Oestrus synchronization and fixed-time artificial insemination in the weaned sow

Abstract

Reproductive performance was assessed in multiparous weaned sows in which double fixed-time AI was used in association with the injection of oestradiol benzoate (OB) to synchronize post-weaning oestrus. After weaning (day 0), groups of 25 sows were either injected with ethyl oleate (group 1, controls), or 10μg OB/kg body weight (b. wt.) (group 2) on the morning of day 2, or 10μg OB/kg b.wt. on the morning of day 3 (group 3). Group 1 sows were inseminated 8–16 h after the onset of behavioural oestrus and again 24 h later. Group 2 and 3 sows were inseminated on the afternoons of days 4/5 and 5/6, respectively. Sows were allocated to treatment with respect to parity and litter-size born, and no differences existed in pre-treatment reproductive performance between groups. The mean weaning-to-oestrus interval in group 1 sows was 5.66 ± 0.14 days; 49/50 OB-treated sows were in oestrus when inseminated, indicating the efficacy of OB in promoting an early and synchronous return to oestrus. Conception rates were 19/25, 8/25 and 14/25 for groups 1, 2 and 3, respectively, and the difference between groups 1 and 2 was significant (ifP< 0.01). Ovulation rates, assessed in pregnant sows at 28 to 40 days of gestation, were not significantly different (18.32 ± 0.76, 17.00 ± 0.93 and 16.64 ± 0.83 for groups 1, 2 and 3, respectively) but embryonic survival was affected by OB treatment and was significantly lower (ifP< 0.01) in group 2 (36.8%) than in control (64.4%) sows. In non-pregnant sows the ovulation rate at slaughter was similar in all groups, indicating that there was no residual effect of OB treatment on ovarian function. Five of the group 2 sows had cystic follicles at slaughter. It is concluded that the time of oestrogen treatment after weaning has a critical effect on reproductive performance in the sow. Work on further refinements of the dose and mode of administration of oestrogen, as well as the timing of injection in individual herds is, therefore, needed in order to determine whether treatment with oestradiol can be effectively used for oestrus synchronization in association with fixed-time mating or AI.