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Effect of Age and Norgestomet on Endocrine Parameters and Production of Embryos in Superovulated Beef Cows^1,2,3,

West Virginia University, Morgantown 26506-6302 and Select Embryos, Inc., Plain City, OH 43064

Abstract

Effects of age of cow and a norgestomet (N) implant on number of embryos and endocrine responses to induction of superovulation were studied in old (> 12 yr) and young (5 to 7 yr) lactating beef cows. Seventeen cows (8 old and 9 young) received a 6-mg N ear implant on d 4 or 5 of the cycle (d 0 = estrus); the remaining 17 cows (9 old and 8 young) served as untreated controls (C). All animals were treated with 38 mg of porcine follicle-stimulating hormone (FSH-P) in decreasing dosages over a 4.5-d period beginning on d 10 or 11. Regression of the corpus luteum was induced with injections of PGF₂ at 0800 and 2000 on d 4 of FSH-P treatment; implants were removed at the second injection of PGF₂. Cows were inseminated artificially 12 and 24 h after onset of estrus. Embryos were collected on d 7 or 8 postinsemination. Blood samples were obtained daily at 0800 from 2 d prior to initiation of treatment with FSH-P until collection of embryos. An additional sample was collected each day at 2000, from the first injection of PGF₂. to 1 d after onset of estrus. Samples were assayed for luteinizing hormone (LH), progesterone (P₄), follicle stimulating hormone (FSH) and estradiol-17ß (E₂). Total number of embryos plus ova recovered was lower (P < .01) in N-treated (5.2 ± 1.1) than in C-treated (10.6 ± 1.6) cows. No differences were seen for this variable between young and old cows. Mean numbers (± SE) of degenerating embryos were 2.5 ± .9 for young C, 0 for young N-treated, .6 ± .4 for old C and 2.2 ± 1.0 for old N-treated cows (treatment x age, P < .05). Old cows had higher (P < .05) FSH prior to initiation of treatment with FSH-P (.92 ± .04 vs. .80 ± .05 ng/ml). They also had higher (P < .05) preovulatory E₂ (38.1 ± 3.1 vs. 31.2 ± 2.3 pg/ml) and LH (26.1 ±6.1 vs. 8.7 ± 1.7 ng/ml) than young cows. The differences in concentrations of FSH and E₂ in young and old cows may help explain effects of age of cow on production of embryos in response to superovulatory treatments.

¹ Published with the approval of the Director of the West Virginia Agric. and Forestry Exp. Sta. as Scientific Paper No. 2083.

² Supported by a grant from Select Sires, Inc., and by Hatch Project 224. The authors gratefully acknowledge G. D. Niswender, Colorado State Univ., for antiserum to luteinizing hormone (LH); L. E. Reichert, Jr., Albany Medical College, for purified LH; Natl. Inst. of Diabetes, Digestive and Kidney Diseases and the National Hormone and Pituitary Program for immune-reagents for the follicle-stimulating radioimmunoassay; E. Henderson, CEVA Laboratories, for norgestomet implants; John Chenault, The Upjohn Co., for prostaglandin F₂; E. C. Townsend for assistance with statistical analyses; and Diana Kirkpatrick-Keller for assays of steroids.

³ Presented in part at the 78th Annu. Mtg. of the Am. Soc. of Anim. Sci., Manhattan, KS, Abstr. 459.

⁴ Div. of Anim. and Vet. Sci.

⁵ Present Address: Centro de Ganaderia, Colegio de Postgraduados, Chapingo, Mexico 56230.

⁶ Select Embryos, Inc.

⁷ Dept. of Obstet. and Gynecol.

⁸ To whom reprint requests should be addressed.