THE ACROSS-BREED EVALUATION OF DAIRY CATTLE IN NEW ZEALAND

New Zealand dairy cattle are genetically evaluated using an across-breed animal model fitted to production records every three weeks. The traits evaluated and included in economic indices are milk volume, fat and protein yields, lactating cow liveweight and survival. Some additional traits (e.g., animal and udder conformation) are evaluated but not included in any economic index. This evaluation system, which replaced the previous systems as from June 1996, incorporates three major research findings. First, a new methodology to predict otal lactation yields from individual test-day information. This accounts for any number of herd tests over any testing frequency and allows for variable information among herdmates and for the effects of culling. Second, a mixed model routine to calculate breeding values using a single trait repeatability model equation, allowing for heterogeneous subclass variation and including fixed breed and group effects. Third, an economic model to derive relative economic values parameterised to a fured feed supply. Economic indexes describe animal profitability per unit of feed and account for the variation in body size and individual productivity that is a feature of across-breed evaluation. A programme of industry consultation was integral to these developments over some five years, in tandem with an educational campaign targeted at all 14,500 farmers plus other industry players