Are corpora lutea induced by human chorionic gonadotropin (hCG) given on day 7 of the bovine estrous cycle functional?

Theriogenology41:293, 1994 A R E C O R P O R A L U T E A I N D U C E D BY H U M A N C H O R I O N I C G O N A D O T R O P I N (hCG) G I V E N O N DAY 7 OF T H E B O V I N E ESTROUS CYCLE FUNCTIONAL? PC SianangamaI, R. Rajamahendran I and C. Harvey-Clarld, ~Dept. of Animal Science, and 2Animal Care Centre, U.B.C., Vancouver, BC, Canada V6T 1Z4. The transfer of embryos into both uterine horns or the horn ipsilateral to the corpus luteum (CL)-bearing ovary has not consistently resulted in acceptable pregnancy rates (Christie et al., 1979 I. Reprod. Fertil. 56:701; Greve and Lehn-Jensen, 1982, Theriogenology 17:91; de Los Santos-Valadez, 1982, Theriogenology 17:85). Previous work has shown that injections of human chorionic gonadotrophin (hCG) following breeding (Sianangama and Rajamahendran, 1992, Theriogenology 38:85) as well as after embryo transfer (Christie et al., 1979, J. Reprod. Fertil. 56:701) enhances pregnancy rates in cattle. Available evidence suggests that the mechanism by which increases in pregnancy rates are achieved is through increases in progesterone (P4) concentration which result from either the stimulation of spontaneous CL (Greve and Lehn-Jensen, 1982, Theriogenology 17:91; de Los Santos-Valadez, 1982, Thefiogenology 17:85), induction of accessory CL (Price and Webb, 1989, J. Reprod. Fertil. 86:303; Rajamabendran and Sianangama, 1992, J. Reprod. Fertil. 95:577) or both. Although the use of hCG has been shown to improve pregnancy rates resulting from both natural and embryo transfer conceptions, little is known about the functional characteristics of the CL induced by hCG. The present experiment was, therefore, designed to examine the development and functional characteristics of CL induced by hCG given on day 7 of the cycle in cattle. Ultrasonography and plasma P4 concentrations were used to characterize the development and function of CL induced by hCG given on day 7 of the bovine estrous cycle (estrus = day 0). Eighteen lactating cycling Holstein cows were randomly assigned to serve as control (CONT, n = 6) or receive hCG on day 7 with (hCGLUT, n = 6) or without (hCGCONT, n = 6) spontaneous CL removal by flank surgery on day 12. Accessory CL were induced in all treated cows except for one in the hCGCONT group. When induced and CONT CL of similar age were compared, mean CL diameter for hCGLUT, hCGCONT and CONT did not differ during days 1 to 4 (p > 0.05). At day 5, CONT CL (29.29 + 1.43 mm) were larger (13 < 0.04) than hCGLUT (24.5 + 1.54 mm) or hCGCONT (24.6 + 1.69 mm). Similarly, CL diameter for hCGLUT and hCGCONT were smaller (13 < 0.0001) than CONT CL between days 10 to 14, inclusive. On day 14 of the cycle, P4 concentration among hCGLUT cows decreased (13 < 0.0001) to 1.10 + 0.94 ng/mL but had increased to 3.06 -t- 0.94 ng/mL by day 18. Corresponding values for hCGCONT and CONT were 5.78 -I- 0.84 and 4.21 -I- 0.77 ng/mL, and 4.51 5:0.84 and 5.53 5:0.77 ng/mL, respectively. Onset of CL regression was similar (p>0.05) between CONT (day 19.71 5: 2.5), hCGLUT (day 17.0 5: 1.5) or hCGCONT (day 17.2 5: 1.3). These results demonstrate that CL induced by hCG given on day 7 of the bovine estrous cycle are functional but appear to be smaller and secrete less P4 than spontaneous CL of similar age. Administration of hCG on day 7 post estrus is a practical tool for improving pregnancy rates in embryo transfer and artificial insemination programs.

Copyright © 1994 Butterworth-Heinemann

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