Lactation estrus and subsequent fertility in group housed lactating sows

NetherlandsOne way to improve post-weaning piglet welfare, is to prolong the lactation period. However, as sows are normally anestrus during lactation, a prolonged lactation will result in a reduction in the number of piglets produced per sow per year. It is possible to induce a fertile estrus during lactation using an intermittent suckling strategy (IS). This is a management strategy inwhich the daily suckling frequency is reduced by limiting the time sows and piglets spend together. This study evaluated effects of IS in the 5th week of a 6-week (batch 1-4) or 9-week (batch 5-9) lactation period on reproductive performance of group-housed lactating sows. Per batch, 4-5 multiparous sows were housed in a multi-suckling system. IS started after four weeks of lactation (= IS-Day 0) and sows were separated from their piglets 10 hours per day for 7 days. During separation, sows were housed inan adjacent IS-area, where a boar was present in a boar pen. In the IS-area, the back-pressure test was applied to sowstwice a day in presence of the boar to detect estrus.Sows were inseminated daily during standing estrus.After week 5, sows had voluntary access to the IS area 24 hours per day. At IS-Day 0 and IS-Day 5, transrectal ultrasound was used to assess ovarian status and to measure the 5 largest follicles per ovary. A pregnancy check was performed 4 weeks after insemination. In total, 34out of 44sows (77%)came in estrus at 5.2±1.5(3-9) days after onset of IS. One additional sow came in estrus in week 7 of lactation. In total33of the 34sows that showed estrus during IS ovulated(97%). Ovulating sows of Batch 1-8 had an 89% (25/28) farrowing rate and a subsequent litter size of18.1±3.3.The sows of Batch 1-8that came in estrus during IS had a larger follicle size at IS-Day 0 (3.6±0.4 vs 3.2±0.4 mm, P=0.01) and at IS-Day 5 (6.2±0.8 vs 5.3±0.9 mm, P=0.01) than sows that did not show estrus. They also had more backfat at IS-Day 0 (14.2±2.9 vs 11.5±3.0 mm, P=0.01); 90% of the 21 sows with a backfat >12.5mm came in estrus compared to 50% of the 18 sows with lower backfat. There was no difference in sow parity (3.2±1.6), sow weight at IS-Day 0 (222±30kg) or litter size at IS-Day 0 (11.6±1.7) between sows that did and did not come in estrus during IS. In conclusion, IS can be a good method to induce lactation estrus and pregnancy in group-housed lactating sows, resulting in good litter size. Sows should be in a good body condition at onset of IS to increase the chance of estrus induction. These findings are a promising step for the further development of systems with longer lactation periods while safeguarding the number of piglets produced per sow per year.