Authors: MEHMET ŞÜKRÜ GÜLAY, FATMA ŞEFİKA HATİPOĞLU
Abstract: The major objectives of an efficient dairy farm operation include a successful lactation period, high milk yield relative to the feed costs, reproductive competence, and finally the returning of the cow to the body condition score (BCS) that existed before lactation so she will be prepared for another lactation. In cows a milk yield response to bovine somatotropin (bST) treatments at 60 d after parturition has been well studied and fully documented. Milk production response to bST occurs because of its known effects on partitioning of nutrients and because a greater proportion of the nutrient intake is used for milk synthesis. It increases liver glucose output, cardiac output, blood flow to the mammary gland and uptake of nutrients used for milk synthesis by the mammary gland among other effects. In addition, ST decreases the rate of oxidation of amino acid and glucose and therefore decreases glucose clearance. Treatment with bST results in coordinated changes of various organs and tissues that naturally occur during the transition from a nonlactating to lactating state when circulating concentration of ST is high. Because of the known effects of bST described above, use of bST during the transition period may cause positive and beneficial effects supporting milk synthesis prior to parturition. This review recaps the diverse physiological effects of ST on lactation, discusses the major mechanisms that mediate these effects, and summarizes the recent studies using bST during the transition period to increase milk production in cows.
Keywords: Somatotropin, lactation, transition period, metabolism, dairy cow.
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