Abstract
The use of a rapid plasma progesterone enzymeimmunoassay (EIA) to select nonlactating beef cows for prostaglandin treatment in an estrus synchronization program was evaluated. Plasma from 73 Angus X Hereford cows was evaluated for progesterone (P4) weekly. Cows with P4 > 5 ng/ml were injected either intramuscularly (I.M.) with 25 mg dinoprost tromethamine or subcutaneously with 1 mg of fenprostalene and then bred by artificial insemination (AI) by appointment at 72 and 96 h. Cows with plasma P4 < 5 ng/ml were reevaluated at weekly intervals. All 73 cows were injected within three sampling periods. Cows not conceiving during the initial trials were reprocessed. Plasma P4 was evaluated at first AI and at Day 21 following AI. All cows were palpated per rectum for pregnancy at approximately 42 d following AI. Following two breeding cycles, 56 of 73 cows (77%) were pregnant. A total of 44 of 73 cows (60%) and 12 of 24 cows (50%) were pregnant following the first and second breeding cycles, respectively. The pregnancy rates between cows injected with dinoprost tromethamine and those injected with fenprostalene were not different (P > 0.05).
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