Effects of metoclopramide, clenbuterol and butorphanol on ruminoreticular motility of calves.

Rate and amplitude of contractions of the rumen dorsal sac and reticulum of 6 male Holstein calves ages 12 to 20 weeks were monitored with electromyography, strain gauges and an intraruminal pressure catheter. Heart rate and mean arterial pressure were measured with ultrasound. The effects of metoclopramide, a dopamine antagonist, clenbuterol, a beta-2 adrenergic agonist, and butorphanol, a narcotic agonist/antagonist, were observed utilizing dosages bracketing those employed clinically. Metoclopramide significantly decreased the intraruminal pressure peaks associated with cyclical contractions without changing their rate. Clenbuterol had no measurable effect on the ruminoreticulum. Butorphanol totally inhibited ruminoreticular contractions for periods of 6 to greater than 40 min depending on dosage. Only clenbuterol significantly affected cardiovascular function; it increased heart rate and decreased mean arterial pressure. Both metoclopramide and butorphanol produced behavioral changes in the calves.