Fertilisation and embryonic survival rates in dairy cows culled as repeat breeders.

Seventy-three Friesian dairy cows culled as repeat breeders were slaughtered three to six, 16 to 19 or 40 to 49 days after insemination to establish fertilisation and embryo survival rates. Fertilisation rate following a single insemination was 72 per cent. The estimated embryo survival rates for days 16 to ¿19 and 40 to 49 were 67 per cent and 76 per cent, respectively. The previous breeding history of the cows showed that only eight (11 per cent) had consistently regular returns (18 to 24 days) to service. Fifty-three (75 per cent) had a combination of both long and short returns to service. Before service on experiment, 64 (89 per cent) cows had regular cycles and the six cows which repeated from the 40 to 49 days group, five (83 per cent) had regular return intervals. It is suggested that errors in oestrus detection contribute substantially to the problem of repeated returns to service of dairy cows in Ireland.

Hormonal control of the bovine oestrous cycle.

PIP: The role of hormones in controlling the estrous cycle of cows is reviewed in the context of current research, specifically on endocrinal functions. This is central as the follicles grow on the ovaries in response to the pituitary's follicular stimulating hormone. When the ovaries produce sufficient estrogens, an ovulatory surge of luteinizing hormone is released by the pituitary. This causes the ovulation of 1 of the follicles and the growth of a corpus luteum in the follicular cavity. This corpus luteum secretes progesterone for about 2 weeks until its activity is terminated by uterine luteolysin. Control of the estrous cycle thus depends on alternate signals from the pituitary and ovaries with the end of the cycle caused by the nonpregnant uterus.^ieng