Progress with the control of oestrus and ovulation in farm livestock

No Abstrac

Estimation of genetic variation in the interval from calving to postpartum ovulation of dairy cows

Data on the interval from calving to the commencement of luteal activity of postpartum dairy cows were obtained for 1737 lactations of 1137 British Friesian cows in 11 commercial herds and 1 experimental herd between 1975 and 1982. The interval from calving to commencement of luteal activity was measured using progesterone concentrations of milk samples that were collected three or more times per week from shortly after calving to approximately 100 DIM of the following gestation. Genetic models were fitted using REML and accounting for known genetic relationships. Estimates of heritability and repeatability were 0.28 and 0.28, respectively, for the untransformed data; 0.21 and 0.26, respectively, for log-transformed data; and 0.13 and 0.26, respectively, after reciprocals were considered. In all cases, the heritability was significantly different from 0, and, of three scales, the log transformation had the greater likelihood. The Likelihood of the transformation was closely related to the magnitude of the coefficient of skewness, and the power transformation with maximum likelihood was between 0.35 and 0.30, for which heritability was 0.19. The geometric mean interval was 25.6 d; coefficient of variation was 37%; and herds, years, parity, and season all had significant effects upon the interval to commencement of luteal activity. The postpartum interval grew longer by 2.2% with each parity [confidence interval 95% (1.1%, 3.0%)] and showed seasonal variation. Cows calving during spring took 1.21 times longer to commencement of luteal activity than did cows calving during autumn [95% confidence interval (1.13, 1.29)]. Genetic regression on PTA of the sire for milk, fat, and protein yields and for fat and protein percentages and on a national economic index were carried out using a subset of animals during 721 lactations. The regression was positive for fat percentage, but not significantly different from 0 for others. The magnitude of the heritability estimate in this study indicates that the postpartum interval to commencement of luteal activity may be useful for selecting cattle for improved fertility because shorter intervals have been postulated to be correlated with higher reproductive efficiency

The application of new techniques for the control of growth in farm livestock

The recent EEC Directive banning the use of anabolic agents as growth promoters in animal production in countries of the EEC and, by implication, prohibiting imports of fresh and processed meats from countries not applying a similar ban, has raised undue concern by research scientists involved in studies of the biochemistry and physiology of growth promoters. In addition to the well established growth response and improved carcass composition obtained from using anabolic agents (both naturally occurring hormones and zenobiotic compounds), there are exciting developments involving new pharmacological agents, new immunological techniques and the possibility of direct manipulation of the genome.</jats:p