The beef cattle industry has once again found itself at the centre of bad news headlines, this time triggered by research that suggests a commonly used cattle growth promotant is increasing the sexual aggression of native male fish.
The story has led to several provocative headlines in mainstream media in the past week, such as “Beef steroid linked to forced fish sex” (ABC) and “Cow steroids leaking into waterways are making fish more randy” (Fairfax).
Both articles highlighted research that has just been published in the scientific journal Hormones and Behaviour by Monash University PHD student Michael Bertram, in conjunction with researchers from Finland.
Their study showed that exposing guppies to “environmentally relevant” levels of trenbolone – in this case 22 nanograms per litre – altered the reproductive behaviour of the fish.
The steroid caused more male guppies to force themselves upon their female mates, rather than allowing the female to choose their mating partner.
By influencing the mating process, exposure to 17β-trenbolone had the potential to profoundly affect individual populations and species, and could have potentially devastating long term evolutionary and ecological impacts, the researchers said.
We highlighted the words “environmentally relevant” above because that is where most uncertainty seems to exist in terms of the relevance of this study is to the Australian beef cattle industry.
It would seem logical to suggest that directly exposing guppies in a laboratory to a hormone used to promote muscle growth in cattle would have a biological effect on the fish.
But the issue that is less clear, and which has not been explored in the media reports to date, is whether implanted Trenbolone can find its way from cattle into surface water in Australia in the volumes required to cause such problems in native fish populations.
Mr Bertram’s report describes to 17β-trenbolone as a “common agricultural pollutant”.
In response to Beef Central’s questions about the basis for that description, Mr Bertram said that approximately 40pc of Australian beef cattle receive growth-promoting implants, based on Meat & Livestock Australia data.
Of those implants, Trenbolone acetate (TBA) is the most commonly used.
Mr Bertram said that after implantation, Trenbolone acetate is broken down to form various metabolites, the most potent of which is 17β-trenbolone—a synthetic steroid with 15–50 times the androgenic and anabolic potency of testosterone.
“This metabolite (as well as others) is then excreted by the cattle and can enter associated water bodies via direct run-off, or often as a result of this excrement being used as fertiliser which can then run off into freshwater systems.”
He said 17β-trenbolone had “repeatedly been detected in freshwater systems associated with cattle operations”. Detected concentrations of 17β-trenbolone ranged from ≤20 ng/L in diffuse run-off, to as high as 162 ng/L in fields directly receiving effluent.
“Our research was intended to inform the use of trenbolone acetate and other hormonal growth promotants, given recent disputes relating to its use (i.e. Russia’s ban on Australian beef imports containing trenbolone residues).
“While this study is the first to show altered male mating behaviour resulting from exposure to environmentally relevant concentrations of 17β-trenbolone, there is a wide range of existing research reporting adverse impacts of exposure to 17β-trenbolone at environmentally relevant concentrations (i.e. developmental and reproductive abnormalities in various species).
“To give one example, recent research conducted at the University of Southern Denmark by Jane Morthorst and colleagues reported that developmental exposure to environmentally relevant concentrations (15.5 and 26.2 ng/L) of 17β-trenbolone caused irreversible masculinisation of zebrafish, whereby exposed populations of fish developed as 100% male (with all fish having been masculinised by 17β-trenbolone).”
When asked if any of the repeated detections of 17β-trenbolone he referred to occurred in Australia, Mr Bertram said the majority of work regarding environmental detections of 17β-trenbolone had been conducted in North America and Europe. He told Beef Central he was not aware of any research having tested for levels of 17β-trenbolone (or other metabolites of trenbolone acetate) in Australian freshwater systems.
Government authorities and industry scientists approached by Beef Central on the question of whether trenbolone contamination of waterways was likely suggested the answer was not as clear cut.
The Australian Pesticides and Veterinary Medicines Authority said only 12 products containing Trenbolone were approved for use in Australia, and all are specifically products which promote the production of muscle mass in cattle.
The APVMA told Beef Central it will now work with the Department of the Environment to review Mr Bertram’s study to identify any new environmental risks for trenbolone and whether any regulatory action may be required.
However, it said that based on current knowledge, there are negligible amounts of ‘broken down’ trenbolone contained in an animal’s waste.
The APVMA spokesperson added that a recent US study was unable to establish a link between hormones found in river water and trenbolone used in upstream feedlots.
“In addition, the current label instructions for use and disposal are designed to minimise the risk of unused trenbolone-containing product entering the environment as a pollutant.”
Animal Medicines Australia, the peak industry body for manufacturers of animal health products, suggested that it was over-reaching to state that 17β-trenbolone had repeatedly been detected in freshwater systems associated with cattle operations.
They explain that the primary metabolite of Trenbolone acetate (TBA) is the 17α-trenbolone, with much lesser amounts of the 17β-trenbolone.
“This is important since the alpha trenbolone (17α-trenbolone) has little biological activity and also has been extensively studied,” AMA chief executive officer Duncan Bremner told Beef Central.
Whether or not surface water around feedlots contained 22ng of 17b trenbolone was also questionable, they said.
A reference to a feedlot cited in a previous US study which generated that figure was not typical, because the manure used had been stored in a pit with no exposure to sunlight and under anaerobic conditions.
Testing for 17β-trenbolone in soil treated with the same manure was non-detectable in many case. Nor were any samples in the water detected.
Cattle Council of Australia chief executive officer Jed Matz said it seemed that the study had been conducted in laboratory conditions, and there was little evidence to suggest trenbolone was entering waterways or affecting fish in Australia.
“Australia has got robust systems in place to manage and track HGP usage, so the risk of HGPs entering the environment or another food source is very low,” Mr Matz said.