Changes in First Lactation Dairy Herd Improvement Records

Abstract

Dairy Herd Improvement Association records for all first lactation Holstein and Jersey cows from Pennsylvania were analyzed for DHIA production years 1985 to 1990. A total of 504,411 Holstein and 15,847 Jersey records were used. Average age at first calving across all years was 26.64 mo for Holsteins and 25.36 mo for Jerseys. During the 6-yr period, age at first calving decreased .6 and .3 mo for Holsteins and Jerseys, respectively. Actual first lactation milk production and milk fat and milk protein yields increased by 661, 20, and 6kg and 418, 19, and 7kg for Holsteins and Jerseys, respectively. Average BW at first calving did not change during the 6-yr period for either breed. The distribution of age at first calving was skewed toward older calving ages for both breeds. The decrease in average age at first calving resulted in a greater percentage of the population calving at 24 mo of age in later years. In most cases, the difference in 305-d milk production by Holsteins calving for the first time at 24 versus 30 mo was less than 100kg. Jerseys showed no advantage in 305-d milk production by calving later than 22 mo.