REGULATION OF CELLULAR APOPTOSIS AND SURVIVAL IN THE BOVINE MAMMARY GLAND

Sustainability of our dairy production systems requires that dairy farmers continue to improve productive efficiency of their operations, resulting in an economically viable system where a high quality food product is affordable for the consumer and profitable for the farmer. In addition, a new broader definition of sustainability includes a requirement to minimize negative environmental impacts of the industry. Productive efficiency can be defined as the milk output per unit of input (e.g. feed, labor, veterinary costs, etc.). Since feed represents the major cost of producing milk, productive efficiency of a dairy cow may be calculated in terms of the ratio of milk yield to nutrient costs. Maintenance requirements for dietary energy and protein are constant regardless of the level of milk production. As milk production increases, a greater proportion of total nutrient intake is used to synthesize milk. In other words, maintenance costs are diluted, and more milk can be produced from fewer cows. Producing more milk from fewer resources has substantial environmental benefits as well. Animal waste products are reduced, as is soil erosion and the use of fertilizer, water and fossil fuels associated with dairy farming. Peak milk production in dairy cows occurs six to eight weeks after calving. After this, milk yield gradually decreases. In dairy cows, the decline in milk yield following peak lactation is associated with loss of the milk-secreting cells of the gland through a programmed cell death pathway termed apoptosis. The cellular and molecular mechanisms that induce apoptosis following peak lactation are unknown. The goals of this proposal are to understand the complex processes inside the milk-secreting cell that lead to cell death, and how survival factors that oppose cell death counteract these mechanisms. Cellular and molecular biology approches will be used to identify the key proteins in these pathways and the regulatory mechanisms that control their action. Conducting these experiments will train the next generation of scientists in the use of recently developed molecular and cellular technologies, leading to advancement of our knowledge of molecular regulation of milk production. Technological advances in the biological sciences will make it possible in the future to target the key pathways that regulate milk yield and persistency in dairy cows. However, targeted approaches will require understanding the basic underlying biology that regulates mammary gland development and lactation. Overall, understanding the mechanisms that allow the milk-secreting cells in the gland to divide, become functional cells, and survive, is fundamental to future technological gains in terms of productive efficiency.