Pharmacological acceleration of mammary gland involution in cows.

摘要

Mammary gland involution is a compound physiological process that is characterized by differentiation and apoptosis of mammary epithelial cells. Involution is controlled by prolactin, growth hormones, oestrogens, progesterone, cortisol and insulin-like growth factor 1 (IGF-1). Advanced pregnancy, infrequent milking, and mastitis increase epithelial cell apoptosis. Milk stasis triggers local stimuli which cause the leak-tight junctions and initiate involution. Cows are especially susceptible to intramammary infections (IMI) by contagious pathogens during the dry period and environmental pathogens during parturition. High milk yield during the dry period is a significant risk factor for the cows and udder quarters are usually infected with environmental pathogens during calving. It is observed that high producing cows rarely develop a keratin plug which is the natural protection against infection during dry period. Milk production has to be reduced in these high producing cows during the dry period either by restricted diet, interrupted milking or pharmacological treatment. It is also noted that intramammary infusion of colchicine and endotoxin during dry period accelerates mammary involution. Infusion of ConA or PHA near the dry period also accelerates mammary involution resulting in elevated levels of natural protective factors. Interleukin-2 accelerates involution and stimulates local antibody production more than pokeweed mitogen and LPS. Intramammary infusion of either rboGm-CSF or rboII-1 beta at the cessation of milking immediately increases the number of phagocytic cells in the mammary glands. These cytokines, particularly rboII-1 beta , can increase the rate of mammary gland involution. The infusion of beta 1.3-glucan during the dry period accelerates the involution process by increasing the somatic cells, particularly the number of macrophages in the milk. Casein hydrolysates are among the milk-borne factors that cause the disruption of tight junction integrity and induce involution in cows. Mammary tissue involution is affected by exogenous oestrogen through the activation of plasminogen. Endogenous oestrogen secreted by the developing fetus and placenta may partially mediate the gradual involution that occurs during lactation..