Genetic parameters for production traits and somatic cell score of the SA Dairy Swiss population

Abstract

The SA Dairy Swiss population could not previously be incorporated into the National Dairy Genetic Evaluation System, owing to inadequate population numbers and data structures. However, in recent years participation in Milk Recording has improved sufficiently to allow for genetic evaluation of the population. The aim of the study was therefore to estimate genetic parameters for the SA Dairy Swiss for production traits and somatic cell score in order to estimate breeding values routinely from the National Dairy Genetic Evaluation System. After editing procedures, a dataset of 25 621 test-day records for milk, butterfat and protein yields and a dataset of 10 438 test-day records for somatic cell count were obtained for further analysis. (Co)variance components for milk (kg), butterfat and protein yields (kg), as well as for somatic cell score, were estimated using a fixed regression multi-lactation animal model, based on test-day records of the first three lactations. Records from the various lactations were included as repeated measures. A multi-trait evaluation was performed for the production traits, while a single trait evaluation was done for somatic cell score, using the software package VCE4. Heritability estimates were 0.19 for milk, 0.16 for butterfat, and 0.16 for protein yields. The heritability estimate for somatic cell score was lower, at 0.07. The genetic correlations between the production traits were lowest for milk and butterfat (0.83), and were similar for milk and protein (0.94) and butterfat and protein yields (0.94). These values compare favourably with those of the other South African dairy breeds, based on the same model. The (co)variances were then implemented for estimation of breeding values for the SA Dairy Swiss population. Genetic trends were favourable for milk production traits with milk yield, butterfat and protein yields increasing by 25.13 kg/year, 0.96 kg/year and 0.79 kg/year, respectively; while the trend for somatic cell score was unfavourable, increasing by 0.86 units/year, since 1983. The SA Dairy Swiss could therefore be incorporated into the National Dairy Genetic Evaluation System of South Africa, using these covariance components and model.