The efficacy of an estradiol-silicone rubber removable implant in suckling, growing and finishing steers.

Abstract

Sixty steer calves, 42 Simmental x Hereford and 18 Hereford, averaging 59 days of age and 78 kg, were assigned to six estradiol-17 beta implant treatments. Implants were cut from cylindrical formed tubes containing a mix of 80% nonpolymerized silicone and 20% microcrystalline estradiol-17 beta by weight and cut into lengths that provided 0, 8.5, 15.6, 30.7, 30.9 and 46.7 micrograms estradiol- 17 beta/day over a 499-day trial period. Two types, a coated and solid implant, were tested at the 31-microgram level; all others were coated with a solid placebo used for the 0-microgram or control treatment. Animal performance was recorded through the suckling, growing and finishing phases of production, and carcass data were collected. Cumulative gains over the 499 days were greater (P less than .05) for the steers given 30.9- and 46.7-micrograms levels than for those given 0-, 8.5- and 15.6-microgram levels, with respective daily gains being .97 and .97 vs .90, .90 and .89 kg; steers given the implant delivering 30.7 micrograms daily tended to gain more (P less than .10) than the controls: .95 vs. 90 kilograms. These values represent a 6% increase in gain over the control with the 30.7-kg coated implant and an 8% increase with the 30.9-microgram solid and 46.7-microgram coated implants. Implants did not improve feed efficiency during a 65-day feedlot period. Neither the amount of estradiol-17 beta nor the type of implant significantly influenced any carcass parameters except maturity. As the dose rate increased, the degree of carcass maturity increased. Type of implant did not affect gain during any period or any of the carcass measures. Results of this study indicate that a single implant of estradiol-17 beta delivering approximately 30.7 micrograms/day will improve weight gains over a long period of time and increase carcass maturity grade of steers.