The effect of follicle age on conception rate in beef heifers

Authors: ABREU, F - The Ohio State University; CRUPPE, L - The Ohio State University; MAQUIVAR, M - The Ohio State University; UTT, M - The Ohio State University; Madsen, Crystal; VASCONCELOS, JL - Universidade Estadual Paulista (UNESP); MUSSARD, M - The Ohio State University; DAY, M - The Ohio State University; Geary, Thomas

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2013
Publication Date: 2/3/2014
Publication URL: http://handle.nal.usda.gov/10113/58589
Citation: Abreu, F.M., Cruppe, L.H., Maquivar, M., Utt, M.D., Madsen, C.A., Vasconcelos, J.M., Mussard, M.L., Day, M.L., Geary, T.W. 2014. The effect of follicle age on conception rate in beef heifers. Journal of Animal Science. 92:1022-1028.

Interpretive Summary: During the estrous cycle in beef cattle, females generally experience two or three waves of follicular growth on their ovaries. Thus, they ovulate either the second or third wave dominant follicle following estrus. If the female has a “two wave” estrous cycle, then she will ovulate an older follicle than a female that has a “three wave” estrous cycle. Some scientists suggest that cattle with three follicular waves are more fertile than those with two follicular waves. The objective of this study was to determine the effect of age of the ovulatory follicle on fertility. Ovulation was induced in heifers in Montana (n = 162) and Ohio (n = 170). Heifers were programmed to ovulate either a “young” or “mature” follicle after estrus. Heifers were bred approximately 12 hours after onset of estrus. Ovaries of heifers were examined using an ultrasound to measure growth and size of the ovulatory follicle. Estrous response was similar between treatments and locations. Conception rate did not differ for heifers that ovulated a mature or young follicle. In summary, age of the ovulatory follicle did not influence conception rate of beef heifers.

Technical Abstract: The objective of this study was to determine the effect of age of the ovulatory follicle on fertility in beef heifers. Ovulation was synchronized with the 5 d CO-Synch + CIDR program in heifers in Montana (n = 162, Hereford and Angus Crossbred; MT) and Ohio (n = 170, Angus Crossbred; OH). All heifers received estradiol benzoate (EB; 1 mg/500 kg BW, i.m.) 6 d after the final GnRH of the synchronization program to induce follicular atresia and emergence of a new follicular wave (NFW), followed by prostaglandin F2a (PGF; 25 mg, i.m.) administration either 5 d (“young” follicle, YF; n = 158) or 9 d (“mature” follicle, MF; n = 174) after EB. Estrous detection was performed for 5 d after PGF with artificial insemination (AI) approximately 12 h after estrus. Ovarian ultrasonography (MT location only) was performed in YF and MF at EB, PGF, and AI, and 5 d after EB (MF only, which corresponded to the day of PGF for YF heifers). Heifers in MT (n = 20) and OH (n = 18) that were not pre-synchronized or did not initiate a NFW were excluded from further analyses, resulting in 142 and 152 heifers in MT and OH, respectively. Heifers from the MF treatment in MT that initiated a second NFW after EB, but before PGF (n = 14, MF2) were excluded from the primary analysis. In the secondary analysis, the MF2 group was compared to MF and YF treatments in MT. Estrous response was similar (90%; 252/280) between treatments and locations. Proestrus interval (from PGF to estrus) and age of the ovulatory follicle at AI were similar for MF heifers between locations (54.6 ± 1.7 h; 8.3 ± 0.07), but were greater (P < 0.01) for YF heifers in OH (78.5 ± 1.4 h; 5.3 ± 0.06) than MT (67.4 ± 1.6 h; 4.8 ± 0.06; trt x loc, P < 0.01). However, conception rate did not differ for MF (63.8%; 74/116) and YF (67.0%; 91/136) treatments. When the MF2 group was compared to the MF and YF treatments in MT, proestrus interval was longer in the MF2 (92.3 ± 3.7 h; P < 0.01) than in MF and YF treatments. Ovulatory follicle size (10.0 ± 0.3 mm) and follicle age (4.8 ± 0.15 d) at AI in MF2 group was similar to YF (10.4 ± 0.15 mm; 4.8 ± 0.06 d) but smaller and younger (P < 0.01) than in MF treatment (11.0 ± 0.18 mm; 8.3 ± 0.11 d). Conception rate to AI did not differ between MF2, MF and YF (61.5%, 63.3%, and 64.7%, respectively) in MT. In conclusion, manipulation of age of the ovulatory follicle at spontaneous ovulation did not influence conception rate.