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Corpus Luteum Function Following Spontaneous or Prostaglandin-Induced Estrus in Brahman Cows and Heifers^1,2,3,4,

Texas A&M University, College Station 77843 and North Carolina Agricultural and Technical State University, Greensboro 27411

Abstract

Corpus luteum (CL) function following spontaneous or prostaglandin F₂-induced estrus was studied in 27 Brahman cows and 16 Brahman heifers. Females received one injection of 0, .38, .75 or 2.25 mg alfaprostol® (PGF)/100 kg body weight at 12 ± .1 d post-estrus. Serum progesterone (P₄) during CL formation, following the subsequent estrus, increased over time (P<.001, 1 to 13 d post-estrus) and was influenced by PGF (P<.06) and a PGF x time interaction (P<.02). Low serum P₄ concentrations were observed during CL formation (d 3, 4, 10, and 12) in cattle that received 2.25 mg PGF. On d 13 post-estrus, CL were removed. No differences in weight, P₄ content or number of luteinizing hormone (LH) receptors was evident between CL derived 13 d following spontaneous vs PGF-induced estrus. The CL formed following PGF-induced estrus had fewer large (P<.002) and small (P<.09) luteal cells in heifers, a lower (P<.008) percentage composition of histological type I and II luteal cells in cows and a lower (P<.0001) in vitro P₄ response to LH in both cows and heifers when compared with the CL formed following spontaneous estrus. Cows had heavier (P<.002) CL with a higher (P<.05) number of large cells, a higher (P<.09) percentage composition of histological cell type I and II luteal cells, and a higher (P<.03) in vitro basal and stimulated P₄ secretion. It is concluded that 1) the events associated with artificially shortening the estrous cycle with PGF altered subsequent CL function in Brahman females; 2) cows had heavier CL, which were composed of more steroidogenically functional luteal cells, than heifers and 3) age of animal interacted with PGF to alter subsequent CL function in Brahman females.

¹ Journal paper TA 22061, Texas Agr. Exp. Sta.

² This study was a contribution of Western Regional Project W-112, Reproductive Performance in Domestic Ruminants.

³ This work was supported in part by a grant from Hoffmann-LaRoche, Inc., Nutley, NJ.

⁴ Appreciation is extended to Dr. Terry Nett and Mr. Tim Braden, Dept. of Physiol. and Biophys., Colorado State University, Fort Collins, for help in development of the LH receptor assay.

⁵ Texas A&M Univ. Agr. Res. and Ext. Center, Overton 75684.

⁶ Dept. of Anim. Sci., North Carolina Agr. and Tech. State Univ., Greensboro 27411.

⁷ Present address: Anim. Breed. Sec., Beef Cattle and Sheep Branch, Alberta Dept. of Agr., 7000-113th St., Edmonton, Alberta TGH 5T6.

⁸ Dept of Anim. Sci., Texas A&M Univ., College Station 77843.