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April - June, 2007
Forage Systems Update
Vol 16, No. 2
Comparison of CIDR-based protocols to synchronize estrus prior to
fixed-time AI in beef heifers
D.C. Busch1, D.J. Wilson1, D.J. Schafer2, N.R. Leitman1, J.K Haden2, M.F. Smith1, and D. J. Patterson1
1University of Missouri-Columbia, 2MFA Inc., Columbia, MO
Experimental Procedure
Number of heifers at each location, age, RTS, and weight prior to initiation of synchronization treatments
| Location | No. of heifers | Age (d) | RTS | Weight (lbs) | %Cycling |
| |
| 1 | 78 | 401 | 4.2 | 891 | 77% |
| 2 | 61 | 390 | 3.6 | 764 | 74% |
| | 78 | 405 | 4.1 | 883 | 87% |
| |
| Combined | 217 | 399 | 4.0 | 852 | 80% |
- Animals: Crossbred beef heifers (n=217) at two locations were assigned to treatment within reproductive tract score (RTS) groups by age and weight.
- Estrus detection was performed at location 1 using the HeatWatch® Estrous Detection System (Transmitters were fitted on the day of PG to characterize estrus distribution).
- Two different AI sires were used (Location 1 = 1, and Location 2 = 2). One of the sires used at location 2 was the same sire used at location 1.
- Heifers were maintained on the HeatWatch® system (loc 1) or visually observed (loc 2) for estrus and AI was performed for approximately 24 days following fixed-time AI.
- Pregnancy rate to fixed-time AI was determined with ultrasound 44 days (loc 1) and 58 d (loc 2) after AI.
RESULTS
SUMMARY AND CONCLUSIONS
- Fixed-time AI pregnancy rates were significantly higher (P = 0.02) following the 14d CIDR protocol with TAI at 72 hours (62%) compared to the CO-Synch + CIDR protocol with TAI at 54 hours (47%).
- Fixed-time AI pregnancy rates following the 14d CIDR protocol ranged from 59.0 to 64.1% while pregnancy rates with the CO-Synch+CIDR protocol ranged from 41.0 to 51.3% in this study.
- Over the past 2 years pregnancy rates in field trials resulting from fixed-time AI at 72 hr after administration of the 14-d CIDR protocol were found to be comparable to pregnancy rates after insemination was performed on the basis of observed estrus. The 14-d CIDR protocol offers significant potential to improve results during a synchronized breeding program.
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