ARS | Publication request: EVALUATION OF MELENGESTROL ACETATE PROSTAGLANDIN (MGA/PGF), SELECT SYNCH, AND 7 D MGA/SELECT SYNCH ESTROUS SYNCHRONIZATION PROTOCOLS IN BEEF HEIFERS

Submitted to: Montana State University Beef Newsletter
Publication Type: Popular Publication
Publication Acceptance Date: May 1, 2002
Publication Date: June 1, 2002
Citation: FUNSTON, R.N., ANSOTEGUI, R.P., LIPSEY, R.J., GEARY, T.W. EVALUATION OF MELENGESTROL ACETATE PROSTAGLANDIN (MGA/PGF), SELECT SYNCH, AND 7 D MGA/SELECT SYNCH ESTROUS SYNCHRONIZATION PROTOCOLS IN BEEF HEIFERS. MONTANA STATE UNIVERSITY BEEF NEWSLETTER. 2002. v. 7(5). p. 5.

Interpretive Summary: 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=209; 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=211; 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) overall 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.

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=209; 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=211; 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) overall 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.