The rules of greyhound racing prevent a female greyhound racing when in season (pro-oestrus or oestrus), which may occur twice a year in females thus limiting racing opportunities in a comparatively short racing career. Racing performance and behaviour can also fluctuate throughout the reproductive cycle and into dioestrus, therefore trainers and veterinarians may prevent oestrus in racing greyhounds to maintain anoestrus. This paper summarises exempted and prohibited subtances for oestrus regulation.
Anoestrus can be achieved in hard training, through permanent surgical sterilisation, or through pharmaceutical control, which is the most common method used. In Australia, varied anabolic androgenic steroid products were commonly used until 2008 (oral ethyloestrenol has remained exempted), however testosterone administration was commonplace until a threshold for its metabolite 5b-androstane-3a,17b-diol was introduced in 2013. These are now permanently banned prohibited substances.
Our study examined the plasma elimination and urinary excretion of Brevinor-1® (1 mg norethisterone and 35 µg ethinylestradiol) and Levlen® ED (150 µg levonorgestrel and 30 µg ethinylestradiol). Each study involved three greyhounds (one male; two female) following a single oral dose of one of the two oestrous regulating medications. Blood and urine samples were collected at various intervals up to 168 hours post-administration. Results are presented. Ethinylestradiol may be a metabolite of norethisterone in canines, as it is in humans, which was not previously reported.
The Greyhounds Australasia rules now include as exempted substances ethyloestrenol, norethisterone, ethinylestradiol and levonorgestrel when administered orally to a female greyhound and where it has been prescribed by a veterinarian for the sole purpose of regulating or preventing oestrus in a female greyhound.