INVESTIGATION OF THE RELATIONSHIP BETWEEN FARROWING ENVIRONMENT, SEX STEROID CONCENTRATIONS AND MATERNAL AGGRESSION IN GILTS

Maternal oestrogen and progesterone have been shown to be important in the initiation of maternal behaviour. Thirty-three Large White x Land race gilts, housed in groups during pregnancy, were observed and aggre ssive interactions recorded. Individuals had jugular catheters implant ed 14.5 (s.e. 0.34) days before their expected parturition date (EPD). Five days before EPD gilts were randomly allocated and moved to eithe r a conventional farrowing crate (C; without straw, 16 gilts) or a pen (P; 2.1 x 3.1 m(2); with straw bedding, 17 gilts). Blood samples were taken at frequencies determined by the proximity to farrowing onset. Piglets were removed at birth and returned 2 h after placental expulsi on. The reaction of each gilt to her piglets was monitored. Gilts sava ging piglets were sedated with azaperone (n = 8). There was no overall effect of farrowing environment on oestradiol and progesterone concen trations. The pre-farrowing ratio of progesterone to oestradiol was hi gher for (P) gilts (0.45 vs. 0.25, (P) vs. (C); S.E.D. 0.085, P < 0.05 ) as was their overall maximum oestradiol level (3.39 vs. 2.29 ng/ml, (P) vs. (C); S.E.D. 0.39, P < 0.01). In contrast to progesterone, oest radiol patterns varied considerably between individuals. Dominance ran k value during pregnancy, but not levels of aggression, correlated pos itively to pre-farrowing oestradiol concentrations. Treatment with aza perone was not related to farrowing environment, piglet weight or litt er size. Azaperone treated gilts showed a higher pre-farrowing oestrad iol to progesterone ratio (0.55 vs. 0.29, +/-azaperone; S.E.D. 0.10, P < 0.05), significantly higher levels of oestradiol post-partum (0.7 v s. 0.19 ng/ml, +/-azaperone; S.E.D. 0.20, P < 0.001) and significantly lower levels of aggression during pregnancy (1.68 vs. 2.23 aggressive interactions /h, +/-azaperone; S.E.D. 0.15, P < 0.001). The results i ndicate that there are no major effects of farrowing environment on se x steroid concentrations. Maternal aggression under these conditions a ppears to be negatively related to aggression during pregnancy, but th is is not reflected in plasma concentrations of sex steroids around pa rturition. (C) 1998 Elsevier Science B.V.