Measurements of reproductive function in
stallions treated with trimethoprim-sulfamethoxazole and pyrimethamine
Objective-To evaluate the effects of
trimethoprim-sulfamethoxazole and pyrimethamine treatment on various measures of
reproductive function in healthy pony stallions.
Design-Randomized complete block study.
Animals-12 healthy, mature pony stallions.
Procedure-Stallions were assigned to treatment and
control groups balanced for age and various characteristics of reproductive
function. The treated group received trimethoprim-sulfamethoxazole and
pyrimethamine for 90 days during summer and fall; the control group was not
treated. Semen characteristics, sexual behavior, testicular volume, and sperm
production efficiency were evaluated before treatment started and at 30-day
intervals until 60 days after treatment ended.
Results-Effects of treatment were
not detected for semen characteristics, testicular volume, sperm production
efficiency, libido, erection, and quantitative measures of ejaculatory
efficiency. At 30, 60, and 90 days, 4 of 6 treated stallions had unsteadiness
upon mounting, clumsy or weak thrusting, failure to flex the back, and thready
or inapparent ejaculatory pulses that resulted in dribbling of semen rather than
Conclusions and Clinical Relevance-Although
treatment with trimethoprim-sulfamethoxazole and pyrimethamine may not affect
semen quality, testicular volume, sperm production efficiency, erection, or
libido of healthy stallions, treatment may induce changes in copulatory form and
agility and alter the pattern and strength of ejaculation. Stallions that
develop neurologic signs during treatment should be used with caution for
breeding. (J Am Vet Med Assoc 1999;215:1317-1319)