Effect of Oxytocin, Cloprostenol or Buserelin in Semen Doses on Sow Fertility

During the periods January to April, May to August, and September to December in two consecutive years, sows were assigned at breeding to receive semen doses supplemented with 87 µg cloprostenol (PG; n = 158), 5 IU oxytocin (OT; n = 154), 2 µg buserelin (GN; n = 93), or served as non-supplemented controls (CON; n = 605). Sows were inseminated at the detection of estrus, and again 24 h later, but only the first inseminations were supplemented. Compared to CON, only buserelin increased pregnancy and farrowing rates (p ≤ 0.05); there was no effect of a period or a treatment × period interaction. Litter size was larger (p ≤ 0.001) for all seminal additive groups during the first two periods and tended to increase in GN compared to CON (p ≤ 0.1) during the third period, resulting in a tendency (p < 0.1) for a period × treatment interaction. The addition of cloprostenol, oxytocin or buserelin to semen doses at first insemination increases litter size in multiparous sows.