ENDOCRINE CHANGES DURING GROUP HOUSING OF PRIMIPAROUS SOWS IN EARLY-PREGNANCY

The effect of group housing sows during early pregnancy on maternal en docrine changes and on embryonic survival was studied. Twenty crossbre d (Swedish YorkshirexSwedish Landrace) primiparous sows were used. On day 11 +/- 1 of pregnancy 3 unacquainted sows were randomly assigned t o a single pen measuring 3mx3m in area. A fourth sow in each group was housed in an individual pen and used as a control. This procedure was repeated 5 times to collect data from 5 animals in each rank as well as in a control group. Blood samples were collected from the day befor e grouping to day 5 after grouping for cortisol, corticosteroid-bindin g globulin (CBG), progesterone (P-4), oestradiol-17 beta (E(2)) and pr ostaglandin F-2 alpha metabolite (PG-metabolite) analysis. A rank-orde r test and an ACTH test were performed on day 4 and day 5 of grouping respectively. The sows were slaughtered on day 17 +/- 1 of pregnancy a nd embryos recovered. Aggression accompanied by elevations (p<0.05) in cortisol concentrations occurred in all grouped sows on the first day of grouping. The cortisol increase was greater (p<0.01) in the subord inate than in the other ranked sows. Cortisol concentrations and the l evel of aggression decreased on subsequent days during grouping, but t he cortisol levels were still higher than on the pre-grouping day exce pt for the intermediate ranked sows. Cortisol concentrations after the ACTH test were similar in the grouped as well as the control sows. Th e dominance hierarchy was confirmed during the rank order test. Concen trations of P-4, E(2), PG-metabolite and CBG were similar between the group-housed sows and with the controls. Mean embryonic recovery was 6 6.8% +/- 11.5%, 71.3% +/- 6.0%, 70.0% +/- 16.0%, and 69.9% +/- 5.8% fo r the dominant, intermediate, subordinate, and control sows respective ly. Hence, group housing during early pregnancy did not influence repr oductive hormones or embryonic survival.