Genetic evaluation of Holstein-Friesian and Jersey sires using records from pure- and cross-bred progeny in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in animal science at Massey University
Milk Yield, Milk Fat Yield, Milk Protein Yield and Days in Milk of 72,480 dairy cows of Holstein-Friesian, Jersey and their reciprocal crossbred were analysed. The main objective of this study was to investigate possible use of crossbred progeny records to genetically evaluate sires. Bulls of each breed were evaluated separately using their purebred, crossbred or both purebred and crossbred progeny. First, crossbred progeny were used without including genetic groups. Secondly, crossbred progeny were used with genetic groups included. Rank correlations for different types of evaluations were calculated. In total, 10 different comparisons, 5 for each breed, were performed. The expected correlation of ranks of sires obtained using different data sets were estimated where applicable. Reliability and Prediction Error Variance of sire proofs were estimated both by an approximate method and direct calculation. Over-estimation of reliability and under-estimation of Prediction Error Variance by the approximate method was given. High correlations between ranks of Holstein-Friesian sires evaluated using different data sets were observed, while, the correlation between ranks of Jersey sires evaluated using purebred progeny with ranks of the same sires evaluated using only crossbred progeny was less than expected. Correlations of ranks of Jersey sires evaluated using all progeny with ranks of the same sires evaluated using only crossbred progeny were also low. After plotting EBVs of sires of each breed obtained using only purebred against EBVs of the same sires obtained using both purebred and crossbred progeny, two lines with slightly different slopes were observed. The reasons for the formation of these two lines were investigated. It was found that the number of effective crossbred progeny of sires was affecting the regression of EBVs of sires obtained using all progeny on EBVs of same sires obtained using only purebred progeny. It was concluded that crossbred progeny of Holstein-Friesian sires may be used to assist in their evaluation under New Zealand conditions, but, further research is recommended before using crossbred progeny of Jersey sires in sire evaluation.