by Cristina Wilkins

A little over a year ago, the Australian racing industry was rocked by news that traces of banned anabolic steroids had been detected in products that are regularly administered to performance mares around the world. Despite being linked to a permitted drug, the finding resulted in two Australian fillies being disqualified from racing for 12 months.

The permitted drug in question is Altrenogest, the active ingredient of oestrus control drugs Regumate® Equine 2.2mg/ml Oral Solution for Horses, Regumate Porcine 0.4% w/v Oral Solution for Pigs and the injectable Readyserve®. And the banned anabolic steroids found were trenbolone and trendione, which are closely related to testosterone.

The news, however, was not entirely unexpected. In 2014, the California Horse Racing Board had warned trainers and veterinarians that these drugs could result in rules violations.

Oestrus control drugs appeared on the equine market around 30 years ago. They are designed to synchronise and accurately control the reproductive cycle of broodmares, and can assist in maintaining pregnancies.

During the time altrenogest is being administered, a mare will not come into season. So today, it is very common for trainers and riders to rely on altrenogest products to surpress the normal reproductive cycle and the changes in behaviour that are associated with it. Altrenogest has become widely used and is permitted under racing and equestrian rules.

The detection of trendione and trenbolone in altrenogest containing drugs, prompted racing and equestrian bodies to remind participants of their zero tolerance stance on anabolic steroids. They now recommend altrenogest is avoided.

But racehorse trainers all over the world have come to rely heavily on these drugs and they are demanding an acceptable trenbolone and trendione threshold is set, so that mares receiving these drugs can be exempt from penalisation should they test positive after a race.

This places the governing bodies in a difficult situation having to balance the aspects of integrity, safety and welfare surrounding these drugs.

Aside from the performance enhancing capabilities, in humans, significant risks have been associated with the long-term use (or abuse) of anabolic steroids, including kidney failure and heart disease.

What is an anabolic androgenic steroid?

Anabolic androgenic steroids (AAS), also simply referred to as ‘anabolic steroids’, are drugs derived from testosterone, a hormone that is produced in the testes of males and, to a much lesser extent, in the ovaries of females.

Testosterone is partially responsible for the developmental changes that occur during puberty and is also involved in controlling the build-up and breakdown of the main biochemical components of all tissues, including muscle.

Testosterone affects muscle growth, so raising its levels in the blood can help athletes increase muscle size and strength, along with some other benefits such as improved endurance.

Because of their performance enhancing capabilities, sports governing bodies have strict rules regarding possession and administration of anabolic steroids to performance horses.

The World Anti-doping Agency is continuously working to improve the testing protocols with the aim of distinguishing between testosterone produced naturally by the body (endogenous) and synthetic compounds (exogenous).

The research?

There seems to be no research on the long-term (off label) use of altrenogest in performance horses. Very little known about how it metabolises into detectable testosterone-related compounds, and whether its administration is giving mares physiological advantages that go beyond a more consistent behaviour.

One man believes that female racehorses have indeed improved their performance since the 1980s, when altrenogest entered the market.

In the following and completely unrelated analysis, Leigh Callinan, a racehorse enthusiast and statistician, presented Horses and People with his own, independent statistical analysis that show that female racehorses have won more big races and awards since 1980.

Are females winning more of the rich horse races than they used to, and are they better than female horses of yesteryear?

by Leigh Callinan

In May 2014, Sports Illustrated published a list1 of what they believed were the 10 all-time best female racehorses in the United States1. Nine of them have raced since 1980, and the other one raced in the 1970’s. This is remarkable; horse racing in the US has been going for hundreds of years, yet the best 10 females have all appeared in recent times. How could that be?

I haven’t found a list of the best ever female racehorses in Australia. So, I’ll offer one (See Table 1 below). I have chosen 1980 as a cut-off point to compare the old and new eras.

Table 1. ‘Best’ Australian female racehorses since 1860

Best Australian female racehorses since 1860

In Table 1, there are nine females in the 120 years 1860 – 1979. If the occurrence of champion female racehorses was a random event, then based on their incidence prior to 1980, we would have expected three (not eight) since 1980.

To even up the years between eras, we can look at the periods (1940 – 1979) and (1980 – 2019). There were six females before 1980 and eight since; not much difference.

