Effects of norethisterone acetate on the performance of female racing Greyhounds.

A comparison between the performance of spayed female racing Greyhounds and those suppressed with norethisterone acetate (NTA) was made. Previous work by the author has shown that the racing performance of spayed bitches is the same as that of entire bitches in anoestrus, i.e. spaying is just a permanent anoestrus. The aim was to assess any performance difference between suppression and anoestrus, and thus to determine the effect of norethisterone acetate on race performance. The study was designed as a retrospective case-control. Raceform data was obtained for female racing Greyhounds which had raced, and which were either spayed or suppressed with norethisterone acetate. Analysis showed that suppressed bitches run on average 0.049 to 0.061 s slower over 480 m (centralised models). Since endogenous progesterone (P4) has been linked with reduced race performance, it is logical that progesterone analogues like NTA should have a similar effect. It is likely that the depression in performance is dose-related, but not quantifiable with the current dataset.