|Whittier, Jack - COLORADO STATE UNIVERSITY|
|Hallford, Dennis - NEW MEXICO STATE UNIV.|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 11, 2000
Publication Date: November 1, 2000
Citation: GEARY, T.W., WHITTIER, J.C., HALLFORD, D.M., MACNEIL, M.D. CALF REMOVAL IMPROVES CONCEPTION RATES TO THE OVSYNCH AND CO-SYNCH PROTOCOLS. JOURNAL OF ANIMAL SCIENCE. 2000. v. 79. p. 1-4. Interpretive Summary: In choosing the most practical estrous or ovulation synchronization protocol, producers must estimate which females have resumed normal estrous cycles and fertility following calving. This study demonstrates that high pregnancy rates to a timed insemination are possible with both the Ovsynch and CO-Synch protocols. The CO-Synch protocol requires handling cows only three times and thus, would be easier to incorporate into an AI program. Calf removal for 48 h improves pregnancy rates regardless of whether insemination occurs at the time of the second GnRH injection or 24 h later. However, the beneficial effects of calf removal appear to be age related. This information may be valuable for beef producers who have considered using short-term calf removal to improve pregnancy rates.
Technical Abstract: Beef cows (n=473) from two locations were stratified by breed, postpartum interval, age, and AI sire, and randomly allotted to 1 of 4 treatments for synchronization of ovulation. Ovulation synchronization protocols included the Ovsynch protocol with (n=114) or without (n=123) 48-h calf removal from d 7 to 9 (d 0 = 1st GnRH injection) or the CO- Synch protocol with (n=119) or without (n=117) 48-h calf removal (CR) from d 7 to 9. The Ovsynch protocol included administration of GnRH (100 mcg; i.m.) on d 0, PGF2alpha (25 mg; i.m.) on d 7, GnRH (100 mcg; i.m.) on d 9, and timed insemination on d 10. The CO-Synch protocol included the same hormonal injections as the Ovsynch protocol, but with timed insemination on d 9. Blood samples were collected from all cows on d -10 and d 0 for analysis of serum progesterone. Cows with at least one serum progesterone value greater than 1 ng/mL were considered to be cyclic at the time of treatment. Pregnancy rates of cows that received the CO- Synch + CR, Ovsynch + CR, CO-Synch, or Ovsynch protocol (63, 61, 54, and 52% respectively) were not different (P=.50). Pregnancy rates were not different (P=.80) among CO-Synch and Ovsynch treated cows, however, both estrual status and 48-h CR affected pregnancy rates. Pregnancy rates of cyclic and anestrous cows, regardless of synchronization treatment, were 66 and 53%, respectively (P=.01). Pregnancy rates of cows with 48-h CR (62%) were greater (P=.09) than pregnancy rates of cows without CR (53%). The CO-Synch + CR protocol induces a fertile ovulation in cyclic and anestrous cows, requires handling cattle just 3 times, results in high pregnancy rates from timed insemination, and should be a useful program for synchronization of ovulation in beef cows.