It would be useful if dairy farmers could have a tool to predict the lifetime performance of a cow, using the measured performance of the cow during early lactations. This would facilitate early decisions on culling and expected profitability. This was exactly what Dr M.M. Kelleher and colleagues in Ireland set out to investigate. Their results were published in the Journal of Dairy Science, Volume 98 of 2015, pages 4225–4239. The title of the paper was:Development of an index to rank dairy females on expected lifetime profit.
The objective of their study was to develop an index to rank cows on expected profit for the remainder of their lifetime, taking cognizance of genetic merit, permanent environmental effects and current status of the cow, including the most recent calving date and lactation number. From the results a so-called “cow own worth” (COW) index was established, intended to be used for culling the expected least profitable cows in a herd, as well as to inform purchase and pricing decisions for buying and selling cows.
The COW index consisted of the profit accruing from the current and future lactations, as well as the net replacement cost differential. The COW index was generated from estimated genetic and non-genetic values (sum of additive genetic merit, non-additive genetic merit and permanent environmental effects) of traits, their respective net margin values and transition probability matrices for month of calving, survival and somatic cell count; the transition matrices were to account for the predicted change in a cow’s state in the future. Transition matrices were generated from 3156109 lactation records from the Irish national database between the years 2010 and 2013. Actual performance records for 162981 cows in 2012 were used to validate the COW index. Genetic and permanent environmental effects were available for these cows from the 2011 national genetic evaluation system and used to calculate the COW index and their national breeding index values. The cows were stratified in low to high production groups within herd, based on their COW index value and national breeding index value.
The correlation between the individual animal COW index value and the national breeding index value at 0.65 was acceptable. Month of calving of the cow in her current lactation accounted for 18% of the variation in the COW index, whereas the lactation number of the cow accounted for an additional 3 percentage units. Cows ranking higher on the COW index yielded more milk and milk solids and calved earlier in the calving season than their lower ranking contemporaries. The difference in performance between the best and worst production groups was larger for cows ranked on the COW index than cows ranked on the national breeding index. It was concluded that the COW index developed should be useful to rank cows before culling or purchasing decisions on expected profit and it can be used as a complement to the Irish national breeding index, which identifies the most suitable females for breeding replacements.
Comment: The COW index appears to provide further value to genetic and economic value predictions and therefore something similar should be considered for the SA system.