OBJECTIVE: To compare the analgesic efficacy of administration of butorphanol tartrate,
phenylbutazone, or both drugs in combination in colts undergoing routine castration.
DESIGN: Randomized controlled clinical trial.
ANIMALS: 36 client-owned colts.
PROCEDURES: Horses received treatment with butorphanol alone (0.05 mg/kg [0.023 mg/
lb], IM, prior to surgery and then q 4 h for 24 hours), phenylbutazone alone (4.4 mg/kg
[2.0 mg/lb], IV, prior to surgery and then 2.2 mg/kg [1.0 mg/lb], PO, q 12 h for 3 days), or
butorphanol and phenylbutazone at the aforementioned dosages (12 horses/group). For
single-drug–treated horses, appropriate placebos were administered to balance treatment
protocols among groups. All horses were anesthetized, and lidocaine hydrochloride was
injected into each testis. Physical and physiological variables, plasma cortisol concentration,
body weight, and water consumption were assessed before and at intervals after surgery,
and induction of and recovery from anesthesia were subjectively characterized. Observers
assessed signs of pain by use of a visual analogue scale and a numerical rating scale.
RESULTS: Significant changes in gastrointestinal sounds, fecal output, and plasma cortisol
concentrations were evident in each treatment group over time, compared with preoperative
values. At any time point, assessed variables and signs of pain did not differ significantly
among groups, although the duration of recumbency after surgery was longest for the
CONCLUSIONS AND CLINICAL RELEVANCE: With intratesticular injections of lidocaine, administration
of butorphanol to anesthetized young horses undergoing routine castration had
the same apparent analgesic effect as phenylbutazone treatment. Combined butorphanolphenylbutazone
treatment was not apparently superior to either drug used alone.