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 programme. The study was conducted during the breeding period (May-October), and cows were inseminated with freshly prepared Friesian semen when they stood to be mounted by the vasectomised bull or herdmates. Fertility was measured by 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 classified into short, normal and long cycles. The mean duration for short, normal 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 returns 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% conceived to the second breeding. Five and nine cows became acyclic after the first and second breeding, respectively, constituting 22. 0%. Cows that displayed 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 acyclic 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 conceive may be rebred.