Feedlot medicine and management. Implants.

Growth-promoting implants have been used extensively in beef production for over 30 years. Significant changes in implants and implanting strategies have occurred. Prior to 1987, available implants were estrogenic agents that metabolically enhanced nutrient use to enhance growth. These products tend to increase intake but significantly improved feed efficiency and daily gains. In 1987, an androgenic (tissue-building) agent, TBA, was approved for use in growth-promoting implants. The androgenic implant enhanced muscle growth without increasing intake, thereby adding an additional 3% to feed efficiency and 3% to 5% to daily gains. Today, implants have become almost "designer" products with varied doses and combinations of estrogenic and androgenic agents. Although implants tend to be most widely used in feedyards, numerous implant strategies are available for use in cattle from the suckling through finishing phases of production. Consistent responses to lifetime programs depend not only on product use but on timing and sequence as well. Lifetime implant programs should be designed to obtain an optimum growth and efficiency response while minimizing expression of live animal side effects and adverse effects on carcass traits. Recent studies suggest that using implants with increasing potency in succession allows for the greatest animal lifetime gain (up to 150 lb) while maintaining or slightly improving postweaning feed conversion when compared with that of nonimplanted cattle. Implant strategies that match implant dose or potency to animal age, weight, and production desired are recommended. Beginning in the preweaning period with low-potency products and ending in the postweaning period with high-potency androgenic-containing implant products which complement the estrogenic response, maintain the positive carry-over effects of previous implants. Implant programs should be designed to maintain hormone blood levels within an optimum response range. Hormone levels below or above this range should be avoided once implant programs are initiated.