|Cushman, Robert - Bob|
Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 3/18/2004
Publication Date: 8/1/2004
Citation: Echternkamp, S.E., Cushman, R.A., Christenson, R.K. 2004. Effect of ovulation rate on development of the ovine corpus luteum [abstract]. Journal of Animal Science. 82 (Supplement 1):67. (Abstract #M266) Interpretive Summary:
Technical Abstract: Relationships among ovulation rate (OR), corpus luteum (CL) weight (wt), and numbers of small (< 3mm dia.) and medium (3-6 mm) antral follicles were evaluated for Rambouillet (Ram), 1/2 Romanov x 1/2 Dorset (RxD), Romanov (Rom), and Synthetic III (1/2 Columbia x 1/4 Suffolk x 1/4 Hampshire; SIII) ewes. Ovaries were collected at slaughter on d 14 to 17 of pregnancy, and numbers of CL and of visible follicles were recorded. Ovaries and excised CL were weighed individually. None of the variables differed (P > 0.1; NS) between the left and right ovaries and data were combined. Means (± sem) for OR, ovarian wt (less CL), total CL wt, mean CL wt and number of small and medium follicles are reported in Table 1 for the four genetic groups. Table 1. Genetic effects on OR, ovarian wt, total and individual CL wt, and follicle number Small Medium OR (No. Ovarian Total CL Individual follicles follicles Breed n CL) wt (g) wt (g) CL wt (g) (n) (n) Ram 7 2.3±0.4 4.03±0.33 1.83±0.14 0.80±0.05 42.8±6.0 7.0±1.4 RXD 17 3.2±0.3 3.66±0.22 1.59±0.11 0.53±0.03 43.6±3.8 7.2±0.9 Rom 26 4.8±0.3 3.46±0.17 1.60±0.09 0.35±0.02 39.3±3.1 7.5±0.7 SIII 17 2.4±0.3 4.91±0.22 1.73±0.11 0.71±0.03 37.4±3.8 9.2±0.9 P < 0.01 0.01 NS 0.01 NS NS OR ranged from 2 to 10. Rom ewes had the largest (P < 0.01) OR but the lightest (P < 0.01) individual CL; RxD ewes were intermediate for OR and CL wt relative (P < 0.01) to Rom or to Ram and SIII. Thus, OR and individual CL wt correlated negatively (r = -0.72; P < 0.01). However, total CL wt and number of antral follicles did not differ (P > 0.1) among the genetic groups. SIII ewes had heavier (P < 0.01) ovaries than Rom or RxD. Variables did not differ (P > 0.1) between Ram and SIII. The negative relationship between OR and individual CL weight implies that either 1) the number of follicular cells and(or) their luteinization is compromised in prolific ewes or 2) the progesterone threshold level for negative feedback on LH secretion is similar among individual ewes regardless of prolificacy; thus, development of individual CL is limited by lower LH stimulation in ewes with increased OR.