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

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Abstract
Heritabilities of the 1st, 2nd, and 3rd lactations were compared, using 312 dam-daughter pairs from the Iowa State University herd and 472 dam-daughter pairs from Iowa DHIA data. The trends observed suggest (but do not demonstrate unmistakably) that the 1st record indicates the breeding value of a cow slightly more accurately than the 2nd or 3rd records do. Second and 3rd records of a sires daughters do not add much information to his proof but 2nd and 3rd records do help considerably in estimating the breeding value of a cow. In averaging these it is possible (but not certain) that the 1st records should receive somewhat more weight than the 2nd or 3rd. Questions which seem important in their bearing on this problem but which seem still unanswered are whether terminal records should be treated differently from non-terminal records and the possible effects of the inevitable selection among the daughters when only those with 2 or more records are studied.