Plasma concentrations of testosterone and nandrolone in racing and nonracing intact male horses.

This research focuses on the levels of testosterone and nandrolone, two endogenous anabolic steroids, in 2209 blood samples from racing and non-racing intact male horses, collected over two years. It concludes that the current regulatory threshold for testosterone levels in Pennsylvania racing horses should remain at 2000 pg/mL, based on observed population concentrations.

Sample Collection and Analysis

• The researchers analyzed 2209 post-race blood samples from intact male horses collected from March 2008 to November 2010.
• These samples were quantified for testosterone, nandrolone, and other anabolic steroids.
• Out of all the plasma samples collected, 2098 had testosterone levels that could be quantified, these levels being equal to or more than 25 pg/mL.

Testosterone and Nandrolone Concentrations in Racing Intact Male Horses

• The mean concentrations for testosterone and nandrolone in racing intact male horses were 329.2 pg/mL and 96.0 pg/mL respectively.
• However, only 64.6% of such horses had a quantified concentration of nandrolone.
• The study found no relationship between testosterone and nandrolone levels.
• Testosterone concentrations were significantly higher during the months of April through August.
• A statistically significant higher concentration of testosterone was observed in Thoroughbred horses compared to Standardbred horses.

Testosterone Concentrations in Breeding Stallions

• The average testosterone concentrations in breeding stallions were 601.6 pg/mL.
• The study found statistically lower concentrations of both testosterone and nandrolone in racing intact male horses as compared to breeding stallions.

Regulatory Threshold Recommendation

• The study analysed the distribution of testosterone levels amongst racing intact male horses and breeding stallions, finding that 99.5% had levels at or below 1546.1 pg/mL and 1778.0 pg/mL respectively.
• Basing judgement on this observed population distribution, the researchers suggested that the upper threshold plasma concentration of testosterone in horses competing in PA should remain at the current level of 2000 pg/mL.