The Experimental Induction of Growth of the Cow's Udder and the Initiation of Milk Secretion

Abstract

An experiment is reported concerning the experimental induction of growth of the mammary glands of the cow''s udder followed by the experimental induction of milk secretion. The group of heifers included 6 Jerseys and 1 Holstein that had failed to conceive, 1 set of Jersey twins diagnosed as monozygotic, and 1 freemartin Guernsey. To induce lobule-alveolar mammary gland growth in these animals, they were injected daily with a mixture of 100 mg of progesterone and 100 jug of estradiol benzoate for a period of 180 days. During this period there were few external signs of change of the udder except slight length-ening of the teats and hyperemia of the skin. Estrous cycles were inhibited, and mounting and pelvic changes observed when extrogen alone is injected were not observed. To induce milk secretion, 3 mg of estradiol benzoate were injected daily for a period of 14 days or more. A marked increase in milk yield commenced from the 3rd to 6th days in the Jerseys but was delayed in the Holstein. The Guernsey freemartin failed to come into copious lactation. Maximum milk yields were reached 5-14 weeks after the beginning of stimulation. On the basis of various com-parisons, it was concluded that the maximum production of milk rather closely approached the milk production which might have been obtained had they calved normally. The failure of the Guernsey freemartin to respond to the treatment cannot be explained at this time. Although complete chemical analysis of the milk secreted by these heifers was not made, evidence for the normality of milk composition furnished by pairs of identical twins under similar experimental treatment indicates that the milk stimulated by this method would be normal.