Components of the Relationship Between Level of Production and Rate of Maturity in Dairy Cattle

Abstract

It is important in selection programs to arrange for the optimum combination of selection pressure and size of the generation interval to obtain the maximum rate of improvement (2, 5, 10). In the selection of dairy sires, genetic rate of progress can be increased by using only first lactations of daughters because of the decreased age of sires when progeny tests become available (11). However, sires might be ranked differently if more than first lactation records are considered. To determine whether first lactation production is influenced by differences in rate of maturity is the object of this study. Lush (6) and Spalding (13) have shown discrepancies between different sets of age correction factors. This indicates that environmental factors affect the shape of the age curve. Johansson (5) states that increase in production with age decreases with increased level of feeding and management. Genetic information on the relationship between age and level of production has not heretofore been available.