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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #110928
Title: EVALUATION OF THE MELENGESTEROL ACETATE/PROSTAGLANDIN (MGA/PGF) AND MGA/SELECT SYNCH ESTROUS SYNCHRONIZATION PROTOCOLS IN BEEF HEIFERS

Author
item FUNSTON, R - MAES
item ANSOTEGUI, R - MONTANA STATE UNIVERSITY
item THOMPSON, B - MILES CITY VETERINARY CL.
item LIPSEY, J - AMERICAN SIMMENTAL ASSOC.
item ROPP, M - AMERICAN SIMMENTAL ASSOC.
item Geary, Thomas

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2000
Publication Date: 6/1/2000
Citation: FUNSTON, R.N., ANSOTEGUI, R.P., THOMPSON, B.D., LIPSEY, J.J., ROPP, M.D., GEARY, T.W. EVALUATION OF THE MELENGESTEROL ACETATE/PROSTAGLANDIN (MGA/PGF) AND MGA/SELECT SYNCH ESTROUS SYNCHRONIZATION PROTOCOLS IN BEEF HEIFERS. JOURNAL OF ANIMAL SCIENCE SUPPLEMENT. 2000. v. 78(Suppl. 2). p. 118.

Interpretive Summary: Synchronization, conception and pregnancy rates of beef heifers receiving either the Select Synch protocol preceded by 7 d of MGA (MGA/SS) or the traditional MGA/PGF protocol were evaluated. Crossbred beef heifers from one location (n=796) were randomly assigned to treatment and AI sire. Heifers in the MGA/SS group (n=402) were fed MGA (.5 mg/hd/d) for 7 d, received an injection of GnRH (100 mcg) the day following the last MGA feeding and an injection of PGF (25 mg) 7 d after GnRH. Heifers in the MGA/PGF group (n=394) received MGA (.5 mg/hd/d) for 14 d followed 17 d later by an injection of PGF (25 mg). Heifers were observed for estrus continuously during daylight hours beginning 1 d before through 5 d after PGF treatment. Heifers received AI according to the AM/PM rule. Pregnancy status was determined by ultrasound approximately 42 d after AI. Mean body condition scores and weights at time of breeding for the MGA/SS and MGA/PGF heifers were 6.3 and 6.4, and 374 and 380 kg, resp. Synchronization rates were not different (P>.1) between the MGA/SS (85%) and MGA/PGF (83%) treated heifers. Conception and pregnancy rates to AI were 58 and 48% for the MGA/SS heifers and 59 and 49% for the MGA/PGF heifers, resp. (P>.1). Five percent of the MGA/SS and 4% of the MGA/PGF heifers were detected in estrus the day before PGF. By 56 h following PGF, 70% of the MGA/SS and 59% of the MGA/PGF heifers had been observed in estrus. Approximately 90% of synchronized heifers were in estrus by 80 h following PGF in both treatments. In summary, short-term (7 d) MGA feeding preceding the Select Synch protocol produced similar synchronization, conception and pregnancy rates as the traditional MGA/PGF protocol.

Technical Abstract: Synchronization, conception and pregnancy rates of beef heifers receiving either the Select Synch protocol preceded by 7 d of MGA (MGA/SS) or the traditional MGA/PGF protocol were evaluated. Crossbred beef heifers from one location (n=796) were randomly assigned to treatment and AI sire. Heifers in the MGA/SS group (n=402) were fed MGA (.5 mg/hd/d) for 7 d, received an injection of GnRH (100 mcg) the day following the last MGA feeding and an injection of PGF (25 mg) 7 d after GnRH. Heifers in the MGA/PGF group (n=394) received MGA (.5 mg/hd/d) for 14 d followed 17 d later by an injection of PGF (25 mg). Heifers were observed for estrus continuously during daylight hours beginning 1 d before through 5 d after PGF treatment. Heifers received AI according to the AM/PM rule. Pregnancy status was determined by ultrasound approximately 42 d after AI. Mean body condition scores and weights at time of breeding for the MGA/SS and MGA/PGF heifers were 6.3 and 6.4, and 374 and 380 kg, resp. Synchronization rates were not different (P>.1) between the MGA/SS (85%) and MGA/PGF (83%) treated heifers. Conception and pregnancy rates to AI were 58 and 48% for the MGA/SS heifers and 59 and 49% for the MGA/PGF heifers, resp. (P>.1). Five percent of the MGA/SS and 4% of the MGA/PGF heifers were detected in estrus the day before PGF. By 56 h following PGF, 70% of the MGA/SS and 59% of the MGA/PGF heifers had been observed in estrus. Approximately 90% of synchronized heifers were in estrus by 80 h following PGF in both treatments. In summary, short-term (7 d) MGA feeding preceding the Select Synch protocol produced similar synchronization, conception and pregnancy rates as the traditional MGA/PGF protocol.