How much floor space does a pregnant sow need in a group-housing system with electronic sow feeders?
Yuzhi Li, Alternative Swine Production
Determining floor space allowance for gestating sows can be controversial because more floor space allowance means low output per square footage of the barn and will potentially reduce profitability for producers. On the other hand, floor space allowance less than sow requirement can compromise sow welfare and performance. To answer the question in the title of this article, we conducted a two-year project (titled ‘Determining the Minimal Floor Space Allowance for Gestating Sows Kept in Pens with Electronic Sow Feeders’). The project was partially sponsored by the National Pork Board, and the research team includes Yuzhi Li and Lee Johnston from the WCROC in Morris, and Sam Baidoo from the SCROC (Southern Research and Outreach Center) in Waseca.
We used 928 sows to evaluate four levels of floor space allowance: 22 ft2, 20 ft2, 18 ft2 and 16 ft2 per sow.
The 22 ft2 allowance is considered a high standard and recommended by the European Commission Council. The 16 ft2 allowance is equivalent to the floor space allowance for housing the same number of sows in pens as in gestation stalls, which is usually considered less than requirement of the sow. To test whether providing more space during the initial mixing period will improve welfare and performance of sows with limited floor space (16 ft2), we imposed the fifth treatment which was to give sows more space (22 ft2) during the first week when mixing into pens, and allowed them 16 ft2 for the remaining gestation period.
Each floor space allowance was tested in four pens (42 to 51 sows per pen) over a period of 18 months. Sows were moved to pens with an electronic sow feeder (ESF) after being tested pregnant at 5 weeks after mating. Sows remained in their pens until day 109 of gestation and moved to individual farrowing stalls. Sows weaned their piglets at about 18 days after farrowing. Sows that were rebred within one week after weaning a litter were considered to have completed the study.
Results indicate that floor space treatments did not affect performance, skin lesions, stress hormones, fighting or postural behaviors of sows. In other words, increasing floor space allowance from 16 ft2 to 22 ft2 did not add benefit to welfare or performance of sows. These results suggest that the space allowance of 16 ft2 is acceptable as the minimal space allowance under conditions of the current study.
When looking at our results closely, we feel that sows used in the current study may need less floor space compared to sows housed and managed in other systems for several reasons. First of all, all sows used in the current study had been group-housed in the ESF system since they entered the breeding herd as gilts, and managed as static groups. As a result, 50% to 70% of sows in a pen were housed as pen-mates during their previous gestation, and became familiar to each other. Familiar sows fight much less compared to unfamiliar sows at mixing in pens, resulting in less injuries to sows in all treatment groups. So, familiar sows may need less floor space than unfamiliar sows. Secondly, in the current study, all sows had been allowed 16 ft2 floor space in the ESF systems before the study started. These sows probably had adapted to the minimal floor space allowance of 16 ft2. Thirdly, sows in the current study appear to be lighter than sows in previous studies. Lighter weight is associated with smaller body size which may contribute to less space requirement. Finally, sows moved into ESF pens after sows were pregnant. Pregnant sows are less aggressive compared to sows that are just mated or weaned. Again, sows that are less aggressive may need less floor space.
As a result, the minimal floor space requirement obtained from this study might be lower than requirement of sows in other group-housing systems. When applying results of this study, producers should consider affecting factors, such as housing and feeding systems used, management protocols adopted, and genetics and experience of sows.