Reproductive traits of sows penned individually or in groups until 35 days after breeding.

We compared estrous and farrowing traits in 274 Duroc X Yorkshire sows penned either in individual gestation stalls or in groups (four or five sows/group) during the intervals from weaning to breeding and from breeding to 30 to 35 d after breeding. Sows were assigned to treatment by parity (primiparous vs multiparous), checked twice daily for estrus from 3 to 10 d after weaning and artificially inseminated (AI) twice during estrus. Ovaries of anestrous sows were examined at laparotomy. No major treatment effects on estrous response were detected and 88% (45/51) of anestrous sows had only small ovarian follicles. Litter traits were not affected by penning treatments. However, penning sows in groups postbreeding resulted in a 50% reduction (P less than .05) in early pregnancy losses as indicated by low serum progesterone 19 to 23 d after AI or return to estrus by 23 d after AI. This resulted in a 12 percentage point higher (P less than .05) farrowing rate for group-penned (78%) than for individually penned sows (66%).