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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #133008
Title: EFFECT OF FOLLICLE SIZE AT TIME OF GNRH-INDUCED OVULATION ON LUTEAL FUNCTION AND FERTILITY

Author
item PERRY, GEORGE - U OF MISSOURI
item Geary, Thomas
item LUCY, M - U OF MISSOURI
item SMITH, M - U OF MISSOURI

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2002
Publication Date: 6/1/2002
Citation: PERRY, G.A., GEARY, T.W., LUCY, M.C., SMITH, M.F. EFFECT OF FOLLICLE SIZE AT TIME OF GNRH-INDUCED OVULATION ON LUTEAL FUNCTION AND FERTILITY. JOURNAL OF ANIMAL SCIENCE SUPPLEMENT. 2002. v. 53. p. 45-48.

Interpretive Summary: GnRH in fixed-time AI protocols results in the ovulation of a wide range of follicle sizes. Multiparous beef cows were assigned to one of three treatments: Cyclic or anestrous cows treated with the CO-Synch protocol and anestrous control cows. CO-Synch treated cows received GnRH (100 mcg; im) on d 0 of treatment, and all cows received PG (25 mg; im) on d 7. Forty-eight hours following PG injection, cows received GnRH (100 mcg; im) and were A.I. Blood was collected daily from d 0 to 31 and once weekly from d 34 to 69. Ovarian follicles were measured by ultrasonography on d 7 to 9 to determine growth rate and ovulatory size. Ultrasonography was used to determine pregnancy rates on d 34 and fetal viability on d 41, 48, 55, 62, and 69. Cyclic cows were further postpartum than anestrous cows (P<0.05) on trial start date. Follicular growth rate (d 7 to 9) and size of the ovulatory follicle did not differ among treatments (P>0.05). CO-Synch treated cows had longer luteal lifespan than control cows (19.7 ± 0.9 d and 9.6 ± 1.8 d; P<0.05). Cows that were pregnant on d 41 had higher (P<0.05) concentrations of progesterone than nonpregnant cows from d 19 to d 31. On d 25 post breeding, there was no difference (P>0.05) in pregnancy rates among follicle size groups of CO-Synch cows [4/7(57%), 8/10(80%), 10/13(77%), and 4/6(67%) for 10 to 12, 12.5 to 14, 14.5 to 16, and > 16 mm; respectively]; however, by d 60 post breeding, cows that ovulated 10 to 12 mm follicles maintained fewer pregnancies [2/7(29%); P<0.05] than cows that ovulated 14.5 to 16 [9/12(75%)] mm follicles. In summary, ovulation of smaller follicles does not affect CL formation and progesterone secretion, but may lead to increased embryonic death.

Technical Abstract: GnRH in fixed-time AI protocols results in the ovulation of a wide range of follicle sizes. Multiparous beef cows were assigned to one of three treatments: Cyclic or anestrous cows treated with the CO-Synch protocol and anestrous control cows. CO-Synch treated cows received GnRH (100 mcg; im) on d 0 of treatment, and all cows received PG (25 mg; im) on d 7. Forty-eight hours following PG injection, cows received GnRH (100 mcg; im) and were A.I. Blood was collected daily from d 0 to 31 and once weekly from d 34 to 69. Ovarian follicles were measured by ultrasonography on d 7 to 9 to determine growth rate and ovulatory size. Ultrasonography was used to determine pregnancy rates on d 34 and fetal viability on d 41, 48, 55, 62, and 69. Cyclic cows were further postpartum than anestrous cows (P<0.05) on trial start date. Follicular growth rate (d 7 to 9) and size of the ovulatory follicle did not differ among treatments (P>0.05). CO-Synch treated cows had longer luteal lifespan than control cows (19.7 ± 0.9 d and 9.6 ± 1.8 d; P<0.05). Cows that were pregnant on d 41 had higher (P<0.05) concentrations of progesterone than nonpregnant cows from d 19 to d 31. On d 25 post breeding, there was no difference (P>0.05) in pregnancy rates among follicle size groups of CO-Synch cows [4/7(57%), 8/10(80%), 10/13(77%), and 4/6(67%) for 10 to 12, 12.5 to 14, 14.5 to 16, and > 16 mm; respectively]; however, by d 60 post breeding, cows that ovulated 10 to 12 mm follicles maintained fewer pregnancies [2/7(29%); P<0.05] than cows that ovulated 14.5 to 16 [9/12(75%)] mm follicles. In summary, ovulation of smaller follicles does not affect CL formation and progesterone secretion, but may lead to increased embryonic death.