Updated index weights for the Australian Profit Ranking in dairy cattle

Several alternative selection indexes for dairy cattle are reviewed as possible replacements for the current version of Australia Profit Ranking (APR) including: an economically optimal solution (the economic index) and two alternative indexes where the relative emphasis on fertility and fitness (compared to protein) is increased. As survival is positively correlated to yields of milk, fat and protein (production), the economic index is close to the maximum response which could be achieved for survival. However, fertility is more difficult to improve because the correlation between fertility and production is negative. To achieve a significant increase in response for fertility, its weight would have to increase considerably. Arbitrary multiples of the economic weight for survival and fertility were considered to investigate the impact on responses to selection. The index weight on survival was doubled and fertility quadrupled in the fitness index and the weight on fertility was doubled in the fertility index. Compared to the economic index, the loss in economic response was $1.40 (6%) for the fitness index and $0.21 (1%) for the fertility index. In the economic index, 53% of the total response is due to improvements in production traits, 37% is due to improved survival and 5% is due to fertility, with the remaining 5% for cell count, liveweight, temperament and milking speed. In the fitness index, the proportion of response due to production traits is 44%, survival 41% and fertility 9%. An index with more emphasis on fitness traits may improve the uptake of the APR. If this occurred it would have a favourable effect on overall genetic improvement of Australian dairy cattle.