|Cushman, Robert - Bob|
Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract only
Publication Acceptance Date: 4/24/2006
Publication Date: 7/1/2006
Citation: Echternkamp, S.E., Cushman, R.A., Allan, M.F. 2006. Relationship of circulating progesterone concentrations to ovulation rate and fertility in cattle selected for twin ovulations [abstract]. Biology of Reproduction. (Supplement):139. (Abstract #301) Interpretive Summary:
Technical Abstract: Lower progesterone concentrations have been associated with decreased embryonic survival and with increased ovulation rate (OR) in dairy cattle. Thus, our objective was to determine whether blood progesterone concentrations during the luteal phase and early embryonic survival were decreased in cattle selected for increased OR for four generations. Blood progesterone concentrations and conception to AI were compared among cows with an OR of one (n = 56), two (n = 174), or three (n = 51). Numbers of preovulatory follicles and corpora lutea (CL) were determined by ultrasonography 12 h after onset of estrus and between 8 and 15 days after AI, respectively; a blood sample for progesterone analysis was collected between d 8 and 15. Pregnancy was diagnosed by ultrasonography at 60.6 +/ 1.1 d after AI. As OR increased, diameter of individual ovulatory follicles (17.1 +/ 0.4, 14.4 +/ 0.2, and 13.1 +/ 0.3 mm, respectively) and of the resultant CL (23.8 +/ 0.6, 20.2 +/ 0.3, and 18.5 +/ 0.4 mm, respectively) decreased (P < 0.01). Conversely, plasma progesterone concentrations increased (P < 0.01) with OR (1 CL = 10.5 +/ 0.6 ng/ml, 2 CL = 14.1 +/ 0.4 ng/ml, and 3 CL = 16.3 +/ 0.6 ng/ml), increased between d 8 (9.3 +/ 1.0 ng/ml) and d 15 (16.9 +/ 1.0 ng/ml), but did not differ overall between pregnant (n = 170) and nonpregnant (n = 111) cows (14.8 +/ 0.4 vs. 12.7 +/ 0.5 ng/ml). Pregnancy rate was lower (P < 0.05) in cows with a single ovulation (46.4%) compared with cows with twin (64.9%) or triplet (64.7%) ovulations. Of 111 pregnant cows with an OR of 2, 64% had two fetuses and 36% had one fetus. Results for 33 pregnant cows with an OR of 3 were 42.4% with three fetuses, 48.5% with two fetuses, and 9.1% with one fetus. In contrast with results for high-producing dairy cows, blood progesterone concentrations increased, but follicle and CL diameter decreased, with OR in cattle selected for twin ovulations. Adjusted for OR, plasma progesterone concentration did not differ between pregnant and nonpregnant cows; therefore, increased pregnancy rates in cows with an OR of 2 or 3 were associated with increased numbers of oocytes released and fertilized.