Synovex® H as a prenatal androgenizing agent in beef cattle: Effects on the implanted pregnant heifer

Abstract

A study was conducted to evaluate the effectiveness of Synovex® H as an agent for prenatal androgenization in beef cattle. Thirty Charolais-cross heifers, exposed to a fertile bull during a 55-d spring breeding season, were randomly assigned to a control group or implanted with three times the normal dose of Synovex® H between days 20 and 75 of gestation. Serum concentrations of testosterone, estradiol, and progesterone, calving rate, and growth performance were determined in the pregnant heifers. Testosterone levels were greater (P < 0.001) in treated heifers than in control heifers. Synovex® H treatment had no affect on estradiol levels. Progesterone levels were lowered (P < 0.05) in treated heifers. Synovex® H treatment decreased (P < 0.05) calving rate and birth weight of calves born to treated heifers. Calving ease scores were not affected by Synovex® H treatment. Weight was not affected; however, average daily gain was improved 7% by Synovex® H treatment (0.88 vs. 0.82 ± 0.04 kg d−1, treated and control heifers, respectively). These results are interpreted to suggest that Synovex® H is not an appropriate androgenizing agent for cattle due to adverse effects on progesterone concentrations during pregnancy and on calving rate. Key words: Cattle, prenatal androgenization, Synovex® H, pregnancy, hormones