Effects of GnRH treatment on initiation of pulses of LH, LH release, and subsequent concentrations of progesterone

• Published in: Domestic animal endocrinology 2009-11, Vol.37 (4), p.189-195
• Main Authors: Fields, S.D., Perry, B.L., Perry, G.A.
• Format: Article
• Language: English
• Subjects: Analysis of Variance; Animals; application timing; beef cows; Cattle - blood; chemical concentration; CL function; estrus; Estrus - blood; Estrus - drug effects; Female; GnRH; gonadotropin release; gonadotropin-releasing hormone; Gonadotropin-Releasing Hormone - administration & dosage; Gonadotropin-Releasing Hormone - physiology; hormonal regulation; hormone secretion; LH pulses; luteinizing hormone; Luteinizing Hormone - blood; Luteinizing Hormone - drug effects; Luteinizing Hormone - secretion; Models, Statistical; Ovulation - blood; Ovulation - drug effects; Periodicity; Progesterone; Progesterone - blood; temporal variation; Time Factors
• ISSN: 0739-7240; 1879-0054
• DOI: 10.1016/j.domaniend.2009.04.006

Progesterone is essential for establishment and maintenance of pregnancy. One proposed method to increase progesterone is administering GnRH at insemination. However, this method has resulted in conflicting results. Therefore, 2 experiments were conducted to evaluate how administering GnRH at insemination affected pulses of luteinizing hormone (LH) and subsequent progesterone. In Experiment 1, cows were allotted to 2 treatments: (1) GnRH (100 μg) given approximately 12 h after initiation of estrus (n = 5); and (2) Control (n = 5). Blood samples were collected at 15-min intervals for 6 h at 12 (blood sampling period 1), 26 (blood sampling period 2), 40 (blood sampling period 3), 54 (blood sampling period 4), and 68 (blood sampling period 5) h after onset of estrus. Daily blood samples were collected for 17 d. In Experiment 2, cows were allotted into 2 treatments: GnRH administered 10 to 11 h (n = 10) or 14 to 15 h (n = 10) after onset of estrus. Daily blood samples were collected for 17 d. Cows treated with GnRH tended ( P ≤ 0.075) to have greater LH release during blood sampling period 1, tended ( P = 0.095) to have fewer pulses during blood sampling period 2, tended ( P = 0.067) to have greater concentrations of progesterone, and had an earlier ( P = 0.05) increase in progesterone than control cows. Cows treated with GnRH 10 to 11 h after onset of estrus had greater ( P = 0.01) progesterone and an earlier ( P = 0.04) increase in progesterone than cows treated 14 to 15 h. In conclusion, timing of GnRH treatment following onset of estrus influenced pulses of LH and subsequent progesterone.