Abstract: The purpose of this study was to determine the effect of gentamicin sulfate on plasma glucose concentrations after suckling of 2 L of whole cow milk in healthy calves. Five male Holstein-Friesian calves (3 to 7 days of age) were given one of the following treatments in random order: Control, 2 mL of NaCl IM; gentamicin, 6.6 mg kg-1 IM and gentamicin, 4.4 mg kg-1 IM. Serial plasma glucose concentrations were measured at baseline and during 8 h after suckling. During the first 30 min plasma glucose concentrations was lower in gentamicin (p<0.05) group compared to placebo. We proposed that the lower glucose concentrations after gentamicin administration is due to slowing the abomasal emptying rate, post normally consumed milk. Most of diarrheic calves with hypoglycemia have stasis in gastrointestinal motility and gentamicin may be of no benefit as part of treatment and probably exacerbates critical condition in them.