DEVELOPMENT OF A PERSISTENT OVARIAN FOLLICLE AND ASSOCIATED ELEVATED CONCENTRATIONS OF 17-BETA-ESTRADIOL PRECEDING OVULATION DOES NOT ALTERTHE PREGNANCY RATE AFTER EMBRYO-TRANSFER IN CATTLE

It was hypothesized that prolonged elevation in 17 beta-estradiol (E2) preceding ovulation as a result of a persistent ovarian follicle woul d have a detrimental effect on pregnancy rate after Day 7 (behavioral estrus = Day 0) of the estrous cycle. Cows were either treated with ex ogenous progesterone (P4) for 10 d or remained untreated (CON; n = 76) . Cows were treated with 1 of 2 doses of P4 from Day 6 to 16 which was intended to result in either elevated E-2 (EE2; n = 76) or normal E2 (NE2; n = 76) concentration in the circulation. At the initiation of P s treatment, cows received prostaglandin F2 alpha (PGF2 alpha) to elim inate the endogenous source of P4. On Day 16, the exogenous source of P4 was removed from treated cows, while cows in the CON group received PGF2 alpha. A single embryo was transferred into each cow 7 days afte r observation of behavioral estrus. Blood samples were taken on altern ating days during the treatment period to determine concentrations of P4 and E2. The pregnancy rate was determined by ultrasonographic exami nation 25 to 32 d after embryo transfer. There was a treatment-by-day interaction (P < 0.0001) on E2 concentrations in the plasma during the 10-d treatment period. Cows in the EE2 group had a higher concentrati on of E2 by Day 8 (6.1 +/- 0.5 pg/ml) and this concentration remained elevated until PRID removal compared with that of cows in the NE2 (2 /- 0.2 pg/ml) and CON (2.0 +/- 0.3 pg/ml) groups, which had concentrat ions of E2 Similar to those at the initiation of treatment. Pregnancy rates after embryo transfer did not differ (P = 0.56; X-2 = 1.1) among cows in the EE2 (30.7%), NE2 (36.2%) and CON (32.9%) groups. Prolonge d elevation of E2 concentrations associated with the development of a persistent ovarian follicle preceding ovulation did not affect the pre gnancy rate to embryo transfer after Day 7 of the estrous cycle in cow s. (C) 1997 by Elsevier Science Inc.