In last month’s edition of Rural Business, we discussed the value and importance of hormone growth promotant (HGP) implants to the Australian beef industry, Bruce Smith* writes.

Now, we’d like to focus on understanding the differences between various types of implants, so as a reseller you can have confidence in recommending their use in grassfed or grainfed cattle.

There are a number of important differences between implants used in beef cattle, including mode of action, formulation type, payout period, and effect on meat quality.

Most implants contain both oestrogenic and androgenic compounds and are known as combination implants. Some implants (e.g. Compudose) contain oestrogenic compounds only.

Oestrogens (e.g. oestradiol) stimulate the pituitary gland to release more of the body’s own natural growth hormones, increasing satellite cell proliferation, amino acid uptake, and protein deposition.

Androgens (e.g. trenbolone acetate) act directly on muscle tissue, stimulating protein/muscle synthesis and reducing muscle breakdown.

Most implants are presented as compressed powder pellets.

Non-coated compressed powder pellets use a cholesterol carrier and are quickly absorbed into the bloodstream after implantation.

Some newer formulations have a polymer barrier coating that releases the active ingredients at a slower rate than conventional compressed powder pellet formulations.

Compudose implants consist of an inert silicone rubber core covered with a coating of oestradiol-medicated silicone rubber.

The active ingredient is slowly released into the bloodstream to provide a daily dose above the threshold for growth promotion.

The durable core of Compudose reduces crushing or breaking during implantation, ensuring consistent payout and long-term performance.

Implants deliver small increases in the levels of certain hormones above the threshold required for growth.

Once the payout period of the implant ceases, the level of available hormone drops below the threshold, and growth promotion stops.

Different implants have different lengths of payout – bearing in mind that any response in growth rates will vary according to available nutrition.

Compudose 400 is the only product that has a specific payout period of 400 days and a minimum re-implanting interval of 400 days stated on its registered label.

This means producers can be confident that Compudose maximises growth rates year-round, allowing them to implant when it suits them and regardless of pasture conditions at the time.

Certain implants and implant strategies can affect the eating quality of some beef cuts by reducing marbling, increasing ossification (bone growth), and reducing ageing potential. This is noted in the Meat and Livestock Australia Meat Standards Australia (MSA) Beef Information Kit.

In general, cattle treated with implants containing androgenic compounds produce leaner carcasses than cattle treated with oestrogenic compounds. This risk increases with repeat treatment. This has been documented in the MLA report ‘HGP use in the Australian beef industry’ (2009).

The MLA report states that use of combination implants can also reduce marbling score, particularly if implanted during the early stages of growth.

Cattle slaughtered during the payout period of a combination implant may have a higher incidence of dark-cutting meat.

By comparison, the report says oestrogenic compounds have minimal impact on carcass fatness or marbling score, regardless of the length of payout or re-implantation after the payout period has expired.

It is worth noting the potential impact of implants on eating quality can be successfully reduced by careful attention to other management practices as outlined in MSA’s Beef Information Kit.

Implanted cattle are eligible for MSA grading.

In fact, more than a third (35%) of all carcasses achieving MSA grades in 2021 were from implanted cattle and of these, 16% were grassfed. Source: ‘MSA Beef Eating Quality Insights’ (2021). Meat & Livestock Australia.

For these reasons, it is generally accepted that oestrogen-only implants are best used during the growing phases of production.

As long-acting oestrogen implants, Compudose 400 and 200 are ideal for use in ‘whole-of-life’ implant programs or situations where long-term growth promotion is required.

Conversely, combination implants containing trenbolone acetate are best used as a ‘terminal’ implant in finishing situations when adequate nutrition, such as quality pastures, forage crops, supplementary feed, or complete rations, is available.

Always read and follow label directions.

References to reports cited in this article available on request from Elanco.

*Bruce Smith is Elanco account manager for Northern Queensland & Northern Territory.