Characterization of biological types of cattle: indicator traits offertility in beef cows

Genetic diversity among breeds of cattle allows producers to select animals for specific environments or market conditions. Reproductive efficiency is a multi-component trait that is largely influenced by environmental influences such as health and nutritional status; however, there are clearly genetic components to reproductive efficiency, and breed differences in a number of indicator traits associated with fertility and cow productivity have been identified. Historical indicators of fertility include scrotal circumference, age at puberty, and postpartum interval. Both age at puberty and postpartum interval are laborious traits to collect in heifers and cows because they require many days of detection of behavioral estrus. In recent years, the addition of ultrasonography to management practices has allowed for the collection of female traits such as follicle diameter, antral follicle counts, and fetal age that are not as labor intensive. These additional diagnostic traits provide novel phenotypes for the identification of genetic markers of fertility and cow productivity, which would be the ultimate goal. Genetic markers of the number of follicles in the bovine ovary have the potential to identify heifers that will be highly productive cows. Furthermore, identifying and understanding the genes that control various reproductive traits and the response to stressors, such as temperature and nutrient availability, could improve production efficiency by improving management and breeding decisions in a wide range of production environments.