Dairy and Limits to Production 434 EXPERIENCES FROM BREEDING FOR ECONOMIC EFFICIENCY IN DAIRY CATTLE IN NEW ZEALAND

New Zealand dairy farmers use a number of performance indicators to describe their systems. Most of the performance indicators are scaled to a unit of feed or a proxy that relates a cow to a unit of feed, such as stocking rate or kilograms of live weight per tonne of feed. Genetic improvement of dairy cows can contribute to increasing the net income per unit of feed consumed. The current economic index for dairy cattle selection is the breeding worth (BW) which has units $/4.5t of dry matter (DM). The BW index includes metabolisable energy requirements calculated for milk production, maintenance, pregnancy, live weight loss and gain, and the rearing of replacements. Data from the national genetic evaluation system was used to examine the progress in selection for economic efficiency over the last 20 years. The first 10 years represented selection prior to BW. The genetic trend for milk solids yield has increased and the genetic trend for liveweight, while remaining positive, has decreased since the introduction of BW. Prior to the introduction of BW an extra kilogram of milk solids genetic gain was accompanied by an extra kilogram of genetic gain for liveweight. The change in the average milk production yield and liveweight over the last 10 years indicates that the average feed intake has increased by 9% and the partitioning of dry matter to milk production relative to maintenance has increased from 56% to 59%. Over the same period the genetic trend for body condition score (BCS) is essentially 0 BCS units/year. There is no evidence for increased body catabolism over this period, which is important because increasing biological efficiency with increasing body catabolism could result in fertility and health problems. Five key factors have been responsible for the success and high adoption rate of the breeding worth index. These factors are: the use of farm trials; the ability to compare all animals regardless of breed or breed cross; providing farmers with BW and production worth indexes for their cows; and improving the economic index to include the major components of profitability; an effective extension strategy. The future may require the BW to accommodate residual feed intake (RFI) and national genetic evaluation centres will need to consider how or if they integrate genomic selection breeding values in their systems.