I couldn’t find a list of the horses in the American Racing Hall of Fame, which included the sex of the horses. So, I added sex by looking up each entry for 1940 – 2017, in Wikipedia.

The distribution of males and females listed in the American Racing Hall of Fame2, by era, is shown in Table 2 below.

Table 2. The distribution of males and females listed in the American Racing Hall of Fame2, by era.

There is only about a 2% chance that there has not been an increase in the proportion of females racing after 1980 that made it to the American Racing Hall of Fame. The distribution of males and females listed in the Australian Racing Hall of Fame3, by era, is shown in Table 3 below.

Table 3. The distribution of males and females listed in the Australian Racing Hall of Fame3 by era.

Distribution of males and females in the Australian Racing Hall of Fame

There is no significant difference in the proportion of females racing in the two eras that made it to the Australian Hall of Fame.

There is also an award for Australian Horse(s) of the Year4; but it only started in 1968/9. Four females and one male were Horse of the Year more than once.

The distribution of male and female Horses of the Year in Australia, by era, is shown in Table 4 below.

Table 4. The distribution of male and female Horses of the Year in Australia, by era.

There is about a 16% chance that there has not been an increase in the proportion of this award won by females since 1980.

The Cox Plate, Australia’s richest Weight For Age race was also the only wfa race that I could find with a listing of the sex of the winners going back to 1940. The distribution of this race won by male and female horses during 1940 – 2018, by era, is shown in Table 5.

Table 5. Distribution of female and male winners of the Cox Plate since 1940

There is about a 12% chance that there has not been an increase in the proportion of Cox Plates won by females since 1980 .

The results

There is evidence that female racehorses have won more big races and awards since 1980.

Why would that be? It is unlikely to be through genetic selection or management practices; Thoroughbred horses have been around for about 300 years and sudden big improvements have not been noticeable before. After all these years of heavily selecting from a small starting group of horses, you might expect that we would be close to the physiological limit to improvement by selection.

Dr James Rooney, an emeritus professor at the University of Kentucky and an expert on equine biomechanics was quoted in 2001 in The New York Times as saying “the more they learn about horse physiology, the more people begin to realize that this animal has evolved to a certain point and you can’t change it very much [beyond that]”5.

And it seems unlikely that trainers and jockeys now are much better than they used to be in training and preparing female racehorses. And anyway, why would females recently improve more than males?

What has happened since 1980 is the continuing development of medications that can enhance physical development and performance. In a 2009 feature on ‘Drugs in Horse Racing’ in The New York Times, it was concluded that ‘what comes off a veterinarian’s truck and goes into a horse is often perceived to be as important to the performance of a horse as its talent’.

Could it be that these things have improved female horses more than males?


  5. Erica Goode. Thoroughbreds face physical limits to improvement. The New York Times, May 8, 2001.
  6. Drugs in horse Racing. Times Topics. The New York Times. October 5, 2009

In the news

In the United States, the California Horse Racing Board reported in March 2014 that trenbolone had been identified in a specific lot of Regumate® as part of a drug violation enquiry. They warned trainers and veterinarians that the use of Regumate® may result in a trenbolone violation.

In August 2018, Darryl Sherer wrote on that the mare Little Indian trained by Robbie Laing returned a sample positive to Trenbolone (an anabolic androgenic steroid) after racing on September 30, 2017. Another filly, Mrs Hardwick trained by Russell and Scott Camero was tested out of competition on January 22 and returned a blood sample containing levels of Trenbolone and Trendione.

The mares had been treated with Regumate® and/or the similar product Readyserve® both drugs are Altrenogest based.

Read the Racenet story
Read the CHRB report

Is Regumate® worth the risk?

Before last year’s Melbourne Cup, Chris Waller, the trainer of the legendary Winx, told Chris Boots from The Sydney Morning Herald that despite the warning from racing authorities he would continue to race his mares on Regumate®.

“We have done our own testing [for the banned substances trendione and trenbolone] and there has been nothing evident in any of our horses,” he said.

Waller said it was obvious that Regumate® had changed the ability of mares to race consistently. “Just go through a stewards report from 10 years ago – you would see ‘my horse was in season today’. You don’t hear it anymore,” he said.

Read the interview here

This article “Are Female Racehorses Better Than They Used To Be?” was published in Horses and People September-October 2019 magazine.