Influence of exogenous gonadotropin-releasing hormone on ovarian function in beef cows after short- and long-term nutritionally induced anovulation.
The effect of pulsatile infusion of gonadotropin-releasing hormone (GnRH) on follicular function was evaluated in nutritionally induced anovulatory beef cows. After 4 (short; n = 12) or 18 wk (long; n = 12) of anovulation, cows were randomly assigned within anovulatory group to either 2 microg of GnRH treatment or saline (control; i.v.) every hour for 5 d. Ovarian structures were monitored by daily ultrasonography. Growth rate of the largest follicle (P < 0.01) and maximal size of the largest follicle during treatment were greater (P < 0.01) for GnRH vs control cows. At exsanguination after 5 d of GnRH treatment, the size of the second-largest follicle was greater (P < 0.05) in short (i.e., 4 wk) anovulatory cows than in long (i.e., 18 wk) anovulatory cows and the largest follicle tended (P < 0.10) to be larger in long vs short anovulatory cows. Short anovulatory GnRH-treated cows had more small follicles than short anovulatory control cows or long anovulatory GnRH-treated or control cows (anovulation x GnRH; P < 0.10). Follicular fluid (FFL) concentrations of estradiol (P < 0.01) and androstenedione (P < 0.05) were greater in GnRH vs control cows. Concentrations of insulin-like growth factor-I were greater (P < 0.10) in large vs small follicles in cows that were anovulatory for 4 wk, but not in cows that were anovulatory for 18 wk. The amount of insulin-like growth factor-binding protein (IGFBP)-3 in FFL was greater (P < 0.05) in 4- vs 18-wk anovulatory cows. Amounts of IGFBP-2, -4, and -5 were greater (P < 0.001) in FFL of small (< 5 mm) vs large (> or = 5 mm) follicles regardless of treatment. We conclude that pulsatile treatment with GnRH for 5 d stimulates similar growth of the largest follicles in short- and long-term anovulatory beef cows, and that the duration of anovulation is not a major factor that limits follicular growth w hen anovulatory cowsare treated with GnRH. The primary intrafollicular factors associated with increased follicular size were increased concentrations of estradiol, progesterone, and insulin-like growth factor-I,and decreased concentrations of IGFBP-2, -4, and -5. Increased duration of anovulation was associated with decreased concentrations of IGF-I and IGFBP-3 in FFL.
Prado
T M
TM
Department of Animal Science, Oklahoma Agricultural Experiment Station, Oklahoma State University, Stillwater 74078-0425, USA.
Wettemann
R P
RP
Spicer
L J
LJ
Vizcarra
J A
JA
Morgan
G L
GL
D000735:Androstenedione / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D000858:Anovulation / Q000503:physiopathology*; D002417:Cattle / Q000502:physiology*; D004958:Estradiol / Q000032:analysis; D005260:Female; D015571:Follicular Fluid / Q000737:chemistry; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D018969:Insulin-Like Growth Factor Binding Proteins / Q000032:analysis / Q000187:drug effects; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000187:drug effects; D010053:Ovary / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000502:physiology; D011897:Random Allocation; D013217:Starvation; D013997:Time Factors; D014463:Ultrasonography
D018969:Insulin-Like Growth Factor Binding Proteins; D007987:Gonadotropin-Releasing Hormone; D000735:Androstenedione; D004958:Estradiol; D007334:Insulin-Like Growth Factor I