Integrating nutritional and reproductive models to improve reproductive efficiency in dairy cattle

Successful reproduction requires coordination among neural, endocrine and nutritional systems leading to ovulation, insemination and a uterine environment that allows embryonic growth and attachment. These processes are a function of genetics, dietary nutrient composition and intake, and housing and climate. We lack a systems biology approach to study and define the control of reproduction in the dairy cow. Pregnancy rates in the best managed herds only approach 25 to 30%, and may be due to the multifactorial nature of reproductive processes (McNamara, 2010). Lower fertility increases the cost for insemination because of low reproduction performance and remains a primary reason for culling cows in the first three weeks of lactation (Chagas et al., 2007). Additional days the cow is not pregnant beyond the optimal time post-calving are costly to the dairy producer. Low fertility has often been blamed on high rates of milk production, but this is not the only factor affecting reproduction (Sangsritavong et al., 2002). There are three major systems of reproduction that can be affected by genetics, nutrition and management: the hypothalamic-pituitary axis controlling initialization of cycling, the follicular development in the ovary leading to ovulation; and the successful fertilization and growth of an embryo in the uterine environment. Thus, the goal is to improve reproduction efficiency while decreasing any environmental impacts. Better nutritional management, genetic selection for fertility, and more attention to success can improve reproductive efficiency. In order to do all this efficiently, biosystems models can be of great efficacy.