Implants in suckling heifer calves intended for cow herd replacements
Dr. Glen Selk, Oklahoma State University
Growth implants have not been widely used in heifer calves because of concern by herd managers about detrimental effects on subsequent reproductive performance of heifers kept as herd replacements. Currently three implants Synovex-C®, Component E-C® (estradiol and progesterone), and Ralgro® (zeranol) have been given FDA approval for use on potential replacement heifer calves. Past reviews of this subject have been quite thorough and generally concluded that one implant given at or after the heifer is 2 months of age has very little impact on future reproductive performance (Hargrove, 1994 and Deutscher, 1994). Also these reviews have both concluded that implanted heifers have significantly greater pelvic area when measured at about one year of age, but these differences are indeed very small at the time the heifer is delivering her first calf at or about two years of age. Consequently, the data on dystocia rate indicates that implanted heifers have no less calving difficulty than do non-implanted counterparts.