Submitted to: Hoard's Dairyman
Publication Type: Popular Publication
Publication Acceptance Date: 3/10/2003
Publication Date: N/A
Technical Abstract: Milk production has nearly doubled over the past 40 years, while days open has increased by about 40 days. Although cow fertility has been selected for indirectly via genetic evaluations for productive life, direct selection has been hampered by low heritability of fertility traits (about 4%) and lack of genetic evaluations for those traits. The most reliable data source for cow fertility evaluations is days open as reported through Dairy Herd Improvement milk recording plans and as verified by subsequent calving date. For cows without verified days open, 280 days (a typical gestation length) is subtracted from calving date to calculate days open in previous lactation. For cows that are culled for infertility, a value of 250 days open is assigned. Daughter pregnancy rate is the amount by which daughters of a particular sire are expected to exceed or to fall short of a herd's average 21-day pregnancy rate. A 1% increase in daughter pregnancy rate corresponds to a decrease of 4 days open. Daughter pregnancy rate encompasses a cow's ability to return to normal reproductive status after calving, to display visible signs of estrus, to conceive when inseminated, and to maintain pregnancy. Genetic evaluations for daughter pregnancy rate were developed based on the same animal model system used for milk, type, and other traits and adjustments for known environmental factors such as contemporary group and age of cow. Daughters of the best fertility bulls will have pregnancy rates 2 to 3% higher than other cows in a herd, whereas the poorest fertility bulls will sire daughters that fall 2 to 3% below average. When expressed as days open, differences between the best and worst fertility bulls span about 3 weeks. The first official national genetic evaluations for daughter pregnancy rate will be released in February 2003 and will assist dairy producers in maintaining and improving cow fertility.