An update of the National Breeding Objective for the New Zealand Dairy Industry

Abstract

The National Breeding Objective for dairy cattle in New Zealand expressed as a genetic selection index called Breeding Worth (BW), assesses sire and cow genetic merit now and sets the direction for the New Zealand cow of the future.  A major review of the calculations of the economic weightings that underpin the index has recently been undertaken. A modified approach to the costing of feed had only a modest impact on existing traits in the index, but opens up opportunities to calculate economic values for traits which shift feed requirements from one season to another. Such traits include autumn body condition score and lactation persistency.  A further major change to the index related to assumptions about the farmer response to shifts in herd genetic merit for survival. Historically, lower survival was assumed to result in lower voluntary culling, whereas the new model assumes that lower survival will lead to an increased requirement to breed replacement heifers. As a consequence, the economic values for residual survival, fertility, and to a lesser extent somatic cell score have increased substantially. These changes have been generally well received in the industry and have led to noticeable impacts on rankings of AI sires.