15 EFFECT OF DOSE OF ESTRADIOL VALERATE ON OVARIAN FOLLICULAR DYNAMICS IN CIDR-TREATED BEEF COWS
R.J. Mapletoft A , M.G. Colazo A , J.A. Small B , D.R. Ward B and J.P. Kastelic CA WCVM, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. email: reuben.mapletoft@usask.ca
B Agriculture and Agri-Food Canada, Research Centre, Brandon, Manitoba, Canada
C Agriculture and Agri-Food Canada, Research Centre, Lethbridge, Alberta, Canada.
Reproduction, Fertility and Development 16(2) 130-130 https://doi.org/10.1071/RDv16n1Ab15
Submitted: 1 August 2003 Accepted: 1 October 2003 Published: 2 January 2004
Abstract
The objective was to investigate the effect of dose of estradiol valerate (EV) on ovarian follicular growth profiles, intervals to follicular wave emergence and, following CIDR removal, estrus and ovulation in beef cows. On Day 0, 43 non-lactating, crossbred beef cows, 3 to 9 yr of age and at random stages of the estrous cycle, received a CIDR (Bioniche Animal Health; Belleville, Ontario, Canada) and were randomly allocated to one of four groups to receive no further treatment (Control; n = 10), or an injection of 1 mg (n = 11), 2 mg (n = 10), or 5 mg (n = 12) i.m. of EV (Sigma Chemical Co, St. Louis, MO, USA) in 2 mL canola oil. On Day 7, CIDR were removed and cows received 500 μg i.m. of cloprostenol (Estrumate, Schering Plough Animal Health, Pointe-Claire, Quebec, Canada). Ovaries were examined by transrectal ultrasonography once daily until 48 h after CIDR removal to detect ovarian follicle growth profiles, and twice daily thereafter to detect ovulation. Data were analyzed by ANOVA (LSD and Bartlett’s tests) and chi-square procedures. One cow (5 mg EV group) lost the CIDR and was removed from all analyses. There was an effect of day (P < 0.0001) on CL diameter, but the effects of treatment (P = 0.3), and the treatment-by-day interaction (P = 0.1), were not significant. Follicular wave emergence occurred within 7 d in 7/10 (70%) Control cows and 31/32 (97%; P < 0.04) EV-treated cows (one cow in late diestrus at the time of treatment did not respond to 1 mg EV). Mean (±SD) interval from treatment to wave emergence was longer (P < 0.03) in cows treated with 5 mg EV (4.8 ± 1.2 d) than in those treated with 1 mg (3.2 ± 0.9 days) or 2 mg EV (3.4 ± 0.8 days), while Control cows were intermediate (3.8 ± 2.0 days). Although follicular wave emergence tended (P < 0.09) to be more synchronous in cows receiving EV, intervals from CIDR removal to estrus (P = 0.7) and ovulation (P = 0.8) did not differ among groups. Diameter of the dominant follicle was smaller (P < 0.04) at CIDR removal and tended to be smaller (P < 0.08) just prior to ovulation in the 5 mg EV group (8.5 ± 2.2 and 13.2 ± 0.6 mm, respectively) than in the Control (11.8 ± 4.6 and 15.5 ± 2.9 mm, respectively) or 1 mg EV (11.7 ± 2.5 and 15.1 ± 2.2 mm, respectively) groups, with the 2 mg EV group (10.7 ± 1.5 and 14.3 ± 1.7 mm, respectively) intermediate. Diameter of the dominant follicle at CIDR removal was less variable (P < 0.01) in the 2 and 5 mg EV groups than in the Control group and intermediate in the 1 mg EV group. In summary, dose of EV affected follicular dynamics, interval to and synchrony of follicular wave emergence, and dominant follicle diameter at CIDR removal and just prior to ovulation in CIDR-treated cows. However, interval from CIDR removal to estrus and ovulation was not affected by treatment. Results suggest that a dose of 2 mg EV may be most efficacious in synchronizing follicular wave emergence in CIDR-treated cows.
