for sows to back out of stalls freely, and to facilitate sows walking past one another with minimal interference. Therefore, the total space provided to sows in free-access stalls needs to accommodate not only the feeding space provided to each sow in the stall, but also the loafing area behind stalls. Consequently, these systems require significantly more space. However, the added space and cost requirements are balanced out by the ease of management and flexibility offered by these systems.
With ESF systems, many sows share a common feeding stall, and the remaining pen space is available to be used for sleeping, dunging and exercise. However, as with the free-access stalls, a minimum alleyway width of 8 feet is recommended between lying areas to provide sufficient space for sows to walk past one another with minimal interference and to prevent one bully sow from effectively blocking the passage.
In Canada, space recommendations for sows kept on partially slatted floors are 15 to 18 square feet per sow for gilts, and 19 to 24 square feet for sows. However, as noted above, the space provided will depend on the pen design and feeding system used, as well as on parity and group size.
It is recommended that space allowances in small groups (10 sows or less) should be greater, and large groups (40 sows and over) can be managed with somewhat lower space allowances. In a competitive feeding system, it is wise to provide a space allowance in the upper limits of the recommendations per animal.
The quality of pen space is equally as important as the quantity of space. Pen features can help sows to properly designate feeding, drinking, lying and dunging areas, and can promote movement and pig flow within the pen. The movement of sows throughout the whole of the pen can be encouraged by proper ventilation and the strategic placement of resources throughout the pen. For example, providing water outside of feeding stalls will encourage sows to exit stalls to access water.
Increasing the complexity of the pen environment through the provision of solid dividing walls can provide escape areas for sows to retreat to and remove themselves from the main group. A dividing wall serves a dual purpose as a physical barrier, removing the sow from visual contact with other sows, and as an attractive lying area. Given a choice, sows will seek out a solid wall to lie up against. Therefore, placing solid walls throughout the pen will increase the amount of preferred lying space within the pen and help the formation of social subgroups of sows.
Quality of space can also be improved by increasing the comfort of the flooring. While slatted floors are preferred for ease of manure management, solid flooring provides improved sow comfort for lying. Therefore, partially slatted systems offer a balance of manure management and sow comfort. Typically, sloped solid flooring is provided in designated “bedroom” areas, and slatted flooring is used in alleys and dunging areas. Because solid flooring encourages lying in designated areas it helps in keeping the alleys clear, and promotes ease of movement within the pen.
Sow comfort can be further improved by providing bedding in solid areas (which also doubles as providing enrichment) or by using rubber mats. Where slatted flooring is used, good quality slats are of great importance to avoid injury (e.g., torn dew claws), and also increase sow comfort when walking. European Union requirements specify a slat width of 80 millimeters (3.2 inches) or more, and a gap width of 20 mm (0.8 inch) or less, and these allowances have been shown to work well.
For slatted systems, the provision of enrichment to provide an outlet for exploratory behavior by sows is a worthy addition to encourage sow movement throughout the pen and help promote behavioral calm. Increased sow exercise leads to increased sow fitness, which has been found to positively link to improved bone strength, muscle mass and ease of farrowing.
While the management of group-housed sows is more complex than managing sows in stalls, there is the potential for improvements in sow health and, as a result, productivity. Success with group housing is more dependent on the design and management of each system, including good stockmanship and observational skills.
With the proper combination of feeding management, pen design and grouping practices, group-housed herds are regularly achieving production levels of 30 pigs per sow per year and greater. The physical condition of sows is improved by allowing greater activity, and with consideration for proper space allowances, pen features and flooring, levels of aggression and injury can be kept to a minimum.