INSULIN-LIKE GROWTH FACTORS AND THEIR BINDING PROTEINS IN THE BOVINE MAMMARY GLAND

Milk production is dependent on the number of milk-producing cells in the mammary gland at any one time. Milk production increases following calving in a dairy cow, reaching a peak after 6 to 8 weeks, after which milk yield gradually declines. At a certain point the cow is not producing enough milk to pay for feed, housing and labor costs. Therefore, farmers rebreed cows early in lactation so that they will calve again in a defined interval, thus reinitiating the lactation cycle. The decline in daily milk yield in the later half of the lactation cycle is thought to be due to the gradual loss of milk-producing cells through the process of apoptosis. However, little is known regarding how this process is regulated by local factors at the tissue level. The present studies will use molecular techniques to determine the role specific factors play in regulating cell number by affecting either cell division or cell death. Using cultured cells, gene knock-down technologies will be used to determine if growth-stimulatory or inhibitory factors are able to exert their effects if specific molecules are missing from the mammary epithelial cell (i.e. the milk producing cells). A better understanding of this process will lead to new technologies that will enable the persistency of milk production to be sustained by decreasing the loss of milk-producing cells. This will allow cows to produce milk at a higher level longer, without having to be rebred. The ability to make more milk from fewer cows will decrease animal waste products, soil erosion, and the use of fertilizer, water and fossil fuels associated with dairy farming. Such reductions are important for the sustainability of dairy farming in the US.