In the management of group housed sows, keeping sows in stalls from weaning until five weeks after breeding is a common strategy that serves to prevent aggression, control individual feed intake and facilitate management during breeding. However, pressure to reduce stall use continues, and alternative management options should be explored to determine what other viable options are available to producers. This study compared the effects of three mixing strategies on sow performance in fully-slatted group pens, with sows fed daily in free-access stalls. A total of 252 sows were studied over six replicates, in groups of 14 sows/pen (2.2 m2/sow). The treatments consisted of: i) Early mixing (EM) – sows mixed into groups at weaning; ii) Late mixing (LM)- sows stall-housed at weaning and mixed at five weeks gestation; and iii) Pre-socialization (PS)- sows mixed for two days after weaning, then stall housed for breeding and up to five weeks gestation, after which they were mixed (same groups). The PS treatment provided an intermediate treatment to examine the interaction between mixing at critical time points in combination with housing sows in stalls during the implantation period. The PS treatment also allowed us to study whether aggression at remixing can be reduced if sows have previously established their social order. For consistency, all treatment groups were housed in free-access stall pens in one gestation room. The free-access stalls were used to house sows during feeding, and for heat checks and breeding. Sows were fed each morning in free-access stalls, after which they were locked out of the stalls, ensuring that sows spent up to 22 hours per day in the loafing area. It was of interest to determine whether measures of aggression, sow welfare and sow reproductive performance (wean-to-service interval, conception rate, and farrowing performance) differed among treatments. Estrus behavior was measured on days 3 and 4 after weaning in the EM group only, to determine if keeping sows loose from weaning can help to stimulate group estrus behavior.

Results indicate that the EM treatment had the highest conception rate (98%), followed by the PS treatment (94%) with the LM treatment having the lowest conception rate (87%). This may reflect sub-optimal stimulation of estrus in stall housing (LM). In comparison, the EM and PS groups received mixing stress immediately at weaning, which may have stimulated follicular growth and clearer estrus expression. The EM treatment also showed a significant reduction in the number of stillborn piglets, which may be an effect of improved sow fitness and/or activity levels during early gestation. There were no other differences in production performance among the treatments. There was no difference in the amount of aggressive behavior performed at mixing, not even when comparing the second mixing of the PS treatment to the first mixing of EM and LM. Between the treatments, there were no significant differences in cortisol levels or sow lameness. Injury scores were lower in PS sows compared to EM and LM sows after the first mixing. When remixed, sows in the PS treatment had significant increase in injuries than following the first mixing. However, injury scores on all sows were very low. Overall, this suggests that sow welfare was not significantly affected by any of the mixing treatments.

It can be concluded that under good conditions of management, where sows are housed in static groups and individually fed, mixing sows at weaning does not negatively impact sow performance or welfare. Furthermore, there may be production advantages to be gained from mixing sows into groups at weaning, as evidenced by improved conception rates and reduced stillborns, and these effects should be explored further. For the PS treatment, although production levels were acceptable, the mixing of sows twice did not result in reduced aggression and did not provide any obvious advantage.

Researcher contact information: Dr. Jennifer Brown, Prairie Swine Centre, PO Box 21057, 2105 8th Street E., Saskatoon, SK, Canada, S7H 5N9, Tel: 306 667-7442"", Email: [email protected]