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Estrogen-Progesterone Requirements for Udder Development in Ovariectomized Heifers^1,2,

Department of Physiology and Department of Dairy, Michigan State University, East Lansing

ABSTRACT

The levels of progesterone (P) and estradiol-17ß (E) necessary for maximal udder development were studied in 30 ovariectomized 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 µg E or 100 mg P and 400 µg 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 hormone-induced mammary development.

¹ Published with the approval of the Director of the Michigan Agricultural Experiment Station as Journal Article no. 4162.

² We are indebted to Dr. Robert Zimbelman, The Upjohn Co., Kalamazoo, Michigan, for providing us with the castrate heifers and hormones used in this study.

³ United States Agency for International Development scholar.