The objective of this research was to identify major determinants of net profit per cow. Data were from the Dexcel strain trial over three seasons, in which Holstein-Friesian cows were managed in groups of 12 to 20 cows in eleven farmlets. Milk returns were calculated from lactation yields of milk, fat and protein. Net profit per cow was calculated as the net return from milk sales plus sales of calves minus feed, fertility, health, shed and working expense costs. Annualised present values were derived using asset replacement theory and discounting to account for different numbers of years of data according to the year in which an animal entered the herd. Net replacement costs and average replacement returns were included where animals were replaced before the end of the trial. Partition analysis was used to identify indicators of cow profitability. Partition analysis recursively sub-divides data creating a tree of partitions. Each split is chosen to maximise the difference in profitability between branches of the split. Variables on which data could be partitioned included breeding values, Breeding Worth and traits measured in first parity. The key determinants of profitability were lactation yield of protein and fat, percentage of fat and Breeding Worth. When these variables were fitted to a multiple regression model where the response was annualised present value, the adjusted R2 was 52%. KEYWORDS: asset replacement model; economics; dairy cattle.
Proceedings of the New Zealand Society of Animal Production, Volume 65, Christchurch, 68-73, 2005
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