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Two series were used in studying the use of a low dose of intravaginal cloprostenole in oestrous synchronisation of zebu cows. In series I, 39 cows were given 175 mcg of cloprostenole with a plastic catheter in the anterior vagina twice, with a 12-day interval. After treatment, 61.5% of these cows came into heat, were inseminated and 70 days later pregnancies were confirmed in 66.6% of inseminated cows. In series II, intravaginal treatment (40 cows) was compared with intramuscular administration (33 cows) of 500 mcg of cloprostenole. After treatment the cows were checked for silent heat in addition to visible heat. The overall oestrous response, for both visible and silent heat, was 62.6% and 60.6% after the intravaginal and the intramuscular treatments respectively, and there was no statistical difference between the 2 treatments. Unfortunately the pregnancy of the cows could not be checked. Intravaginal administration of 175 mcg of cloprostenole resulted in good oestrous synchronisation and pregnancy rate. For zebu cattle, the oestrous synchronisation response was similar to that reached with 500 mcg of cloprostenole administered intramuscularly.