Development of a Temperate Dairy Cattle Breeding Programme in Sri Lanka Using Milk, Fertility and Udder Health Traits

Abstract

<p>This thesis aimed to lay a foundation for a dairy cattle breeding programme in tropical Sri Lanka using temperate dairy breeds. The fundamental requirements for establishing a dairy breeding programme were studied, i.e. genetic parameters and economic values were estimated, and response to selection was predicted for milk production, udder health, and fertility traits in imported Jersey and Jersey-Friesian crossbred cows in Sri Lanka. Heritability estimates of predicted and realized 305-day milk yield traits ranged from 0.02 ± 0.01 to 0.09 ± 0.02, and heritability estimates for daily milk yield records ranged from 0.002 ± 0.05 to 0.19 ± 0.02 in first lactation. These heritability estimates were low mainly due to the low additive genetic variance. The correlations between the estimated breeding values for 305-day milk yield for bulls in Australia and bull estimated breeding values based on their progeny in Sri Lanka were 0.39 in Jersey cows and -0.35 in Jersey-Friesian cows, suggesting that importing genetic material from Australia to the population in Sri Lanka is not an effective route for genetic improvement. All mastitis traits had a zero heritability. Milk electrical conductivity and milk flow rate are often used as potential indicator traits in selection for mastitis resistance. In this study, milk electrical conductivity and milk flowrate were lowly to moderately heritable with heritability estimates ranging from 0.02 ± 0.01 to 0.11± 0.03 and from 0.02 ± 0.01 to 0.14 ± 0.04. Mastitis had no phenotypic association with milk electrical conductivity and only lowly negative phenotypic correlations with milk flowrate (range -0.17 to 0) demonstrating that milk electrical conductivity or milk flow rate were not good indicators of clinical mastitis in this study. The reproductive traits analysed were the interval from first calving to first service, the interval from the first service to conception, the interval from first calving to conception (days open), the interval between first calving to second calving, gestation length, number of services per conception for second calving and stillbirths. The heritability estimates for fertility traits ranged from 0.01 ± 0.01 to 0.05 ± 0.02, and they were sufficiently heritable to be used in a breeding programme. Genetic improvement of milk yield, age at first calving, number of services per conception, calving interval, and number of mastitis episodes had a positive impact on the farm profitability while genetic improvement of fat and protein yields was not profitable due to high feed cost relative to the additional returns. Percentage change of the traits relative to the current mean after one year of selection for annual milk yield, annual fat yield, annual protein yield, age at first calving, number of services per conception, calving interval, and mastitis episodes were 0.40, 0.34, 0.67, 0.34, 0.31, -0.18 and 0.21, respectively. </p> <p>Favourable responses to selection were observed for milk, fat, and protein yields, and calving interval. Genetic improvement of milk, fertility, and mastitis traits should be included in the breeding objective for temperate dairy breeds in large-scale intensive dairy farms in Sri Lanka. Proposed structure and function for implementing a single across-herd genetic evaluation for temperate dairy cattle in Sri Lanka, and recommendations for routine data collection were provided.</p>