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.


METHODS
Randomized complete block study.


METHODS
12 healthy, mature pony stallions.


METHODS
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 forceful expulsion.


CONCLUSIONS
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.
Bedford
S J
SJ
Department of Clinical Studies, School of Veterinary Medicine, New Bolton Center, University of Pennsylvania, Kennett Square 19348, USA.
McDonnell
S M
SM
D000818:Animals; D000981:Antiprotozoal Agents / Q000494:pharmacology*; D006736:Horses / Q000502:physiology*; D008297:Male; D011739:Pyrimethamine / Q000494:pharmacology*; D012098:Reproduction / Q000187:drug effects*; D012661:Semen / Q000187:drug effects; D012726:Sexual Behavior, Animal / Q000187:drug effects; D013091:Spermatogenesis / Q000187:drug effects; D013737:Testis / Q000187:drug effects; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000494:pharmacology*
D000981:Antiprotozoal Agents; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D011739:Pyrimethamine