Induction of estrus in lactating Zebu x Friesian dairy cows with cloprostenol

Abstract

Four trials were conducted in a herd of lactating Zebu x Friesian cows, raised in Ribeirão Preto, São Paulo, Brazil, investigating induction of estrus through 0.5 mg of Cloprostenol (ICI 80,996) given intramuscularly. Each cow, 71 treated and 66 controls, was rectal palpated for the presence of an active corpus luteus before treatment. In the first trial, starting in october, 31^th, 1977 cloprostenol injection was given on day 0 and repeated on day 11 for those animals which had not already shown heat and been inseminated. In the second, third and fourth trials, a single injection was given on january, 9^th; february, 11^th and march, 18^th, 1978. Estrus was observed during the first seven days and up to 28 days after treatment in both treated and control animals. Cows were submitted for insemination when observed in estrus. Results were based on pregnancy diagnosis from 45 to 50 days following the inseminations. In treated animals, 54.9% were recorded as being in estrus within 7 days and 70.4% within 28 days, while in control animals, these data were 13.6% and 37.8%, respectively. Pregnancy rate in treated animals was 32.3% (7^th day) and 53.5% (28^th day), compared to 10.6% and 19.6% among the control cows. The use of cloprostenol may be valuable in dairy herds where the detection of estrus is difficult.