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Post-weaning fertility failures occur more often in parity 1 (P1) sows due to increased metabolic demands for lactation and inability to meet energy requirements for maintenance, growth, and reproduction. We hypothesized that body condition loss occurs more frequently in P1 sows nursing a large litter, resulting in impairment of ovarian follicle development during lactation and post-weaning. At 24 h post-farrowing, P1 sows (n = 123) were assigned to treatment (TRT) based on body weight and the number of functional teats to receive High Number (HN, 15 to 16) or Low Number (LN, 12) of nursing pigs. At weaning, sows in each TRT were assigned to receive PG600 or None (Control). During lactation, sow body measures were obtained and ovarian follicles were assessed in mid-lactation and post-weaning. Lactation data were analyzed for the effects of TRT, and fertility data after weaning were assessed for TRT x PG600. There were no interactions of TRT x PG600. During lactation, 22.2% of HN sows lost ≥4 pigs and were removed from analysis. The HN sows lost more (P &amp;lt; 0.05) body weight (-6.2 kg), backfat (-1.0 mm), body condition score (-0.4), and nursing piglets (-0.4) than LN sows. However, HN sows weaned more pigs (14.0) than LN sows (11.0). There was no effect of TRT on wean to estrus interval (4.2 d), but was 0.5 d shorter for PG600 (P = 0.004). There were no effects of TRT or PG600 on estrus within 6 d after weaning (85.6%), but PG600 induced smaller (P = 0.002) follicles at estrus (6.7 mm) than Control (7.3 mm). In the subsequent parity, there were no effects of TRT or PG600 on farrowing rate (93.9%) and total born (13.2). Overall, HN sows lost more piglets and body condition, although they weaned more pigs, but had no effects on reproductive performance.

174 Effects of Nursing a Large Litter and Ovarian Response to Gonadotropins at Weaning on Subsequent Fertility in First Parity Sows