Growth-promoting implants – the choice for cattle widens

Nutrition with John McKinnon

Relative to first-generation implants, second-generation implants have a greater positive impact on growth and feed efficiency.

This article is destined for press in late September and as such will coincide with the 2020 fall run for both calves and yearlings. For those of you backgrounding or finishing, it is a time where you need to make decisions regarding the health and productivity of incoming cattle. In my last column, I looked at nutritional aspects of starting calves on feed. In this issue, I want to look at a critical aspect of the processing protocol — that being the use of growth-promoting implants.

First, a short review. Growth-promoting implants have been in use for more than 50 years. It can be argued that no other technology has had a greater impact on the efficiency of North American beef production. Physiologically, their use results in increased lean tissue growth (i.e. muscle) at the expense of adipose (i.e. fat) tissue. As a result, the animal grows faster; nutrients are used more efficiently and days to market are reduced. Perhaps most importantly, their use has reduced the industry’s environmental impact (i.e. decreased GHG emissions, reduced water and land use). Further, while challenged by some in society who are interested in a more “natural” lifestyle and by specific companies interested in promoting niche markets, these products have been extensively evaluated by regulatory agencies around the world and found to be safe for both animals and consumers.

When it comes to today’s implant market, it is easy to get confused, as there is a wide array of products available. Differences exist in the type and amount of hormone used, in the timing of release of the hormone package, in the total time the implant is active (i.e. the payout period) and with some products the incorporation of an antibiotic to reduce infection at the implant site (i.e. middle third of the ear). To examine these differences, I will group currently available implants into categories based on the relative timing of commercial release.

First-generation implants have been available since the early 1970s and continue to be used today. These implants are estrogen-based (E) or have estrogen-like activity (i.e. zeranol). Estrogen is a natural hormone found in all mammals, particularly females. Growth promotion is one of its numerous biological functions. Most E-based implants will have either a natural (i.e. estradiol 17ß) or a synthetic (estradiol benzoate with 72 per cent E activity) form of the hormone. In some products, the E is combined with progesterone for use with steers or testosterone for use with heifers.

Based on extensive research, it is widely accepted that this group of implants will improve average daily gain (ADG) by five to 15 per cent and feed efficiency by five to 10 per cent. Their payout period ranges from 60 to 120 days. Relative to newer-generation implants, E-based implants are considered less potent in terms of their growth promoting effect. Depending on hormonal dose, they are used with sucking calves, pasture cattle or as initial feedlot implants.

Second-generation implants came on the market in the 1990s and are combinations of estrogen and trenbolone acetate (TBA). TBA is a synthetic steroid that mimics testosterone activity in terms of growth promotion; however, it is considerably more potent. The concentration of TBA can range from 40 to 200 milligrams (mgs). They can be used as an initial and/or terminal (i.e. the last implant before slaughter) implant.

Relative to first-generation implants, second-generation implants have a greater positive impact on growth and feed efficiency. For example, with their use it is common to see a further five to 10 per cent improvement in ADG and feed efficiency relative to that seen with first-generation implants. The potency of these implants varies directly with TBA concentration. For example, at the lower end, products with 40 mg of TBA are used with grass cattle or as an initial feedlot implant for lighter-weight feeder cattle. Products with 100 to 200 mg of TBA are used in feedlot cattle fed high grain rations in order to promote rapid and efficient weight gains. The most potent in terms of improved growth, feed efficiency and carcass lean content are those implants containing 200 mg of TBA.

The latest group of implants to hit the Canadian market are those that incorporate a form of delayed release technology. This typically involves coating some or all of the pellets during manufacture. Depending on the technology used, the coating will delay or slow the release of the hormone package. As a result, the payout period for these implants is approximately 200 days.

Implants with a combination of coated and uncoated pellets have an initial release of hormone from uncoated pellets and a second release approximately 70 days after implanting. Other implants in this class have all the pellets coated and as a result, the release of the hormonal package is delayed for 70 days. With other products, coating slows the release of the hormone package over the entire payout period. Depending on TBA concentration, these slow release implants can be used in steers and heifers on pasture or in the feedlot. A major benefit of this class of implants is that there is no requirement to re-implant cattle.

Next month, we will look at some of the management decisions involved when implanting cattle, and when choosing the type of implant to use in different feeding scenarios.

About the author


John McKinnon

John McKinnon is a Professor Emeritus at the University of Saskatchewan and a consulting nutritionist who can be reached at [email protected].



Stories from our other publications