Materials and methods: Multiparous sows were randomly assigned to treatment at weaning. From weaning, twice-daily boar exposure facilitated estrus detection. Untreated control sows (n = 150; CONT) were artificially inseminated at least twice. Treated sows (n = 168; LUT) received 5 mg pLH intramuscularly concomitant with the first detection of standing heat. To coincide with the normal working day, sows in estrus in the morning were inseminated at 24 and 30 hours (am and pm), while sows in estrus in the afternoon were inseminated at 24 and 42 hours (pm and am), after pLH administration.
Results: For multiparous sows bred on days 4 to 6 after weaning, total-born litter size was greater in LUT than in CONT (12.88 and 11.80, respectively; P < .01), whereas adjusted farrowing rate was not affected by treatment, (LUT, 87.28%; CONT, 83.20%; P > .05). Neither variable was affected by day of breeding or a treatment × day interaction (P > .05). Fewer inseminations (P < .001) were performed in LUT (2.00) than in CONT (2.13).
Implication: Double insemination of multiparous sows, timed to coincide with optimal sow fertility, may improve litter size.
Zak LJ, Patterson J, Hancock J, et al. Benefits of synchronizing ovulation with porcine luteinizing hormone in a fixed-time insemination protocol in weaned multiparous sows. J Swine Health Prod. 2010;18(3):125–131.