Synchronization of Bos indicus × Bos taurus cows for timed artificial insemination using gonadotropin-releasing hormone plus prostaglandin F2α in combination with melengestrol acetate
2003
Hiers, E.A. | Barthle, C.R. | Dahms, MK.V. | Portillo, G.E. | Bridges, G.A. | Rae, D.O. | Thatcher, W.W. | Yelich, J.V.
Nonlactating Bos indicus × Bos taurus cows were used in three herds to determine the efficacy of different PGF2α treatments in combination with GnRH and melengestrol acetate (MGA) for a timed artificial insemination protocol. The start of the experiment was designated as d 0, at which time cows were assigned a body condition score and received 100 μg of GnRH. Cows were fed MGA (0.5•mg•cow−1•d−1) on d 1 to 7. On d 7, cows received either a single injection of PGF2α (Lutalyse sterile solution; 25 mg; n = 297), a single injection of cloprostenol sodium (Estrumate; 500 μg; n = 297), or half the recommended dose of PGF2α (12.5 mg; n = 275) on d 7 and 8. On d 10, all cows were artificially inseminated and received 100 μg of GnRH. Pregnancy rates to the timed artificial insemination (39%) were not affected by treatment, herd, or treatment × herd. There was an effect (P < 0.01) of artificial insemination sire on timed artificial insemination pregnancy rate for one herd, but not the other two herds. Herd influenced (P < 0.05) 30-d pregnancy rates, but there were no treatment or treatment × herd effects as 72.3% of the cows became pregnant during the first 30 d of the breeding season. Results indicate that the type of PGF2α treatment administered 7 d after GnRH did not influence timed artificial insemination pregnancy rates in nonlactating Bos indicus × Bos taurus cows.
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