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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #223399
Title: Factors associated with ovulatory follicle growth rate and diameter in postpartum beef cows

Author
item ATKINS, JACQUELINE - U OF MISSOURI
item Geary, Thomas
item SMITH, MICHAEL - U OF MISSOURI

Submitted to: American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2007
Publication Date: 7/8/2007
Citation: Atkins, J.A., Geary, T.W., Smith, M.F. 2007. Factors associated with ovulatory follicle growth rate and diameter in postpartum beef cows. Journal of Animal Science 86(E-Suppl. 2/3):250. Abstract #W170.

Interpretive Summary: Beef cows induced to ovulate small (=11mm) follicles had reduced establishment and maintenance of pregnancy compared to cows ovulating large (>11mm) follicles when bred after the CO-Synch protocol (GnRH1 d-9; PGF2a, d-2; and GnRH2 with timed AI on d0). The reason for the presence of small ovulatory follicles is unknown but could be explained by failure to ovulate and synchronize a new follicular wave at GnRH1 or slower growth rate leading to GnRH2. Two experiments were conducted in cycling (n=60) and anestrous (n=55) postpartum, suckling beef cows. Cycling cows were assigned to 1 of 5 treatments based on day of the cycle at GnRH1 of the CO-Synch protocol. The anestrous cow experiment was a 2x2 factorial design based on ovulation or failure to ovulate to GnRH1 and presence or absence of a CIDR from GnRH1 to PGF2a. Only cows ovulating to GnRH2 were used to analyze follicle growth. Factors that affected ovulatory follicle growth rate include day of the estrous cycle at the start of synchronization (among cyclic cows), ovulation and initiation of a new follicular wave (among all cows), and presence of a CIDR from GnRH1 until PGF2a injection (among anestrous cows). It is likely that actively growing follicles will ovulate healthier oocytes that, when fertilized, increase the odds of pregnancy establishment.

Technical Abstract: Beef cows induced to ovulate small (=11mm) follicles had reduced establishment and maintenance of pregnancy compared to cows ovulating large (>11mm) follicles when bred after the CO-Synch protocol (GnRH1 d-9; PGF2a, d-2; and GnRH2 with timed AI on d0). The reason for the presence of small ovulatory follicles is unknown but could be explained by failure to ovulate and synchronize a new follicular wave at GnRH1 or slower growth rate leading to GnRH2. Two experiments were conducted in cycling (n=60) and anestrous (n=55) postpartum, suckling beef cows. Cycling cows were assigned to 1 of 5 treatments (n= 12 per treatment) based on day of the cycle at GnRH1 of the CO-Synch protocol (day 2, 5, 9, 13, and 18 [estrus = d 0]). The anestrous cow experiment was a 2x2 factorial design (n=9 to 18 per treatment) based on ovulation (GnRH1+) or failure to ovulate (GnRH1-) to GnRH1 and presence (CIDR+) or absence (CIDR-) of a CIDR from GnRH1 to PGF2a. Only cows ovulating to GnRH2 were used to analyze follicle growth. Follicle growth from d-5 to 0 was greatest in day 18 cows, followed by day13, 5, 9, and 2 cows (1.1a, 0.72ab, 0.67ab, 0.66b, and 0.47b mm/d, respectively; abP<0.05). The cycling cows that ovulated following GnRH1 had faster follicle growth from d-5 to d0 than did the cows that did not ovulate (0.79 vs. 0.49 mm/d; P<0.05). Follicle growth was slower in day 2 cows than day 9 cows from d-2 to 0 (0.339 vs. 1.29 mm/d, respectively; P<0.05) but was similar among all other treatment groups (1.06, 1.13, and 1.28 mm/d in the day 5, 13, and 18 cows, respectively). In anestrous cows, GnRH1+ cows had greater follicle growth from d-5 to 0 (P<0.01) compared to GnRH1- but similar growth rate from d-2 to 0 (P>0.10), while CIDR+ cows had faster growth rate from d-2 to 0 (P<0.05) compared to CIDR- cows but the growth rate was similar from d -5 to 0. In both experiments, follicle growth was faster (P<0.05) from d-5 to d0 in cows ovulating large (>11mm) compared to small follicles.