Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2004
Publication Date: 10/1/2004
Citation: Funston, E.N., Ansotegui, R.P., Lipsey, R.J., Geary, T.W., 2004. Evaluation of three estrous synchronization protocols in beef heifers. Professional Animal Scientist 20:384-387. Interpretive Summary: Estrous synchronization programs need to be inexpensive, effective, and easy to administer. The MGA/PGF protocol provided the highest pregnancy rates and least variability in estrous response; however, the Select Synch protocol provided acceptable pregnancy rates and may be considered for producers who want a shorter synchronization program or when MGA cannot be fed or uniformly consumed. Feeding MGA before the Select Synch program did not provide any benefit in pregnancy rate or decreasing animals in estrus before PGF administration.
Technical Abstract: The objective of this study was to evaluate synchronization, conception, and pregnancy rates of heifers synchronized with MGA/PGF, Select Synch, or MGA/Select Synch. Heifers in the MGA/PGF group (n=208; BW=378 kg) received MGA (0.5 mg/hd/d) for 14 d and an injection of PGF (25 mg) 19 d later. Select Synch heifers (n=213; BW=374 kg) received an injection of GnRH (100 ug) followed by PGF (25 mg) 7 d later. The MGA/Select Synch heifers (n=210; BW=373 kg) were fed MGA (0.5 mg/hd/d) for 7 d, received GnRH (100 ug) the day following the last MGA feeding and PGF (25 mg) 7 d after GnRH. All heifers received PGF on the same day. More (P < 0.01) heifers were observed in estrus before PGF injection in both the Select Synch (20%) and MGA/Select Synch (24%) groups than the MGA/PGF (4%) group. Pregnancy rates for heifers in estrus early were higher (P < 0.05) for both Select Synch (55%) and MGA/Select Synch (63%) compared to MGA/PGF heifers (18%). Synchronization rate (after PGF) was higher (P < 0.01) for MGA/PGF heifers (86%) compared to Select Synch (66%) and MGA/Select Synch (68%); however, conception rate did not differ (P = 0.13), 72, 63, and 62% for MGA/PGF, Select Synch, and MGA/Select Synch, respectively. Overall estrous response was higher (P < 0.05) for MGA/Select Synch (92%) compared to Select Synch (85%) but did not differ (P > 0.05) from the MGA/PGF (89%). The Select Synch (53%) and MGA/Select Synch (57%) protocols provided similar (P = 0.18) AI pregnancy rates compared to the MGA/PGF protocol (62%); however, there were considerably more heifers in estrus before the PGF injection in the protocols using GnRH.