Title: Relationship of follicle size and concentrations of estradiol among cows that do and do not exhibit estrus during a fixed-time AI protocol Authors
Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 8, 2013
Publication Date: July 8, 2013
Citation: Swanson, O.L., Larimore, E.L., Perry, B.L., Djira, G.D., Cushman, R.A., Perry, G.A. 2013. Relationship of follicle size and concentrations of estradiol among cows that do and do not exhibit estrus during a fixed-time AI protocol. Journal of Animal Science. 91 (E-Supplement 2):205 (Abstract #223). Technical Abstract: Cows that exhibited estrus around the time of fixed-time AI had greater pregnancy success compared to cows that did not. The objective of this study was to determine the relationship between follicle size and peak estradiol concentration between cows that did or did not exhibit estrus during a fixed-time AI protocol. Beef cows were synchronized with the CO-Synch protocol [GnRH (100 µg) on d -7, PGF2a (25 mg) on d 0, and a second injection of GnRH 48 h after PGF2a (d 2)] in three replicates (n=80, 22 and 24). Follicle size (d 2) and ovulation (d 4) was determined by ultrasonography. Blood samples were collected every 3 (replicates 1 and 2) or 4 (replicate 3) h from PGF2a injection to h 56. Estrus was detected by visual observation with the aid of estrus detection patches, and cows that ovulated were classified as exhibited estrus (n=46) or did not exhibit estrus (n=63). Data were analyzed using the GLM procedure in SAS with replicate as a co-variate. Among all cows (P<0.01) and among cows that exhibited estrus (P<0.01), there was a significant positive relationship between follicle size and peak estradiol concentration, but there was no relationship (P=0.60) between follicle size and peak estradiol concentration among cows that did not exhibit estrus. Cows that exhibited estrus had a larger (P=0.02) follicle (13.4±0.25 mm) and greater (P<0.01) peak estradiol concentration (12.4±0.54 pg/mL) compared to cows that did not exhibit estrus (12.6±0.22 mm and 7.8±0.46 pg/mL). There was no relationship between follicle size and estradiol concentration at the second GnRH injection among all cows (P=0.27), cows that exhibited estrus (P=0.34), and cows that did not exhibit estrus (P=0.34), but cows that exhibited estrus (8.9±0.56 pg/mL) had greater (P<0.01) concentrations of estradiol compared to cows did not exhibit estrus (5.8±0.45 pg/mL). In summary, follicle size had a positive relationship with peak concentrations of estradiol, but only among cows that exhibited standing estrus.