A Comparison of Dairy Sire Progeny Tests Made at Special Danish Testing Stations with Tests Made in Farmer Herds

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Abstract
The data for this study con-sisted of the 1st lactation milk and butterfat records of 5454 daughters of 305 Red Danish Milkrace sires tested at the Danish bull testing stations and the 1st test year milk and fat records of 3270 daughters of 110 of these same sires tested in farmer herds. Heritabilities were estimated on a within station year basis for the test station data. The field data were analyzed in 2 ways, after removing the differences between herds and after expressing each record as a deviation from its contemporary herd average. The heritabilities resulting from the 3 methods, assuming that the sire component is wholly genetic are 0.66, 0.29, and 0.23 for milk and 0.61, 0.27, and 0.22 for butterfat, respectively. It is concluded that the estimates based on test station data are higher mainly because environmental differences at the same test station in the same year are confounded with progeny groups thus putting much environmental variance in the sire components and increasing them more than the within-sire components. Estimates'' of genetic correlation between station tests and field tests were 0.68 for milk and 0.75 for butterfat. On the other hand, genetic correlations between independent field tests were 0.94 and 0.92 for mild and butterfat, respectively. In general, the field tests seem to be superior to station tests if the number of daughters per sire is 15 or more. This superiority increases as the number of daughters per sire increases. In areas where a high percentage of herds is on test there appears to be little need for special dairy sire progeny testing stations. To make the expected genetic gain from selection based on tests at special test stations higher than that now expected, more sires should be tested with fewer daughters per sire.