Boar contact is an effective stimulant of ovulation during early lactation

The efficacy of 400IU equine chorionic gonadotrophin (eCG) and 200IU human chorionic gonadotrophin (hCG) (PG600; Intervet, Australia) and boar exposure as stimuli of oestrus and ovulation have been established in pre-pubertal gilts and weaned sows, but there is little published data on their use to overcome lactation anoestrus. Designed as a 2×2 factorial, the current study used 40 Large White/Landrace sows (parity 1.9±0.14), to determine the effects of boar exposure (BE) versus NoBE and PG600 versus NoPG600 on the incidence of lactation oestrus and ovulation. On day 1 of lactation, PG600 was administered and BE commenced. Throughout lactation all sows were housed individually in farrowing crates (0.6×2.4m²). BE consisted of 15min of daily, full physical boar exposure in a detection mating area. For all sows, litter size suckled was standardized to 10 piglets on day 1 of lactation, and maintained at this level until weaning on day 26 post-partum. Oestrus detection was performed daily, with oestrus defined as the exhibition of a standing reflex, and ovulation confirmed when progesterone concentrations exceeded 1.0ng/ml on day 3 and 4.0ng/ml on day 10 post-oestrus detection. There was no effect of PG600 on any reproductive measures, and no interactions with the BE treatment. A higher proportion of BE compared to non-BE sows exhibited a behavioural oestrus without ovulation within 5 days of parturition (0.83 versus 0.09; P<0.05). The interval from parturition to lactation ovulation was unaffected by treatment (15.4±1.21 days). However, BE increased the proportion of sows ovulating during lactation (0.61 versus 0.09; P<0.05), and resulted in an earlier ovulation relative to parturition (20.6±1.30 versus 30.1±1.35 days) compared to non-BE sows. In conclusion, this is the first study to demonstrate that taking lactating sows to a detection mating area for 15min of daily, physical boar contact resulted in a high incidence of lactation ovulation within 22 days of parturition.