Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract only
Publication Acceptance Date: 6/1/2000
Publication Date: 6/1/2000
Citation: SASONGKO, B.P., WHITTIER, J.C., GEARY, T.W., SCHUTZ, D.N., DOWNING, E.R., SEIDEL, G.E. REDUCED DOSE GNRH IN SELECT SYNCH AND CO-SYNCH PROTOCOLS TO SYNCHRONIZE ESTRUS OR OVULATION IN BEEF COWS. JOURNAL OF ANIMAL SCIENCE SUPPLEMENT. 2000. v. 78(Suppl. 2). p. 219. Interpretive Summary:
Technical Abstract: Two studies were conducted to using half dose (50%) GnRH injections with Select Synch and CO-Synch synchronization protocols in beef cows. In Trial 1 (Select Synch), primiparous and (P1) multiparous (Pn) crossbred cows at two locations (L1, n=241; L2, n=334) received 50% or 100% GnRH on d 0 of the study. On d 7, all cows received 25 mg of PGF. Estrous detection and am/pm AI took place from d 7 to d 12; clean-up bulls were turned in on d 13. Location had no effect on number of cows observed in estrus, therefore data were pooled across location. There was no difference (P=.96) due to treatment (Trt) in synchronization rate (55% and 55% for 100% and 50% GnRH resp.). AI conception rate (60% and 51%) was not affected (P=.22) by the Trt (for 100% and 50% GnRH resp.). In Trial 2 (CO-Synch), cows received either 50% or 100% GnRH on d 0 and d 9, and 25 mg PGF on d 7. At L3, 204 P1 and Pn cows were assigned to one of four Trt (50:50, 50:100, 100:50, 100:100). At L4, 98 Pn cows received 100% or 50% of GnRH on both d 0 and d 9. Calves were removed from d 7 to d 9, cows were mated by am/pm AI up to 48 h post PGF, then cows not observed in estrus were AI mated. Clean-up bulls went in 14 d after timed AI. Location did not affect synchronization or AI pregnancy rates; therefore data were pooled. There was no difference in synchronization rate between Trt. Dose reductions of GnRH had no effect on AI pregnancy rate (P=.65; 100:100 = 46.2%, 100:50 = 42.3%, 50:100 = 49.0%, 50:50 = 39.2%). We conclude that a half dose of GnRH (50 micrograms) was sufficient to induce fertile estrus and ovulation in beef cows in both synchronization protocols.