Estrogen-Progesterone Requirements for Udder Development in Ovariectomized Heifers

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Abstract
The levels of progesterone (P) and estradiol-17 B (E) necessary for maximal udder development were studied in 30 ovari-ectomized heifers. The 2 hormones were injected 3 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[mu] g E or 100 mg P and 400[mu] g E. These doses produced tightly packed aveolar cells very similar to those of normally developed udders from 5-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 hormone-induced mammary development.