|
|
|
Project Number: WVA00321 ASSOCIATION OF FERTILITY WITH TEMPORAL CHANGES IN OVARIAN FUNCTION OF DOMESTIC RUMINANTS Investigators: Inskeep, E.
K., Dailey, R. A., Lewis,
P. E. Termination Date: 09/30/2001 Progress Report: Effects of three short-term treatments with progesterone and estradiol benzoate (EB) on follicular growth, synchrony of estrus, and pregnancy rate after fixed time insemination were compared in lactating, postpartum beef cows on two farms. Cows were bled twice before treatment to determine ovulatory status. In trt. 1, each cow received an intravaginal progesterone insert for 7 d with injection of EB (2mg, i.m.) at the time of device insertion. In trt. 2, the insert was used for 5 d, with injection of EB (2 mg, i.m.) at insertion. Cows in trt. 3 received an insert only for 5 days. All cows received PGF2alpha (25 mg, i.m.) at insert removal, and an injection of EB (1 mg, i.m.) 30 h later. They were inseminated 28 to 30 h after treatment with EB (58 to 60 h after insert removal). Ovarian follicular dynamics were monitored in a random subset of cows in each group. EB terminated growth of the largest ovarian follicle at device insertion in 16/16 and 14/15 cows in trt. 1 and 2, respectively, vs. 11 of 18 in trt. 3. The follicle destined to ovulate was larger in trt. 1 (11.8 +/- 0.7 mm) than in trt. 2 (9.8 +/0 0.3 mm, P<.05). Estrus was detected within an 8-h target period (48 to 56 h after insert removal) in 93, 87 and 81% of cows in trt. 1, 2 and 3 respectively (P>.05); pregnancy rates at 39 d post insemination were 60, 50 and 51% (P>.05). Pregnancy rates (cows pregnant of cows treated) did not differ between cows that were anovulatory or had ovulated at the initiation of treatments (54 vs. 53%), nor among cows that were 28 to 40, 41 to 60, or >60 d postpartum at insemination (43, 59 and 54%, respectively). Injection of PGF2alpha at insert removal and 1 mg EB 30 h later induced the high degree of synchrony of estrus and ovulation necessary for fixed time insemination at 58 to 60 h in lactating beef cows, regardless of ovulatory status. To determine changes in expression of the receptor for PGF2alpha (PGFR), or of enzymes necessary for synthesis of PGF2alpha, CL were collected from cows at 24, 48, or 72 h after initiation of treatment with either saline or PGF2alpha (15 mg in 3 ml, i.m.) every 8 h. Total RNA was harvested and subjected to reverse transcription polymerase chain reaction (RT-PCR) using primers specific for PGFR, prostglandin G/H synthase (PGHS-2), and PGF2alpha synthase (PGFS) to evaluate expression of these genes. Expression increased (P<.01) at 24 and 48 h had declined by 72 h for PGFR, peaked at 48 h (P<.01) for PGHS-2, and increased at 24 and 48 h for PGFS after treatment with PGF2alpha. Treatment with PGF2alpha on d 4 to 7 after estrus induced expression of enzymes necessary for luteal secretion of PGF2alpha and increased expression of the PGFR in bovine CL. These findings indicate that PGF2alpha may be the luteal embryotoxic substance discovered in our previous studies in early postpartum cows. Publications: Ahmad, N., E.C. Townsend, R.A. Dailey, and E.K. Inskeep. 1997. Relationships of hormonal patterns and fertility to occurrence of two or three waves of ovarian follicles, before and after breeding, in beef cows and heifers. Anim. Reprod. Sci. 48:13-28. Lopez-Sebastian, A., A. Gonzalez de Bulnes, J. Santiago, A. Gomez-Brunet, E.C. Townsend, and E.K. Inskeep. 1997. Patterns of follicular development during the oestrous cycle in monovular Merino del Pais ewes. Anim. Reprod. Sci. 48:279-291. Rathbone, M.J., K.L. Macmillan, E.K. Inskeep, S. Burggraaf, and C.R. Bunt. 1998. Fertility regulation in cattle. Journal of Controlled Release 54:117-148. Rathbone, M.J., K.L. Macmillam, W. Jochle, M.P. Boland, and E.K. Inskeep. 1998. Controlled-release products for the control of the estrus cycle in cattle, sheep, goats, deer, pigs and horses. Critical Reviews in Therapeutic Drug Carrier Systems 15:285-380.
|