GENETIC-PARAMETERS FOR MILK-PRODUCTION AND BODY SIZE IN NEW-ZEALAND HOLSTEIN-FRIESIAN AND JERSEY

178 and 128 half-sib groups of 7345 Holstein-Friesian and 3967 Jersey primiparous cows were milk recorded and body size traits subjectively assessed. In the analysis models differing with respect to the sire effect were used to assess the effect of selection of ancestors. Heritabilities for milk fat, protein and milk were 0.26, 0.26 and 0.28 for Holstein-Friesian and 0.26, 0.24 and 0.26 for Jersey, respectively. Body weight and stature showed heritabilities of 0.24 and 0.29 for Holstein-Friesian and 0.16 and 0.23 for Jersey, which are comparable to those for yield traits. This indicates that current breeding schemes could be used to genetically influence body size traits. Heritability estimates for all production traits consistently increased in both breeds when paternal grandsires were included in the model, thus alleviating the effect of selection. Genetic correlations between yield traits were large and positive, ranging from 0.68 to 0.87. With estimates ranging from 0.29 to 0.46, body weight and stature were moderately and positively genetically correlated with milk fat, protein and milk yields in both breeds, indicating that body size traits could be considered as selection criteria to restrict the correlated response in body size and to potentially increase overall economic merit, especially when selecting for milk or protein yield.