Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 4/12/2002
Publication Date: N/A
Technical Abstract: Dairy Herd Improvement data from 3,604,990 Holstein and 264,775 Jersey lactations were used to assess variation in 70-d nonreturn to first service, days open, days to first service, calving interval, and number of services. Data were first inseminations from 1995 through 2000. Mean nonreturn rate was calculated by herd-year, and herd-years with nonreturn rates >90% were excluded. Nonreturn rate was not examined for cows that left the herd within 70 d. Mean nonreturn rate was 55.0% for Holsteins and 57.3% for Jerseys; mean number of services was 2.10 and 1.99. Factors evaluated were lactation stage at first service, parity, and partial regressions on peak yields for milk, fat, and protein and on age within parity. The least-squares model absorbed herd-year-month of first service. Lactation stage was evaluated only for nonreturn rate and number of services. Nonreturn rate was lowest for services before 50 d for both breeds and highest for services after 139 d for Holsteins and between 120 and 129 d for Jerseys. For all five traits and both breeds, fertility was highest for third parity. Fertility was lowest for both breeds for parities after fifth as measured by nonreturn rate and number of services and for first parity as measured by days to first service and calving interval. However. days open were greatest for first parity for Holsteins and for parities after fifth for Jerseys. Partial regressions of fertility on peak yield were generally significant (P < 0.01) for all breed-trait combinations. Fertility generally declined as peak milk and fat yields increased. Fertility was markedly lower for breedings <50 d after calving for Jerseys and <90 d after calving for Holsteins. For Jerseys, first service occurred later in first parity than in subsequent parities.