ASAS/ADSA Breeding and Genetics: Genetics Evaluation and G-E Interactions: Dairy Cattle

The objective of this study was to describe the production systems in countries that participate in international dairy sire evaluations, and to identify factors that cause variation in progeny performance between herds. Test day data from first lactation Holstein cows in Australia, Austria, Belgium, Canada, Czech, Estonia, Finland, Germany, Hungary, Ireland, Israel, Italy, the Netherlands, New Zealand, South Africa, Switzerland, and USA were used. These data included 233,673 herds, 16,403,413 cows, and 131,907,373 test day records from cows calving between 1/1/90 and 12/31/97. Herds were grouped into 5 quintiles for each of 11 management variables and 2 climate variables. Heritability of milk yield was calculated within each quintile of each variable, and genetic correlations between quintiles were computed. Genetic correlations less than unity and significant differences in heritability between quintiles were found for peak yield, average sire PTA milk, temperature, fat to protein ratio, days to peak yield, within-herd standard deviation of milk yield, and percent North American Holstein genes. Currently, differences in production systems between countries are considered in international sire evaluations. However, variation in management or climate within countries is ignored. We have identified some of the factors that cause genotype by environment interactions between individual herds. This research shows that it is more reasonable to define traits based on the production conditions in each herd, as opposed to defining traits based on country borders. Grouping herds on these variables should create international sire evaluations that are more appropriate for genetic selection decisions on individual farms, because each sire will receive a PTA for each unique production system. In addition, the number of unique production systems will likely be less than the number of countries, and this will lead to greater accuracy of parameter estimates and a more efficient international evaluation system.