Intermittent suckling with primiparous sows: skip-a-heat effects on oestrus during lactation, reproductive performance and embryo survival

Research in Europe and Australia has demonstrated that oestrus can be evoked during late lactation by periodic separation of sows and piglets combined with boar contact, and that mating during lactation results in pregnancy rates and subsequent litter sizes comparable to that of conventionally weaned multiparous (MP) sows (Soede et al. 2012; McDonald et al. 2013). However, there is limited data available on primiparous (PP) sows, and because this is a category of sows that is generally challenged metabolically during lactation (more so than MP sows), this may have negative effects on lactational oestrus response rates and subsequent reproductive outcomes. Therefore, it was hypothesised that mating PP sows at the subsequent oestrus following their first oestrus during lactation (skip-a-heat) would improve reproductive performance and embryo survival when combined with an intermittent suckling oestrus induction protocol.

Primiparous sows (Large White × Landrace, Hypor genetics; n = 76) were allocated to either a Control treatment (C28), where piglets were weaned at d 28 of lactation, or an intermittent suckling treatment (IS21), where all piglets were separated from the sow for 8 h/d from d 21 of lactation until weaning at d 28. The IS21 sows were housed in group pens during the separation period and received twice-daily fence-line boar exposure in a detection mating area. Sows were mated at either lactational oestrus, or at the subsequent oestrus following lactational oestrus (skip-a-heat). The C28 sows and any IS21 sows that did not experience a lactational oestrus (non-responders) were mated at their first post-weaning oestrus. At approximately d 30 of gestation the sows were slaughtered on site to examine embryo characteristics. A mixed model was used to analyse effects of treatment on reproductive parameters (SAS^®; USA). Pregnancy rate was analysed separately using the generalised logit function of SAS.

Ovulation rate and embryo survival between PP sows mated at their first oestrus during lactation and at the subsequent oestrus following lactational oestrus (skip-a-heat) differed (P < 0.05), however this did not cause a difference in the number of viable embryos at d 30 (P > 0.05; Table 1). Interestingly, mating at the first oestrus during lactation reduced (P < 0.05) placental development and embryonic weight at d 30 compared to C28 sows, with skip-a-heat sows and non-responder sows being intermediate (Table 1). Overall, skip-a-heat mating compared to mating at the lactational oestrus did not significantly improve reproductive performance or embryo survival in PP sows. However, the effect of lactational oestrus on subsequent litter development requires further examination.

Table 1.  Lactational oestrus and subsequent reproductive outcomes in primiparous sows mated at lactational oestrus (first heat), at the subsequent oestrus following lactational oestrus (skip-a-heat), or at normal post-weaning oestrus (non-responders). Values are the least-squares mean ± SEM