Cattlemen's Day, 1986; Kansas Agricultural Experiment Station contribution; no. 86-320-S; Report of progress (Kansas State University. Agricultural Experiment Station and Cooperative Extension Service); 494; Beef; MGA; PGF; Estrus; Synchronization


Three trials were conducted in the spring of 1985 to evaluate the effectiveness of MGA feeding and Prostaglandin (PGF) injection on estrus induction and synchronization. Trials 1 and 2 were both done on a Kansas ranch and involved 70 heifers and 86 cows, respectively. In both trials, all cycling and non-cycling females were fed MGA (7 days in trial 1, 9 days in trial 2) and half of the cows and heifers received a PGF injection. The estrus response was higher (P<.0l) for the cycling heifers with the combination treatment. Both treatments resulted in similar first service conception rates and both were effective in inducing estrus in noncycling heifers. Only a small percentage of the cows in trial 2 were cycling prior to the treatments and only a small percentage of the non-cycling cows responded to the MGA. In trial 3, half of the cycling heifers were fed MGA for 7 days and PGF was injected on day 7. Response to synchronization peaked 96 to 120 hr following MGA withdrawal. Among F1 Angus X Hereford heifers, the MGA-PGF treatment reduced (P<.0l) first service conception rates as compared to controls (55 vs 80%), although a reduction was not seen with F Brahman X Hereford heifers. Conversely, 45-day pregnancy rates tended to be higher among both groups of synchronized heifers (P>.05). The MGA treatment also initiated cyclicity in prepuberal females of both crosses.


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