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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #270089
Title: The effect of Follicle Age on Pregnancy Rate in Beef Cows

Author
item ABREU, F - The Ohio State University
item CRUPPE, L - The Ohio State University
item Madsen, Crystal
item JINKS, E - University Of Missouri
item POHLER, K - University Of Missouri
item DAY, M - The Ohio State University
item Geary, Thomas

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/15/2011
Publication Date: 6/21/2011
Citation: Abreu, F.M., Cruppe, L.H., Roberts, C.A., Jinks, E.M., Pohler, K.G., Day, M.L., Geary, T.W. 2011. The effect of Follicle Age on Pregnancy Rate in Beef Cows. Meeting Proceedings. 62:58-61.

Interpretive Summary: During the estrous cycle in beef cattle, individual females generally experience two or three waves of follicular growth on their ovaries and thus ovulate either the second or third dominant follicle at the subsequent estrus. On approximately d 16 of the estrous cycle, the non-pregnant uterus secretes prostaglandin F'' (PGF), which destroys the corpus luteum on the ovary and allows the dominant follicle present at that time to proceed toward ovulation. If a cow is experiencing a “two wave” estrous cycle, then the follicle that is dominant and would ovulate is older than if a cow were experiencing a “three wave” estrous cycle. The objective of this study was to test the effect of age of the ovulatory follicle on fertility in beef cows. Ovulation was synchronized with the 5 d CO-Synch + CIDR program in multiparous (n = 171) and primiparous (n = 130) postpartum beef cows in two groups (G1 and G2) before application of treatments. Cows in G1 received estradiol benzoate (EB; 1mg/500kg BW, i.m.) 5.5 d (n = 162) and cows in G2 received a similar dose of EB 6.5 d (n = 139) after GnRH-induced ovulation to create follicular turnover and a new wave of follicular growth. Within group, PGF (25 mg, i.m.) was administered either 5.5 d (young follicle, YF; n = 155) or 9.5 d (mature follicle, MF; n = 146) after EB. Preliminary data demonstrated that cows with a young follicle would require 24 h longer after PGF than cows with a mature follicle before they would be in estrus. Thus, estrous detection and AI were performed for 3 d (MF) or 4 d (YF) before cows not yet detected in estrus received timed-AI (TAI) coupled with GnRH administration. Ovarian ultrasonography was performed in YF and MF at EB, PGF and AI, and 5.5 d after EB (MF only). Cows that failed to initiate a new follicular wave after EB (G1, n = 6; G2, n = 5) were excluded from further analyses. Also, cows in the MF treatment that initiated a second follicular wave after EB, but before PGF (G1, n = 25; G2, n = 22) were excluded from further analyses. Within the first 72 h after PGF, more MF cows (76.6%) than YF cows (48.3%; P < 0.01) exhibited estrus. Throughout the estrous detection period, proportion detected in estrus and interval from PGF to estrus were greater (P < 0.01) in the YF than MF treatment (88.6 vs. 76.6%, 79.0 ± 0.7 vs 56.7 ± 1.7 h, respectively). Diameter of the ovulatory follicle was greater (P < 0.01) with estrus-AI (13.3 ± 0.1mm) than TAI (12.6 ± 0.2mm) but did not differ between treatments (MF, 13.1 ± 0.2 mm; YF, 13.0 ± 0.1 mm). Pregnancy rate in the MF (72.3%) and YF (67.1%) treatments did not differ, however, pregnancy rates from estrus-AI (75.1%) was greater (P < 0.01) than from TAI (55.4%). In summary, age of the ovulatory follicle resulted in a longer interval to estrus and to AI in cows with young follicles but did not influence pregnancy rate.

Technical Abstract: The objective of this study was to test the effect of age of the ovulatory follicle on fertility in beef cows. Ovulation was synchronized with the 5 d CO-Synch + CIDR program in multiparous (n = 171) and primiparous (n = 130) postpartum beef cows in two groups (G1 and G2) before application of treatments. Cows in G1 received estradiol benzoate (EB; 1mg/500kg BW, i.m.) 5.5 d (n = 162) and G2 received a similar dose of EB 6.5 d (n = 139) after the final GnRH of the synchronization program to create follicular turnover. Within group, PGF (25 mg, i.m.) was administered either 5.5 d (“young” follicle, YF; n = 155) or 9.5 d (“mature” follicle, MF; n = 146) after EB. In the MF treatment, estrous detection and AI were performed for 3 d after PGF, and timed-AI (TAI), coupled with GnRH administration, was performed at 72 h after PGF for cows not detected in estrus. In the YF treatment, estrous detection was performed for 4 d, with TAI at 96 h after PGF if estrus was not detected. Ovarian ultrasonography was performed in YF and MF at EB, PGF and AI, and 5.5 d after EB (MF only). Cows that failed to initiate a new follicular wave after EB (G1, n = 6; G2, n = 5) were excluded from further analyses. Also, cows in the MF treatment that initiated a second follicular wave after EB, but before PGF (G1, n = 25; G2, n = 22) were excluded from further analyses. Within the first 72 h after PGF, more MF cows (76.6%) than YF cows (48.3%; P < 0.01) exhibited estrus. Throughout the estrous detection period, proportion detected in estrus and interval from PGF to estrus were greater (P < 0.01) in the YF than MF treatment (88.6 vs. 76.6%, 79.0 ± 0.7 vs 56.7 ± 1.7 h, respectively). Diameter of the ovulatory follicle was greater (P < 0.01) with estrus-AI (13.3 ± 0.1mm) than TAI (12.6 ± 0.2mm) but did not differ between treatments (MF, 13.1 ± 0.2 mm; YF, 13.0 ± 0.1 mm). Pregnancy rate in the MF (72.3%) and YF (67.1%) treatments did not differ, however, pregnancy rates in estrus-AI (75.1%) was greater (P < 0.01) than in TAI (55.4%). In summary, age of the ovulatory follicle resulted in a longer interval to estrus and to AI in cows with young follicles but did not influence pregnancy rate.