Effect of acepromazine, butorphanol, or N-butylscopolammonium bromide on visceral and somatic nociception and duodenal motility in conscious horses.

The research investigates the effects of the drugs butorphanol, acepromazine, and N-butylscopolammonium bromide (NBB) on pain perception and duodenal motility in horses. It revealed that while these drugs caused predictable changes in sedation and vital signs, they did not consistently exhibit effects on pain relief.

Methodology

• The study involved six adult horses. It was conducted with a randomized order of treatments, and the researchers were blind to the treatment each horse was receiving.
• Vital signs like nose-to-ground height, heart rate, and respiratory rate, as well as pain perception levels, were evaluated. Visceral pain was measured using colorectal and duodenal distention thresholds, while somatic pain was evaluated using thermal threshold.
• Each drug was administered intravenously to the horses. Butorphanol was given as an 18 microg/kg bolus followed by a constant rate infusion at 13 microg/kg/h for two hours. Acepromazine (0.04 mg/kg), NBB (0.3 mg/kg), and a saline solution were administered as a bolus and were followed by a constant rate saline solution infusion for two hours.
• Measurements were taken before treatment and every few minutes for three hours post-treatment. The data collected were analyzed using a three-factor ANOVA and the Bonferroni t test for multiple comparisons.

Results

• The results showed that nose-to-ground height decreased following acepromazine administration. Respiratory rate decreased after acepromazine administration but increased following butorphanol. Heart rate increased briefly after NBB administration.
• Some horses displayed an increase in thermal thresholds following both butorphanol and acepromazine treatment. However, the changes were not significant over time, indicating these drugs did not consistently impact somatic nociception (pain).
• No clear drug effects on duodenal distention or motility were observed. However, an increase in the colorectal distention threshold was significant at various times after acepromazine and NBB administration. This could suggest potential short-term effects on visceral nociception, particularly in the case of acepromazine.

Conclusions

• The study observed that while butorphanol, acepromazine, and NBB caused predictable changes in sedation levels and vital sign readings, their effects on pain relief were not consistent.
• This suggests that while these drugs may have some effects on visceral pain perception, they are not effective anti-nociceptive agents for horses, and their use for this purpose would require further investigation.