If herding cats is the ultimate challenge, managing sows is a close second. This is especially true with the advent of group housing and its unique dynamics. In such systems, proper management is key to minimizing stress for sows, thereby boosting sow reproductive performance and piglet development. Given the stakes for producers, scientists are working hard to find the best approach.

In exploring the pros and cons of different group management systems, Canadian researchers focused on dynamic versus static grouping and compared early and late mixing of sows. With the dynamic mixing approach, multiple breeding groups are housed together in each pen. As small groups of sows are moved out to be farrowed, new groups of recently mated sows join the pen.

In static groups, each pen houses only one breeding group of sows. The animals are only mixed at the start of gestation, and no sows can be brought in for replacement if a sow is removed. The choice to implement dynamic or static housing can have big impacts for barn design.

Mix and mingle

Dynamic mixing is a popular choice for producers, allowing use of new technology and providing individual feeding for sows. But researchers are concerned that there is potential for more conflict, aggression and stress as groups of sows move in and out of the pen. When it comes to sows, there is “mixing aggression” and “ongoing aggression”. Researchers were concerned that ongoing aggression in dynamic groups would be a problem. What they found was that mixing aggression, which happens only once at the beginning of gestation, was reduced in dynamic groups because there were fewer new group members. At the same time, they found that ongoing aggression resulted in more lesions in dynamic groups throughout gestation, but it was not enough to impact their production. This suggests that mixing aggression is more important than ongoing aggression in terms of the impact on reproduction.

Late mixing (after 28 days of gestation) is also largely favoured over early mixing, but this may not be sustainable given the concern shown by consumers. As pressure grows from the public to abolish month-long stays in gestation stalls, researchers are examining early mixing more closely as a viable option.

Interestingly, this study found less aggression in dynamic systems over static ones (both mixed early). In the former, aggression levels were low when each small group was added, compared to one large mixing event for the static housed sows, which occurred in early pregnancy.  The production results were also surprising: Dynamic sows had the highest farrowing rate over static sows, and even over a control group of late mixed sows.  There is not a clear winner between static and dynamic; both systems are popular and will continue to be so. They require very different approaches, so industry must be more aware of those differences to fine tune management strategies.

Social status is important, because if a system is not running well, it is always the subordinate sows who get the short end of the stick, and it is usually the younger/smaller animals that are subordinate.

With genetics, the swine industry needs to shift the genetic focus away from producing more piglets and onto finding less aggressive sows that are well built and robust to function well in group housing.

Climbing the Social Ladder

Another important factor influencing a sow’s reproductive performance was social status within the pen. Researchers determined each sow’s rank within the group as dominant, intermediate or subordinate based on a feed competition test. A sow’s rank played a large role in setting their stress level, which in turn affected piglet behavior and physiology. The exact connection is not yet clear, but scientists hope to learn more as they review the data.

As part of the project, researchers also examined sow mortality in the wake of growing death losses on farm. Using a survey and follow up visits that covered 104 herds, they found higher mortality in large herds (3,000 or more) versus small, and in group gestation versus stalls. Scientists were especially concerned that the majority of death losses in group gestation involved younger sows. Apart from the animal welfare implications, early culling is an economic blow for the business. Most producers can attest that sows who manage fewer than three parities don’t even cover their replacement cost.

Finding genes that fit

These mortality findings are critical for industry going forward. The increase in lameness should spawn a greater focus on all aspects of gilt development, and genetics companies could prioritize conformation (functional legs and feet) and a calmer temperament that is less prone to aggression. Greater robustness traits would be beneficial as well, making sows more durable in group systems as they navigate concrete floors and interact with their pen mates.

Addressing the mortality issue will take a combined effort from researchers and producers. It is vital that worker training and compliance on farm be more consistent, and that staff use the same definitions between farms and within the same operation. What constitutes “culled”, “euthanized” and “died on farm”? For their part, the project team plans to have recommendations for workers soon on what to record.   

Aiding in this study was Dr. Yolande Seddon, assistant professor, Department of Large Animal Clinical Sciences at the Western College of Veterinary Medicine. At the same time, Dr. Nicolas Devillers, research scientist in pig behaviour and welfare at Agriculture and Agri-Food Canada (AAFC), advised the team on dynamic mixing. Also of note, Dr. Brian Sullivan, CEO at the Canadian Centre for Swine Improvement (CCSI), worked closely with the group on sow mortality.

For the pork sector, the only constant is change, and the move to group sow housing is a prime example. The more producers can learn today about managing group gestation and limiting sow mortality, the better equipped they’ll be to face the future.