Remodeling of mammary tissue and lactation persistency / Remodelage de la glande mammaire et persistance de la lactation

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The long range objectives of this research program are to improve our knowledge of the biological process involved in the control of mammary gland involution and to develop economically viable and consumer acceptable technologies or practices that would improve lactation persistency and enable longer lactation in dairy cows. Extended lactation would reduce the proportion of cow's lifetime spent in early lactation and, thus, the occurrence of disease, metabolic disorder and reproduction failure associated with this period. Apoptosis occurs in late lactation and accounts for the progressive loss of secretory cells in declining lactation. Therefore, there are considerable incentives to identify the factors which regulate mammary apoptosis. Recent work carried out in my laboratory, have shown that the hormone prolactin (PRL) is galactopoietic in dairy ruminants and a survival factor for mammary cells. Therefore, it is possible that PRL, especially the milking-induced PRL, is an important factor for lactation persistency by limiting the loss of cells and maintaining cell differentiation. We also found that the galactopoietic action of PRL is modulated at the level of the mammary gland. My hypotheses are: -It is possible to reduce the rate of decline in milk production by reducing the rate of mammary cell death; the milking-induce PRL release is important for the differentiation and the survival of the mammary cells and; several factors affect milk production and lactation persistency by modifying gland sensitivity to PRL. The short range objectives are: 1- To determine the factors controlling the milking-induced release of PRL. 2- To determine how sensitivity of the mammary gland to PRL is modulated. 3- To determine if factors that affects milk production affects also PRL secretion and/or sensitivity. 4- To determine the effect of the dry period on the mammary gland.