Two hundred sows were randomly assigned to intramuscularly receive 0.9% NaCl (group 1) or oxytocin 0.083, 0.11 or 0.17 IU/kg (groups 2, 3 and 4, respectively) immediately after the expulsion of the first piglet. The overall duration of labor was decreased in a dose-dependent relationship. Time interval between piglets was decreased approximately 5 min in groups 3 and 4 while sows in these groups exhibited approximately 10-20 contractions x 10 births more than controls (P<0.005). Duration and intensity of uterine contractions also showed a positive dose-response relationship. As an indicative of fetal distress, approximately 2.5 times more meconium-stained piglets were born to sows receiving the higher doses of oxytocin, but in the lowest dose significantly decreased. Oxytocin 0.083 IU/kg significant decreased the mortality rate of piglets [OR 0.49 (95%CI, 0.26-0.92)]. In conclusion, we recommend the intramuscular administration of the lowest possible dose of oxytocin, which still decreases the duration of labor in sows.