Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2007
Publication Date: 7/6/2007
Citation: Atkins, J.A., Geary, T.W., Wells, K.J., Lucy, M.C., Smith, M.F. 2007. Factors affecting pre-ovulatory follicle diameter and ovulation rate following GnRH administration in anestrous beef cows. Journal of Animal Science 84(Suppl. 1):158. Interpretive Summary:
Technical Abstract: Induced ovulation of small dominant follicles (< 12 mm) was associated with reduced pregnancy rates and increased late embryonic/fetal loss in beef cows. Factors affecting ovulatory follicle size following follicular wave synchrony remain unclear. The objective of the present study was to determine factors affecting ovulatory follicle size among suckled, postpartum anestrous beef cows. Follicular waves of anestrous beef cows (n = 55) were synchronized with GnRH1 on d -9, and PG on d -2, with (n = 26) or without (n = 29) an exogenous progesterone insert (CIDR) from GnRH1 to PG. Ovulation was induced 48 h after PG with GnRH2 and ovulatory follicle diameter was recorded. Ovulatory response to GnRH1 (Ov1+/Ov1-) and CIDR treatment (CIDR+/CIDR-) resulted in a 2 x 2 factorial design with 9, 17, 11, and 18 cows in the Ov1+/CIDR+, Ov1-/CIDR+, Ov1+/CIDR-, and Ov1-/CIDR- groups, respectively. There was no difference (P > 0.05) in the proportion of Ov1+ (16/20; 80%) and Ov1- (23/35; 66%) cows ovulating at GnRH2, nor was there a difference (P > 0.05) in the proportion of CIDR+ (19/26; 73%) and CIDR- (20/29; 69%) cows that ovulated at GnRH2. There was no interaction (P > 0.05) of ovulation and CIDR treatment on the proportion of cows ovulating to GnRH2 (7/9, 12/17, 9/11, and 11/18 of the Ov1+/CIDR+, Ov1-/CIDR+, Ov1+/CIDR-, and Ov1-/CIDR- treated cows, respectively). Ovulatory follicle diameter at GnRH2 was larger (P < 0.05) in Ov1+ cows (12.3 mm) than Ov1- cows (11.0 mm), but not different (P > 0.05) between CIDR+ (11.8 mm) and CIDR- (11.2 mm) cows. In summary, neither ovulation to GnRH1 nor CIDR administration affected the proportion of cows ovulating to GnRH2. Additionally ovulation to GnRH1, but not CIDR treatment resulted in ovulation of a larger follicle at GnRH2 among suckled, postpartum anestrous beef cows.