Location: Range and Livestock ResearchTitle: The effect of follicle age on pregnancy rate in beef cows) Author
Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2013
Publication Date: 1/31/2014
Publication URL: http://handle.nal.usda.gov/10113/58593
Citation: Abreu, F.M., Geary, T.W., Cruppe, L.H., Madsen, C.A., Jinks, E.M., Pohler, K.G., Vasconcelos, L.M., Day, M.L. 2014. The effect of follicle age on pregnancy rate in beef cows. Journal of Animal Science. 92:1015-1021. Interpretive Summary: During the estrous cycle in beef cattle, cows 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 cow has a “two wave” estrous cycle, then she will ovulate an older follicle than a cow that has a “three wave” estrous cycle. Some scientists suggest that cows 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 301 cows. Cows were programmed to ovulate either a “Young” or “Mature” follicle (5.9 or 9 days old) after estrus. Cows were bred approximately 12 hours after onset of estrus or at a fixed time. Ovaries of cows were examined using an ultrasound to measure growth and size of the ovulatory follicle. Using ultrasound measures, we identified a group of cows (n = 47) that started a new follicular wave later than expected and thus ovulated a follicle that was 2 days younger than the Young follicle group. Pregnancy rate did not differ for cows that ovulated different aged follicles. In summary, age of the ovulatory follicle did not influence pregnancy rate of beef cows.
Technical Abstract: The objective of this study was to determine the effect of age of the ovulatory follicle on fertility in beef cows. Multiparous (n = 171) and primiparous (n = 130) postpartum beef cows in 2 groups (G1 and G2) received estradiol benzoate (EB; 1mg/500kg BW, i.m.) 5.5 d (G1; n = 162) and 6.5 d (G2; n = 139) after ovulation to induce emergence of a new follicular wave, followed by prostaglandin F2a (PGF; 25 mg, i.m.) administration either 5.5 d (Young Follicle; n = 155) or 9.5 d (Mature Follicle; n = 146) after EB. Estrous detection coupled with AI 12 h later (Estrus-AI) was performed for 60 h (Mature Follicle) and 84 h (Young Follicle) after PGF; and cows not detected in estrus within this period received timed-AI, coupled with GnRH, at 72 and 96 h, respectively. Within the first 72 h after PGF, more (P < 0.01) cows in the Mature Follicle treatment (76.6%) than Young Follicle treatment (48.3%) exhibited estrus but through 96 h, proportion detected in estrus (P < 0.05) and interval from PGF to estrus (P < 0.01) were greater in the Young Follicle than Mature Follicle cows (88.6 vs 76.6%, 79.0 ± 0.7 vs 56.7 ± 1.7 h, respectively). Age of the ovulatory follicle at AI was greater (P < 0.01) in the Mature Follicle (9.0 ± 0.06 d) than Young Follicle (5.9 ± 0.03 d) cows, but follicle diameter at AI and pregnancy rates did not differ between Mature Follicle (13.1 ± 0.2 mm; 72.3%) and Young Follicle (13.0 ± 0.1 mm; 67.1%) treatments. Regardless of treatment, diameter of the ovulatory follicle at AI and pregnancy rate were greater (P < 0.01) with estrus-AI (13.3 ± 0.1 mm; 75.1%) than timed-AI (12.6 ± 0.2 mm; 55.4%). Cows in the Mature Follicle treatment that initiated a second follicular wave after EB, but before PGF (Mature Follicle2; n = 47) were induced to ovulate with GnRH and TAI at 72h, when ovulatory follicles were 4 d old and 10.2 ± 0.2 mm in diameter. Pregnancy rate to TAI (51.1%) in Mature Follicle2 did not differ from TAI pregnancy rate (55.4%) across the Mature Follicle and Young Follicle treatments. In summary, age of the ovulatory follicle affected interval to estrus and AI but did not influence pregnancy rate in suckled beef cows. Thus, any differences in fertility that may exist between cows that ovulate a two or three wave dominant follicular are not due to differences in age of the ovulatory follicle.