Endogenous oxytocin is released by the sow at the time of mating in re
sponse to stimulation by the boar, which may explain, at least partial
ly, the importance of the relationship between the boar's courting act
ivity and the subsequent reproductive performance of the sow. The aim
of this study was to determine the effects on reproductive performance
of supplementing AI doses with exogenous oxytocin during the low fert
ility season. At an intensive piggery in northwest Spain 3 experimenta
l groups were randomly formed and observed throughout the year. Group
1 sows were inseminated with semen supplemented with 4 IU oxytocin. Gr
oup 2 sows received 4 IU oxytocin injected through the vulvar lips muc
osa at the time of insemination. Group 3 sows were inseminated without
oxytocin and served as the controls. During the low fertility season
the results for each group were as follows: farrowing rate 77.02, 56.2
5 and 54.39%, and litter size 10.77+/-0.28, 10.45+/-0.31 and 8.53+/-0.
34 respectively. It is concluded that the addition of oxytocin to semi
nal doses just before AI is an easily applicable, effective method for
increasing fertility and litter size during the summer months. (C) 19
98 by Elsevier Science Inc.