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Test Interval Method of Calculating Dairy Herd Improvement Association Records

Department of Animal Science, North Carolina State University, Raleigh

ABSTRACT

Conclusions: The mean differences between the test interval records and the AE records for milk and fat yields and per cent fat were of the same magnitude as the corresponding mean differences between the centering date records and the AR records for the 744 lactations in this study. The mean differences between the AE (actual) records for milk yield and the centering date records, both monthly and bimonthly, were in general agreement with those reported from other studies. The mean differences for both the centering date records and the test interval records suggested that there are no important biases in either method of calculation. Within herd correlations between the centering date and the test interval records for milk and fat yields and per cent fat were 0.998 or 0.999 in all cases. The standard deviations of the percentage differences between the AR records and the centering date records were similar in size to the corresponding values for the test interval records and were in agreement with those from other published reports.

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