Serum progesterone profiles of zebu cattle (Bos indicus) in relationship to conception and repeat breeding after artificial insemination

Sixty-four zebu cows, comprised mainly of Bunaji cattle aged between 3 and 7 years old, were involved in an intensive artificial insemination programm e. The study was conducted during the breeding period (May-October), and co ws were inseminated with freshly prepared Friesian semen when they stood to be mounted by the vasectomised bull or herdmates. Fertility was measured b y serum progesterone (P-4) concentrations and pregnancy diagnosis by rectal examination post-insemination. From the records of oestrus detection and P -4 profiles of cattle following breeding, 39 oestrous cycle lengths were cl assified into short, normal and long cycles. The mean duration for short, n ormal and long oestrous cycles were 15.6 +/- 2.0, 21.5 +/- 1.5 and 29.5 +/- 2.5 days, respectively. Mean inter-oestrus intervals between the treatment groups were not different. The percentage frequency distribution was 48.7% for normal oestrous cycles. The short oestrous cycle lengths of 11-17 days were observed in 12.8% of the cases, while 38.5% of the cases of oestrus r eturns had long luteal phases with oestrous cycle lengths of 26-32 days. Out of the 64 cows, 48.4% conceived to the first breeding while 18.8% conce ived to the second breeding. Five and nine cows became acyclic after the fi rst and second breeding, respectively, constituting 22.0%. Cows that displa yed irregular oestrous cycles (repeat breeders) constituted 10.9%. Average number of services per conception was 1.3. Serum P-4 is of practical value in monitoring ovarian activity in cattle and in the identification of acycl ic and repeat breeder cows. Repeat breeder cows could be investigated by a combination of radioimmunoassay and clinical examination of the ovaries and reproductive tract. In cattle management, it is economical and profitable to diagnose pregnancy early after insemination so that cows which fail to c onceive may be rebred. (C) 2000 Elsevier Science B.V. All rights reserved.