Methodology has been developed to implement testday models in the national genetic evaluation of dairy breeds for production traits in South Africa. Positive definite covariance matrices have been estimated, using multitrait, multi-lactation, fixed regression testday BLUP animal models, including testday records of the first three lactations as repeated measures for the Holstein and Jersey breeds. Heritability estimates were 0.40 ± 0.007 for milk yield, 0.25 ± 0.006 for butterfat yield and 0.37 ± 0.006 for protein yield for the Holstein breed and 0.39 ± 0.004 for milk yield, 0.21 ± 0.002 for butterfat yield and 0.34 ± 0.002 for protein yield for the Jersey breed. These estimates are well in the range of estimates reported by countries participating in INTERBULL evaluations.
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