This sounds promising:

http://www.hkjc.com/english/corporate/racing_news_item.asp?in_file=/english/news/2016-05/news_2016052401539.html

"Identify indirectly, and collectively, the misuse of numerous undetectable or difficult-to-detect substances;

Improve the detection windows for fast-eliminating but long-acting substances;

Perform longitudinal monitoring of biomarkers profiles of racehorses to identify any changes due to the effects of drugs or other forms of doping, the so-called biological passports;

Identify the administration of naturally-occurring (endogenous) prohibited substances;

Differentiate between the surreptitious treatment with a banned substance by a certain route of exposure and the inadvertent exposure to the same substance by another route.”