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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #121782
Title: SYNCHRONIZATION OF ESTRUS IN BEEF COWS USING GNRH AND PGF WITH ESTUS AI OR TIMED AI 72 H AFTER PGF WITH OR WITHOUT A SECOND GNRH INJECTION

Author
item Geary, Thomas
item WHITTIER, JACK - COLORADO STATE UNIV
item MORTIMER, R - COLORADO STATE UNIV
item YOUNG, J - REX RANCH WHITMAN NE
item SALVERSON, ROBIN - SELECT SIRES COLUMBUS OH

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 4/3/2001
Publication Date: 6/1/2001
Citation: GEARY, T.W., WHITTIER, J.C., MORTIMER, R.G., YOUNG, J.W., SALVERSON, R.R. SYNCHRONIZATION OF ESTRUS IN BEEF COWS USING GNRH AND PGF WITH ESTUS AI OR TIMED AI 72 H AFTER PGF WITH OR WITHOUT A SECOND GNRH INJECTION. JOURNAL OF ANIMAL SCIENCE SUPPLEMENT. 2001. v. 79(Suppl. 2). p. 131.

Interpretive Summary: This study was designed to evaluate the pregnancy response of cows that were artificially inseminated following synchronization of estrus with the Select Synch protocol and bred following estrus up to 72 h after PGF or time inseminated at 72 h with or without a second GnRH injection. Mature beef cows (n=994) from two herds received GnRH (100 mcg) 1 wk before an injection of PGF (25 mg) to synchronize estrus. Cows (n=257) in herd 1 (mean body condition score, BCS = 5.5, and postpartum interval to AI, PPI = 69 d) were synchronized and bred during the 1997-breeding season, and cows (n=737) in herd 2 (BCS = 4.9, PPI = 77 d) were synchronized and bred during the 1999-breeding season. Cows observed in estrus received AI approximately 12 h later (EAI). Cows not detected in estrus by 72 h after PGF were divided into two groups and time inseminated at 72 h with (TAI+GnRH) or without (TAI) a second injection of GnRH (100 mcg). The 72-h estrous response was 51% and 27% for cows during 1997 and 1999, respectively (P<0.01). Pooled across years, pregnancy rate of EAI cows (60%) was greater (P<0.01) than pregnancy rate of TAI+GnRH (33%) or TAI (27%) cows. During 1997, pregnancy rates were not different (P>0.10) between EAI (61%), TAI+GnRH (54%), and TAI (55%) cows. During 1999, pregnancy rates were higher (P<0.01) for EAI (59%) cows but did not differ (P>0.10) between TAI+GnRH (30%) and TAI (23%) cows. We conclude that incorporating a timed AI at 72 h after PGF for cows synchronized with the Select Synch protocol may be feasible if the 72-h estrous response is high, but caution against timed AI at 72 h in herds when the 72-h estrous response is low. Also, addition of a second injection of GnRH at 72 h may be unnecessary.

Technical Abstract: This study was designed to evaluate the pregnancy response of cows that were artificially inseminated following synchronization of estrus with the Select Synch protocol and bred following estrus up to 72 h after PGF or time inseminated at 72 h with or without a second GnRH injection. Mature beef cows (n=994) from two herds received GnRH (100 mcg) 1 wk before an injection of PGF (25 mg) to synchronize estrus. Cows (n=257) in herd 1 (mean body condition score, BCS = 5.5, and postpartum interval to AI, PPI = 69 d) were synchronized and bred during the 1997-breeding season, and cows (n=737) in herd 2 (BCS = 4.9, PPI = 77 d) were synchronized and bred during the 1999-breeding season. Cows observed in estrus received AI approximately 12 h later (EAI). Cows not detected in estrus by 72 h after PGF were divided into two groups and time inseminated at 72 h with (TAI+GnRH) or without (TAI) a second injection of GnRH (100 mcg). The 72-h estrous response was 51% and 27% for cows during 1997 and 1999, respectively (P<0.01). Pooled across years, pregnancy rate of EAI cows (60%) was greater (P<0.01) than pregnancy rate of TAI+GnRH (33%) or TAI (27%) cows. During 1997, pregnancy rates were not different (P>0.10) between EAI (61%), TAI+GnRH (54%), and TAI (55%) cows. During 1999, pregnancy rates were higher (P<0.01) for EAI (59%) cows but did not differ (P>0.10) between TAI+GnRH (30%) and TAI (23%) cows. We conclude that incorporating a timed AI at 72 h after PGF for cows synchronized with the Select Synch protocol may be feasible if the 72-h estrous response is high, but caution against timed AI at 72 h in herds when the 72-h estrous response is low. Also, addition of a second injection of GnRH at 72 h may be unnecessary.