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Factors Affecting Retention of Estradiol-17β Silicone Rubber Implants in Ears of Steers

Lilly Research Laboratories, A Division of Eli Lilly and Company, Greenfield, IN 46140

Abstract

A series of trials were conducted to identify the factors causing loss of estradiol-17β (E₂-β) silicone rubber implants from the ears of cattle and to evaluate methods of reducing this loss. Surface application of cattle feces to the ears before implanting resulted in an increase in loss of implants compared with the loss from dry, clean ears (30.6 vs 8.6%; P<.05). Washing ears with a povidone-iodine antiseptic solution before implanting or treating implant sites with an antibiotic after implanting reduced (P<.05) implant loss when ears were coated with the fecal slurry. Coating silicone rubber implants with .5 to 2 mgof oxytetracycline hydrochloride (OTC) reduced (P<.0001) implant loss from 39.8 to 13.8% when ears were coated with fecal slurry. When silicone rubber implants with a 1.5-mg coating of OTC were implanted in cattle before submerging in a dipping vat, implant loss was reduced from 6.2 to 2.7%. In studies designed to evaluate mechanical factors affecting implant loss, implants that were placed in the middle of the ear in tight skin moved .79 cm toward the insertion site during a 14-d period after administration compared with 2.82 cm when placed in the base of the ear. When placed in the middle of the ear in tight skin, only 2 of 399 (.5%) implants were lost from steers submerged in a dipping vat immediately following implantation compared with 42 of 394 (10.7%) when placed in the base of the ear (P<.0001). Implant location and infection at the site of implantation were the primary causes of loss of the silicone rubber implants in these studies. The OTC coating and placement of the implant in tight skin in the middle of the ear both provided significant improvements in implant retention.