PA-PG-PL system in dairy animals and its significance: A review

Abstract

Animal husbandry plays an important role in strengthening the rural economy. Heat is a major constraint on animal productivity in the tropical belt and arid areas. Heat stress in dairy cows as all temperature-related forces encourage changes or adjustments which may occur from the cellular to the total animal level to help the cows stay away from physiological disorders and then to better adapt to an adverse thermal environment. Milk production is impaired as a result of the drastic changes in biological functions under heat stress. Activation of the hypothalamus-pituitary-adrenocortical axis by external stress liberates cortisol into blood plasma, which in turn induces the liberation of Plasminogen Activator (PA) from the mammary epithelial cells, where it activates the Plasminogen-Plasmin (PG-PL) system. Thus, this PA-PG-PL system is a milk-borne factor which down regulates the milk secretion during the summer stress. This negative feedback system specifically forms β-casein (CN) fragment (f) (1-28) from β-CN, which acts as the negative control signal of mammary gland. Based on these findings, casein hydrolyzate preparation is developed to reduce suffering from mammary gland engorgement associated with abrupt cessation of milking and to treat common clinical and subclinical infections of udder in dairy cows.