Effect of exogenous LH pulses on the fate of the first dominant follicle in postpartum beef cows nursing calves

Prolonged postpartum anoestrus in beef cows is due to failure of early dominant follicles to ovulate. It is hypothesized that this failure to ovulate is due to inadequate LH pulse frequency. The objective of this study was to determine whether administration of hourly LH pulses would cause the first dominant follicle to ovulate. In Expt 1, 16 cows received either saline (n = 8) or porcine LH (pLH; 50 micrograms h-1; n = 8) as hourly pulses for 3-5 days from the second day of dominance of the first dominant follicle (day 0). In Expt 2, 21 cows received either saline (n = 7), or 50 micrograms pLH (n = 7) or 100 micrograms pLH (n = 7) as hourly pulses for 3 days. Appropriate ovarian scanning and assays of blood samples were carried out. In Expt 1, the number of dominant follicles that underwent atresia was not affected by increasing the number of LH pulses, but the duration of dominance (days) of the first and second dominant follicles and maximum size (mm) of the second dominant follicle were increased (P < 0.05). Oestradiol concentrations were higher (P < 0.05) in cows given hourly pLH pulses (3.1 +/- 1.2 pg ml-1) compared with controls (1.2 +/- 0.2 pg ml-1). Four of eight treated cows had an anovulatory LH surge. The number of follicle waves to first ovulation was not different (P < 0.05) between control (4.6 +/- 0.9) and pLH treated cows (3.9 +/- 0.5). In Expt 2, four of seven cows given pulses of 100 micrograms pLH h-1 ovulated the first dominant follicle, and the interval from calving to first ovulation was decreased (P < 0.05). In the remaining three cows, the duration of dominance of the first dominant follicle was increased (P < 0.005), the maximum size of the first dominant follicle was greater (P < 0.05), and the interval (days) from the start of infusion to new wave emergence was greater (P < 0.05) compared with cows that failed to ovulate in either the 50 micrograms pLH h-1 or control treatments. In conclusion, hourly pulses of pLH from day 1 after dominance of the first dominant follicle in postpartum beef cows can either prolong dominance or induce it to ovulate. This finding supports the hypothesis that LH pulse frequency is a key determinant of the fate of the dominant follicle in the early postpartum period.

This article has been cited by other articles:

				S. T. Butler, S. H. Pelton, and W. R. Butler Energy balance, metabolic status, and the first postpartum ovarian follicle wave in cows administered propylene glycol. J Dairy Sci, August 1, 2006; 89(8): 2938 - 2951. [Abstract] [Full Text] [PDF]

				J. H. Hampton, B. E. Salfen, J. F. Bader, D. H. Keisler, and H. A. Garverick Ovarian Follicular Responses to High Doses of Pulsatile Luteinizing Hormone in Lactating Dairy Cattle J Dairy Sci, June 1, 2003; 86(6): 1963 - 1969. [Abstract] [Full Text] [PDF]

				R. P. Wettemann, C. A. Lents, N. H. Ciccioli, F. J. White, and I. Rubio Nutritional- and suckling-mediated anovulation in beef cows J Anim Sci, February 1, 2003; 81(14_suppl_2): E48 - 59. [Abstract] [Full Text] [PDF]

				G. A. Perry, F. N. Kojima, B. E. Salfen, J. F. Bader, D. J. Patterson, and M. F. Smith Effect of an orally active progestin on follicular dynamics in cycling and anestrous postpartum beef cows J Anim Sci, July 1, 2002; 80(7): 1932 - 1938. [Abstract] [Full Text] [PDF]

				I. M. Sheldon, D. E. Noakes, and H. Dobson Effect of the Regressing Corpus Luteum of Pregnancy on Ovarian Folliculogenesis after Parturition in Cattle Biol Reprod, February 1, 2002; 66(2): 266 - 271. [Abstract] [Full Text] [PDF]

				M.A. Crowe, P. Kelly, M.A. Driancourt, M.P. Boland, and J.F. Roche Effects of Follicle-Stimulating Hormone With and Without Luteinizing Hormone on Serum Hormone Concentrations, Follicle Growth, and Intrafollicular Estradiol and Aromatase Activity in Gonadotropin-Releasing Hormone-Immunized Heifers Biol Reprod, January 1, 2001; 64(1): 368 - 374. [Abstract] [Full Text]