SUMMARY
In an effort to characterize the activity of serum γ-glutamyltransferase (ggt) in newborn calves before and after suckling and to explore the usefulness of serum ggt as an indicator of failure of passive transfer in calves, blood samples were collected from the first calves of 48 cows at the time of birth and at 1 day of age. Serum was harvested, and concentrations of IgG and protein and activity of ggt were determined. Morbidity and mortality events were monitored from birth to weaning. Calves suckling colostrum had 10 and 1.3 times greater serum concentrations of IgG and protein, respectively, and a 26 times greater serum activity of ggt, compared with concentrations at birth. Increases in ggt activity and protein concentration were correlated to increases in IgG concentration. Calves classified as having failure of passive transfer (< 800 mg of IgG/dl) had a 9.5 times greater risk of becoming sick prior to weaning, compared with calves determined to have partial failure of passive transfer and clinically normal calves (P= 0.0004). The sensitivity and specificity of a cutoff value of 200 IU of ggt/L of serum for diagnosing failure of passive transfer were 80 and 97%, respectively. The sensitivity and specificity of a cutoff value of 4.2 g of protein/dl of serum for diagnosing failure of passive transfer were 80 and 100%, respectively. The Kappa values for diagnosis of failure of passive transfer, using serum concentrations of IgG vs activity of ggt, IgG vs protein, and ggt vs protein, were 0.72, 0.86, and 0.79, respectively. The value of using ggt activities for diagnosis of hepatic lesions is limited during at least the first week of life in calves that consume adequate amounts of colostrum. The most cost-effective and rapid indicator of passive immune status in this study was determination of serum total protein. Serum activity of ggt also gave reliable indications of passive immune status. Procedures used to determine these values were less expensive and gave results sooner than single radial immunodiffusion for IgG.
