Use of Later Records in Dairy Sire Evaluation: A Review

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Abstract
Performance in first lactation has been the standard of evaluation for most genetic studies with dairy cattle. First records are available sooner on more cows and are less susceptible to error from selection, injury, previous days dry, and mastitis than are later records. However, first records have been considerably less than perfect in predicting traits of lifetime performance, which should be the primary selection objective in dairy cattle. Later records provide additional information for more accurate sire evaluations and should be a better index of health and resistance to mastitis than first lactations. The economic importance of later records relative to first is that there are more and actual yields are higher. Herds with more older cows can reduce commitment of resources to heifer rearing, and heifers can be selected more intensely prior to first calving than herds with more cows of younger ages. Some sire evaluation systems ignore later records because of computational expense, potential selection bias, and difficulty of age adjustment. Later records may contain useful information relative to lifetime profitability of sire progeny groups. Development of proper methodology for utilizing information available in later records appears fruitful for research.