Effect of abomasal emptying rate on the apparent efficiency of colostral immunoglobulin G absorption in neonatal Holstein-Friesian calves

Inadequate absorption of colostral IgG in calves increases the risk of morbidity and death and is an important source of economic loss to the dairy industry. We hypothesized that an increased rate of abomasal emptying in colostrum-fed calves would be associated with an increased apparent efficiency of absorption (AEA) of colostral IgG. This is because an increase in abomasal emptying rate causes IgG to reach the site of absorption in the small intestine earlier and at a higher luminal concentration. The main objective was, therefore, to determine the association between the AEA of colostral IgG and abomasal emptying rate in neonatal calves. Twenty-four neonatal Holstein-Friesian calves were randomly assigned to one of the following treatments: control, 2mL of 0.9% NaCl intramuscularly; erythromycin, 8.8mg/kg of body weight intramuscularly; ivermectin, 200μg/kg intravenously; and gentamicin, 6.6mg/kg intramuscularly. These treatments were selected because we have previously demonstrated that erythromycin and ivermectin increase, and gentamicin decreases, the rate of abomasal emptying in milk-fed calves. Calves were fed 3L of pooled cow colostrum containing acetaminophen (50mg/kg of body weight) by oroesophageal intubation at 1h of age and 30min after each treatment was administered. Jugular venous blood samples were obtained periodically after the start of feeding. Abomasal emptying rate was assessed by the time to maximal plasma acetaminophen concentration. Erythromycin increased and gentamicin decreased the abomasal emptying rate and AEA of colostral IgG compared with control, respectively, whereas ivermectin had no effect. Using data from all 24 calves, the AEA of colostral IgG was linearly and negatively associated with abomasal emptying rate (R²=0.22). We conclude that the abomasal emptying rate is an important determinant of the AEA of colostral IgG. Identifying a non-antimicrobial method for increasing abomasal emptying rate will provide a practical and effective method for facilitating transfer of passive immunity in colostrum-fed dairy calves.