Source of Progesterone Prior to Puberty in Beef Heifers1

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Abstract
The pattern of concentrations of progesterone in plasma was characterized by two transient increases prior to puberty. The source of these increases of progesterone was studied in beef heifers. Basal concentrations of progesterone (ng/ml; x̄ ± SE) averaged .7 ± .1 in all heifers. Progesterone increased to 2 ± .2 during the first elevation, the duration of which was 7 ± 2 days, then decreased to .9 ± .2 for 4 ± 1 days after which it increased again to 2 ± .2. Twenty-four to 30 hr after progesterone had increased in two consecutive samples during the first (four heifers) and second (four heifers) elevations, ovariectomy was performed via a supravaginal incision and the ovaries were examined grossly and histologically for the presence of luteal tissue. Seven heifers which had not shown increases in progesterone were ovariectomized as controls. After ovariectomy, concentrations of progesterone in plasma from heifers that had shown a prior increase returned immediately to concentrations seen in those that had not shown any increase (.6 ± .2 ng/ml). Neither the first nor the second elevation of progesterone was accompanied by the formation of a palpable corpus luteum or grossly visible luteal structure on the ovaries. Ovaries were examined histologically in 10 sections of 12 µm each, taken at 1,800 µm intervals. Microscopic examination revealed the presence of compact luteal tissue in three of four heifers that had exhibited the first increase and in three of four heifers that had exhibited the second increase of progesterone in plasma. The approximate diameters of these luteal tissues observed ranged from 1.5 to 6 millimeters. It is concluded that the first increase of progesterone prior to puberty was produced by luteal tissue embedded within the ovary, but not palpable or observable grossly on the ovarian surface. The second increase probably originated in a similar manner within the ovary. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.

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