Holland adds that it’s also a myth that cattle won’t
perform as well at the feedlot if they were implanted earlier. In addition, use of implants does not result in high
hormone levels in beef. Intact males and females have higher sex hormone levels than do implanted steers. While some international markets, such as the Euro- pean Union, maintain bans on the import of beef from implanted cattle, the World Trade Organization ruled in favor of the U.S. and Canada in fi nding that there was no evidence of a human health risk from beef implants.
Choose the right implant There are more than 25 implant products available (a
comprehensive chart is available at thecattlemanmaga-
zine.com). Some are only suited for feedlot situations, while others are appropriate for calves or for yearlings. The product labels restrict which products should be
used for which sex and phase of production (suckling calves, on pasture, or in the feedlot). The primary difference between products is the hormone contained in them. They are either estrogenic
Use of implants does not result in high hormone levels in
beef. Intact males and
females have higher sex hormone levels than do implanted steers.
(female hormone), androgenic (male hormone), or a combination of the 2. Among the estrogens are estradiol 17-beta, estradiol
benzoate (72 percent as effective as estradiol 17b for growth promotion), and zeranol (33 percent as effective as estradiol 17b). Androgens usually contain testoster- one or trenbolone acetate (an analog of testosterone with a greater anabolic response). The other differ- ence between products is the dose — the greater the concentration, the higher the dose. Holland says replacement heifers can be implanted only once in the suckling or growing phase, but pro-
tscra.org
ducers should consult the label for restrictions on age. Across multiple studies, the effect of implanting on heifer pregnancy rates has ranged from an 11 percent decrease to a 19 percent improvement, but on average, the effects are minimal. If there are any bull calves that may be retained for breeding, those bulls should not be implanted. There are no implants available for use in suckling
calves that combine an androgen and an estrogen. Calves are limited to estrogen products. For stockers, Holland says that in most cases he would recommend use of a combination implant containing both estra- diol and trenbolone acetate. “The 2 hormones work through different pathways to increase animal growth,” he explains. “Estradiol helps increase the frame size of the ani-
mal and ultimately its growth, while trenbolone acetate works directly on muscle cells to ultimately increase muscle mass,” he says. A combination also allows the use of a lower dose
of estrogen. Holland says estrogen increases the main- tenance energy requirement of the animal. “That is important in a stocker situation where we might have low rates of gain or limited forage availability,” he says. “A combination implant is going to give a more con- sistent response at a lower rate of gain (when forage is limited) than an estrogen-only implant.”
Implant technique Implants are applied under the skin, typically un-
der the middle third of the ear. There are 2 ridges of cartilage between the top and bottom of the ear. It’s important to keep that site clean, and to use a disin- fectant in a tray with a roller-type sponge to wipe off the needle between uses. Although only 30 percent of cow-calf operations use
implants, well more than 90 percent of feedlot cattle receive them. Cattle will typically receive implants multiple times in the course of their lives. Most im- plants are expected to be effective for about 100 to 120 days, so it may be advantageous to administer another one after that period of time. When the animals get to the feedlot, the dose typically increases. However, Holland says that studies show implanted cattle out- perform non-implanted animals for as long as 180 days in grazing trials, so it appears the improvement in rate of gain persists beyond what would be expected to be the effective life of the implant. Feed additives, such as ionophores, can also be used. Rather than being an alternative to implants, Holland
May 2015 The Cattleman 47
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