A ‘two-stage’ farrowing and lactation system: assessing the impacts of group lactation on the incidence of lactational oestrus and reproductive performance

Piglet removal for 16 hours per day from d 16 after parturition onwards, combined with fence-line boar exposure, stimulated a high proportion of crated sows to exhibit a synchronous ovulatory response during lactation (Downing et al. 2011). However, it is still unclear whether the natural separation of sows and piglets in a group housing system would induce a similar response (van Nieuwamerongen et al. 2014). This study tested the hypothesis that an increase in follicular development and spontaneous oestrus would be observed amongst group-housed sows during lactation compared to crated- and PigSAFE-housed sows.

Mixed-parity sows (Large White x Landrace, PrimeGro™ Genetics; n = 160) over six time replicates were allocated to one of four treatment groups 14 days before weaning: Farrowing crates (FC): sows housed in farrowing crates until weaning; GL_FC: sows housed in farrowing crates then moved into group lactation 14 days before weaning (six sows/replication); PigSAFE (PS): sows housed in the PigSAFE loose farrowing system until weaning; and GL_PS: sows housed in the PigSAFE system then moved to group lactation 14 days before weaning (six sows/replication). In the 14 days before weaning, 24-hour daily video footage was recorded over the two group lactation pens. Signs of sexual behaviour, including mounting and ano-genital sniffing, were recorded. Ovarian follicle development was measured once 7 days before weaning and once at weaning, using rectal ultrasound (focal sows, n = 36/treatment). Blood was collected from focal sows 4 days after weaning for analysis of progesterone concentration. Sows were mated on their first return to oestrus after weaning. Data were analysed using Chi-square and post-hoc Bonferroni (IBM SPSS, Version 21.0; USA).

The average WRI showed a weak tendency (P = 0.155) to be shorter in FC sows, and more FC sows were mated within 4 days of weaning (P = 0.049) (Table 1). The progesterone concentration data, together with the WRI, indicated no statistical difference (P > 0.05) that sows in PigSAFE and group lactation systems experienced a higher incidence of lactational oestrus and ovulation compared to farrowing crates. The combination of oestrus behaviour signs, ovarian follicular size, increased WRI and progesterone concentrations suggest that between 3.1 and 20.7% of sows across all treatments experienced lactational oestrus and perhaps ovulation, possibly as a result of shifting suckling patterns. In a ‘two-stage’ lactation system, strategies to manage for spontaneous ovulation seem essential and could be achieved by further stimulating the sows through piglet separation and (or) boar exposure, so that the majority of sows can be mated during lactation.

Table 1.  Reproductive performance of sows in two-stage lactation systems, crates and PigSAFE. Values are mean ± SD (where indicated)