IMPROVING FERTILITY DURING HEAT STRESS IN LACTATING DAIRY COWS

Heat stress is responsible for large declines in pregnancy rates of dairy cattle during hot months throughout most of the United States. Infertility caused by heat stress is a growing problem because of annual increases in milk yield that makes cows less able to regulate body temperature and because of global climate change. There is thus a compelling need to develop approaches for reducing the summer decline in fertility. It is also imperative that accurate information be developed regarding the economic returns from various strategies and that innovative extension approaches be developed that allow application of these strategies on individual dairy farms. Improving fertility during heat stress will improve Daughter Pregnancy Rate (DPR) and result in significant profit. On a national level, increasing DPR from 22% to 25% would result in an annual economic return of $552 million. The specific objectives of the proposal are to: 1) Evaluate physiological, nutritional, and genetic approaches to improving fertility in summer including a) embryo transfer using in vitro produced, vitrified embryos, b) provision of antioxidants to reduce effects of heat stress on the reproductive tract, immune system and embryonic function, c) feeding of niacin to enhance body temperature regulation, d) cooling in the dry period to cause long-term changes in milk yield and reproduction and e) identification of quantitative trait loci (QTL) for genetic selection for regulation of body temperature; 2) Develop software that a) evaluates the profitability of proposed investment decisions to alleviate the effects of heat stress at the farm level, b) optimizes breeding decisions for individual cows and c) is available online to dairy farmers and their advisors using DAIReXNET; 3) Engage in technology transfer regarding novel approaches for improving fertility to dairy farmers and dairy farm personnel in English and Spanish using DAIReXNET and extension road shows; and 4) Assess changes in producer behavior and seasonality of animal performance over time in response to the research and extension program using producer focus groups and data collected from individual dairies and DHIA. The main outcome of the project will be to provide the dairy farmer with new tools for reducing effects of heat stress on reproduction (Objective 1) and for evaluating investment decisions and optimizing breeding decisions to maximize profitability (Objective 2). In addition, completion of the project will result in dairy farmers and their employees who are educated about management procedures for reducing effects of heat stress (Objective 3) and tools and procedures will be in place for long-term evaluation of the effectiveness of the research and education program for changing dairy farm practice and profitability (Objective 4). Overall, the impact of the project will be increased dairy farm profitability and increased international competitiveness of the US dairy industry. The net result of achievement of these goals will be increased dairy profitability.