Estrogen-Progesterone Requirements for Udder Development in Ovariectomized Heifers

The levels of progesterone (P) and estradiol-17fl (E) necessary for maximal udder development were studied in 30 ovarieetomized heifers.The two hormones were injected three times weekly for 20 weeks.Growth measurements were estimated from mammary weight, DNA, maximal volume, and histological rating; RNA and RNA/DNA values were also determined.The optimal combinations appeared to be either 200 mg P and 800 t~g E or 100 mg P and 400 ~g E. These doses produced tightly packed alveolar cells very similar to those of normally developed udders from five-month-pregnant heifers.None of the steroid combinations stimulated precocious milk secretion.A discrepancy between nucleic acid values and histological ratings of the udders was observed.It is suggested that several criteria be used to evaluate horumne-indueed mammary development.Numerous investigators have attempted to develop the udder and initiate lactation in dairy cows with hormone treatments.In most experiments estrogen alone, and a combination of estrogen and progesterone were administered (5).Treatment with these hormones has resulted in a great variability in milk yield, and a majority of animals produced less than normal quantities of milk.Additional studies indicated that treatment of heifers with diethylstilbestrol and progesterone, followed by an adrenal cortical hormone (9-fluoroprednisolone acetate, The Upjohn Co., Kalamazoo, Michigan), always initiated lactation, but the av-