There is also an increased interest from consumers in "humane-raised" pork. Together this means that Ontario producers may want to investigate the possibility of switching from crated gestation to group sow housing.

Sows naturally establish a h ierarchy when kept in groups. Establishing this hierarchy involves a certain number of aggressive encounters for one to three days after sows are mixed together. Good pen design, feeding techniques, and management will decrease the frequency and intensity of these aggressive encounters.

The techniques listed below are used successfully by producers in Ontario who use pen gestation for their sows. Since group sow housing systems vary dramatically, producers may need to modify or use a combination of these suggestions to limit aggressive encounters between sows. The suggestions below are listed in order from least to greatest difficulty (based on labour and cost) to implement.

1. Wean sows into breeding crates

This is only difficult to achieve if your converted facility does not have enough crates for one week’s weaned sows. Producers using group sow housing hold weaned sows in breeding crates for various times, but very few wean directly into pens. During estrous, sows will ride each other and can injure themselves and others in the process. Weaning into breeding crates prevents this. Many producers wait until the 28 day pregnancy confirmation ultrasound before mixing a group of sows. Others have success mixing after seven days in the crates, i.e. directly after breeding. Since implantation occurs around 12-14 days post breeding, it is best to group the sows before or after this time.

2. Put extra feed on the floor of the pen before a group of sows enters.

This is a distraction technique. A similar technique is to put a bag of shavings on the floor of the pen. The sows are too busy eating (or investigating in the case of shavings) to bother fighting with each other. Some producer s feed extra feed (1.5 times the normal ration) for two to three days after a new group is mixed.

3. Add a boar to the pen

The boar assumes the role of "leader" and keeps aggressive encounters between sows to a minimum. If the boar is too aggressive he may injure a sow. If he is not aggressive enough, a dominant sow may attack him, so you need a boar with the correct temperament for this work.

4. Mix the new group at the end of the day and turn out the lights

Many producers combine this technique with adding extra feed on the floor. The theory is that the sows are calmer when they are full and the barn is quiet and dark.

5. Mix groups of sows by size

Try to prevent groups from having one or two very small or very large sows as these "outlier" sows can often be quite dominant or submissive. This is notwithstanding that some small sows (particularly gilts) can be very aggressive sometimes.

6. Larger groups of sows (20 or more)

Larger groups of sows seem to reduce the number of aggressive encounters. Aggressive sows don't bother to pursue a sow through a larger group and the sow being chased can hide within the larger group. Smaller groups of sows (generally less than 10) are more prone to the establishment of strict dominant hierarchies than larger groups of sows. It appears that groups can be so large that sows "give up" trying to establish a hierarchy.

7. Add partition walls

The addition of partition walls (either cement or hanging rubber mats ) provides sows with hiding places when being pursued by an aggressor. Often if the sow can get out of sight, the attacking sow stops the chase.

N.B. If you have converted partially slatted grower-finisher pens into housing for gestating sows, it is possible to combine #5 and #6 by opening the partition at the back of the pen (over the slats) that separates two pens. In this manner sows are able to choose which side of the pen and which sows they prefer to congregate with. The solid pen divider over the solid area now serves as a visual barrier. By thus combining two pens one also gets the benefit of increased sow numbers. This may increase the work load for staff prefarrowing, if they need to sort sows that need to go to the farrowing room. Batch farrowing can sometimes overcome this problem.

8. Spread out the feed

Aggressive encounters between sows occur most often during feeding. By spreading the feed over the entire solid floor surface, there will be more distance between the sows as they are eating. This decreases aggressive sow encounters. The addition of an inverted "Y" PVC pipe or a cone underneath the drop feeder is an inexpensive way to spread out feed as it drops. A second but more costly method is to add a second row of drop feeders, set apart from the first.

N.B Having two or more separate solid s urface areas for feeding (ie separated by partition walls or a centre dunging area) is the best way to reduce aggression when feed drops.

Submissive sows then have the ability to move away from dominant sows to a different area to eat.

9. Feed the sows multiple times a day

Sows are often fed once a day. This results in a large amount of anxiety just prior to and during feeding and causes more aggressive sows to hoard feed increasing fighting between sows. Feeding smaller amounts three to eight times throughout the day, results in calmer sows during feeding as they are not as frantically hungry prior to being fed.

Create one or two "ideal" sow mixing pens.

**This idea has not been tested in Ontario (that I have seen). If producers are renovating a conventional crated barn to group housing, they may not have the space or the extra money to invest in having all the group sow gestation pens being the "ideal" model (eg partition walls, separate feeding areas, multiple rows of feed drops). One idea would be to have a few "ideal" mixing pens. After their time in the breeding crates, a new group of sows would be mixed and held in these pens for one week. The same group would then be moved to a more traditional group pen for the rest of their gestation. However, since this idea has not been tested, it is possible that the intensity and frequency of aggressive encounters may again increase once the sows are moved into the second, more traditional pen.

The work that resulted in suggestions 1 through 9 was performed on Ontario farms with group sow gestation housing. Swine producers tested these methods, through trial and error, and came up with solutions that resulted in limited aggression between sows, when mixed after breeding. These techniques were considered successful for several reasons: the sows have fewer scratches, injuries, and lamenesses and their body condition remains very even. The farrowing rates are greater than 80 per cent and producers rarely pull a sow out of a pen that is not doing well in the group situation. Finally, producers find working in group sow housing barns a quiet and pleasant alternative to crated gestation.

November 2007