Effects of oestradiol benzoate treatment on the reproductive performance and endocrine status of sows after lactations of 10 or 35 days

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Abstract
Landrace .times. Large White sows (42) were used in 3 studies of estradiol benzoate treatment 24 h (E1) or 48 h (E2) after piglet removal, following lactations of 10 (S) or 35 (L) days, or were untreated controls (C). For Exp. [experiment] 1, estradiol benzoate doses were 4, 16 and 64 .mu.g/kg body weight; since highest mean LH [luteinizing hormone] peaks followed use of the 16 .mu.g/kg dose, this treatment was used in later studies. Treatments for Exp. 2 were S-E1 and L-E1 (N = 3). Pregnancy rates were 1/3 and 2/3, respectively, while 10-day weaned sows tended to have longer weaning-remating intervals, shorter estrous periods and lower post-injection estradiol peaks. Post-treatment LH peaks were recorded from all L-E1 sows, but only one S-E1 animal. Treatments S-E2, L-E2,S-C and L-C (N = 6) were used in Exp. 3; pregnancy rates were 1/6, 6/6, 5/6 and 6/6, respectively, while peak estradiol levels were 49.5 .+-. 8.3, 74.8 .+-. 15.1, 21.7 .+-. 2.0 and 51.8 .+-. 26.5 pg/ml, respectively. Weaning-remating intervals were extended in S-C sows (P < 0.05), while estradiol treatment prolonged behavioral estrus. LH peak values were reduced after short lactations, but not affected by estradiol treatment. Plasma prolactin concentrations at weaning were higher in sows in treatment S than in treatment L, while at the subsequent estrus in estradiol-treated sows they were elevated more and for longer periods than in controls. Reduced gonadotropin secretion and fertility after short lactations are not overcome by treatment with estradiol benzoate.

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