Effects of Early and Late Breeding of Heifers on Multiple Lactation Performance of Dairy Cows

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Abstract
Dairy heifers were randomly divided into two treatment groups. One group of 253 heifers was bred at first estrus after 350 d of age and the second group of 249 heifers after reaching 462 d of age. Feeding and management practices were identical; groups differed only in age at first breeding. This report compares production of second and third lactations, reproductive traits observed during first and second lactations, and lifetime performance. Comparisons of heifer reproduction and first lactation production were reported earlier. Although the 462-d breeding age group of heifers had slighlty better first lactation performances than the 350-d breeding age group, these advantages were not carried over to second and third lactations. No significant differences existed in three-parity performance between the two breeding groups. The 350-d breeding group had longer 61-mo productive life (730 vs. 623 d), produced greater 61-mo total milk (10,693 vs. 9218 kg), and yielded more milk per day of 61-mo herdlife (6.8 vs. 5.9 kg). A reduction of 1 mo in age at first calving would increase three-parity and 61-mo total milk by 427 and 554 kg, respectively. Results from this study suggest that early breeding is a viable and practical approach to improve profitability for the dairy industry.