Effect of Increased Levels of Ovarian Hormones and Duration of Treatment on the Experimental Induction of Growth of the Cow's Udder

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Abstract
Mammary gland growth was induced experimentally by daily injection of 200 mg of progesterone with 200 ug of estradiol benzoate or by the feeding of 20 mg of diethyl-stilbestrol daily for periods of 60, 120, and 180 days to 20 heifers and one steer. Lactation was then initiated by daily injections of 0.3 mg of estradiol benzoate per 100 lb. body weight for 14 days. Treatment for 180 and 120 days apparently did not stimulate any greater mammary gland growth than 100 mg of progesterone and 100 ug of estradiol benzoate injected daily for 180 days, used in previous studies. The average maximum daily milk yields for the 16 animals on the lower level of hormones was 22.7 lb. per day, compared with the maximum daily milk yield of 23.8 and 21.2 lb. for the 14 animals treated for 180 and 120 days, respectively, with the higher level of estrogen and progesterone. The mean maximum daily milk yield for the 6 heifers injected for 60 days was 10.2 lb. Average maximum daily milk yield for the 3 lowest producers was 3.9 lb., compared with 21.4 lb. per day for the 3 highest producers of this group. Twenty milligrams of diethyl-stilbestrol administered orally proved equally as effective as 200 ug of estradiol benzoate injected subcutaneously in synergizing with 200 mg of progesterone injected daily to stimulate mammary gland development. When the lactation curve of the experimental heifers began to decline after reaching their maximum milk yield, either estradiol benzoate at the level used to initiate lactation or the feeding of diethyl-stilbestrol at levels of 30 and 40 mg/day/100 lb. body weight was administered for 7 days. During the week of administration, milk yield declined slightly. This was followed by a variable increase in milk yield for several weeks, reaching peaks of lactation, in some cases, above the initial maximum production.