Today, most pregnant sows in the United States are housed in individual stalls. However, public sentiment has been pushing the industry to move away from individual housing and toward group housing. Recent announcements by Smithfield Foods and Maple Leaf Foods that they will shift from individual gestation stalls to group pens in the next 10 years will likely trigger other production groups to make that transition, as well.
The aim of gestation housing should be to:
Ensure a suitable environment for sows.
Keep sows protected from other sows.
Feed sows at levels to achieve acceptable body condition at farrowing.
Maintain pregnancy, health and well-being of the sows.
Provide a safe workplace for animal caretakers.
Ensure that the system is robust to errors in management.
Meet these priorities economically.
So, which system works best, individual stalls or group pens?
The answer is “it depends.” There are many different sow gestation options, and many ways to evaluate whether one system is better than another. Evaluations can be based on performance, animal behavior, physiological responses or other criteria.
Considering the options
The individual gestation stall is a system that is fairly universal in type and management. In other words, there are few options. Sows can be fed manually, but automatic feeding is more common. Typical stalls are 2 feet wide by 7 feet long, although some larger stalls are now coming onto the market.
However, there are many options and differences in group-sow-housing systems. They can apply different feeding systems, such as dump or trickle feeding, use of feeding stalls or electronic-sow-feeding stations.
Dump or trickle feeding involves dispensing feed on the floor; it allows sows to eat simultaneously. It provides a simple, relatively inexpensive option to feed sows and can be used for large or small groups. It does not allow for individual sow feeding. Because sows are not protected from one another during feeding time, large “bully “ sows will consume feed disproportionately compared to small, more timid sows in need of a higher plane of nutrition.
Providing feeding stalls within group-housing pens provides the opportunity to feed sows individually and protect them from fighting during mealtime. However, good observation skills are required to adjust feed levels for each individual sow, on the go. Additionally, some people may not perceive this system as welfare friendly since it involves individually crating sows for short periods.
A third option is electronic-sow-feeding stations or ESF. This allows accurate individual sow feeding. It also can accommodate easy and quick identification of sick or off-feed sows. The sows housed in a group are tagged individually with ear-tag transponders and have access to an electronic feed station. Only one sow is allowed to consume feed at a time, and when the sow’s daily feed allotment has been distributed, no more feed is dispensed. Sows are not fed at one time, so aggression and fighting can occur while sows wait to enter the feeder. This system does require a much greater level of management, especially when it comes to training gilts and sows to use the system. Also, a backup plan is needed in case the feeding system should fail.
And the research says . . .
So how do individual and group-housing systems affect actual sow welfare and production? The University of Minnesota sow research unit at the Southern Research and Outreach Center in Waseca, Minn., has collected data for nearly five years, attempting to answer many of the questions surrounding gestation-sow-housing systems. University of Minnesota researchers Sam Baidoo, Robert Morrison, R. D. Walker, John Deen and L. Anil have conducted numerous trials evaluating sow behavior, health, welfare and performance, in individual and group-housing systems.
The 800-sow unit contains individual gestation-sow stalls (2 feet by 7 feet) and large, 50- to 60-sow group pens (22 feet by 42 feet) with ESF stations. All sows are placed on fully slatted, concrete floors. The sow herd consists of GAP genetics (Genetically Advanced Pork, Winnipeg, Manitoba), and sows are maintained throughout their reproductive lives in one of the two systems.
The frequency of injuries, stress-hormone levels and aggression levels are higher in ESF, group-housed sows compared to stall-housed sows (see graph). Most of the aggression in the ESF system is related to mixing sows and feeder entry. Because the ESF system allows only one sow to eat at a time, others wait in front of the feeder for their turn. This competition causes aggression among sows, which was found to be proportional to waiting time. Bite injuries to the vulva and legs are most common for this system, as are more substantial injuries to the legs and feet, causing reduced ability to walk comfortably. Feet and leg injuries are much higher than for sows housed in group pens on concrete, as well as for stall-housed sows.
Stall-housed sows tend to have higher injury scores and stress-hormone levels in late gestation compared to mid-gestation. Total injury scores for sows in stalls have been found to increase as body weight increases. This suggests that movement restriction due to limited space in stalls is much less significant during early and mid-gestation, and causes more problems in late gestation. It may also indicate that stalls currently in use are not large enough to appropriately handle late-parity and large-framed sows.
Performance and longevity
Housing type has little or no significant effect on sow weight and backfat changes during lactation. However, ESF, group-housed sows moving into farrowing crates tend to be in more ideal body condition than sows housed in stalls. This may be more a response to the feeding system, since within the ESF system it’s easier to adjust feeding rates versus manually adjusting feeder drops for stall-housed sows.
Actual differences in production performance, however, including conception rate, litter size, pigs born alive per litter and stillborns per litter, have not differed between housing groups. It’s worth noting that group-housed sows appear to be more restless during parturition and early lactation, which has resulted in greater pre-weaning mortality.
Sow longevity also has been an issue with sows in group pens. Although sows in individual gestation stalls exhibit more shoulder lesions and abrasions, sows housed in pens with ESF systems are removed or culled more frequently, the major reason being lameness.
So, what’s the answer?
No question, the gestation-stall versus group-pen debate has been turned up a notch, with Smithfield’s and Maple Leaf’s announcements.
Observations from our research at the University of Minnesota would suggest no clear-cut advantage to either group or stall housing. Gestation stalls have been designed to provide sows with protection from other aggressive sows. Movement restrictions, especially in late gestation, can increase injuries and may suggest a need for larger space allowances and crates for some sows.
Large-group pens equipped with electronic-sow-feeding stations provide additional room for sows to roam and interact with each other, but also greatly increase stress level, aggression and injuries, especially when sows are initially mixed together. It’s likely that modifications to the way group pens are designed and managed will be necessary to make them more effective in today’s modern production systems.