OBJECTIVE To determine and compare the effects of erythromycin, neostigmine, and metoclopramide on abomasal motility and emptying rate in suckling calves. METHODS 6 male Holstein calves (15 to 40 days of age). METHODS Calves were monitored for 1 hour before being fed milk replacer (60 mL/kg; time, 0 minutes) and then were monitored for another 3 hours. Calves received 6 treatments in randomized order: erythromycin (8.8 mg/kg, IM) at -30 minutes; low-dose erythromycin (0.88 mg/kg, IM) at -30 minutes; erythromycin (8.8 mg/kg, IM) at -30 minutes and neostigmine (0.02 mg/kg, SC) at -30 and 90 minutes; neostigmine (0.02 mg/kg, SC) at -30 and 90 minutes; metoclopramide (0.1 mg/kg, IM) at-30 and 90 minutes; and placebo (2 mL of saline [0.9% NaCl] solution, SC) at -30 minutes. Abomasal volume was calculated from ultrasonographic measurements of abomasal width, length, and height. Abomasal motility and emptying rate were assessed by measuring luminal pressure and change in abomasal volume over time. RESULTS Administration of erythromycin (8.8 mg/kg) increased the frequency of abomasal luminal pressure waves and the mean abomasal luminal pressure and decreased the half-time of abomasal emptying by 37%. Administration of metoclopramide, neostigmine, and low-dose erythromycin (0.88 mg/kg) did not alter abomasal motility, mean luminal pressure, or emptying rate. CONCLUSIONS Results indicated that administration of erythromycin at the labeled antimicrobial dose (8.8 mg/kg, IM) exerted an immediate, marked prokinetic effect in healthy suckling calves, whereas administration of metoclopramide or neostigmine did not alter abomasal motility or emptying rate.