Reliability of First, Second, and Third Records for Estimating the Breeding Value of Dairy Cows

Abstract

Summary Heritabilities of the first, second, and third lactations were compared, using 312 dam-daughter pairs from the Iowa State University herd and 472 dam-daughter pairs from Iowa DHIA data. The trend observed in these data, as well as the results found in the literature, suggest (but do not demonstrate unmistakably) that the first record gives a somewhat more accurate estimate of the breeding value of a cow than the second or third. Using the first seems adequate for proving sires, but the information in the second and third records would help considerably in estimating the breeding values of cows. For optimum use for this purpose, perhaps less weight should be given to the second and third record than to the first. The fact that the second and third records are affected by sources of variabilities, as dry period, which are not present in the first may account for part of the difference in heritabilities. The effect of terminal records and of the selection of the cows, when only those with two or more records are studied, may also have some bearing on the apparent differences in heritability among the first, second, and third records, but these points need further investigation.