Determination of Passive Immunity in Calves

Calves passively acquire a significant and vital portion of their immune protection from disease through consumption of the first milk (colostrum). The immunoglobulins (antibodies) that are contained in colostrum will help protect the calf from disease for the first several months of life. This process is called passive immunoglobulin transfer. Failure of passive immunoglobulin transfer (FPT) is a serious and ongoing problem in calves. Although many factors that contribute to FPT have been examined, it continues to be an obstacle to profitability. Calves that do not receive adequate colostrum are at increased risk of infection from a variety of disease-causing organisms. Several methods of detecting FPT have been described. Evaluating the status of passive immunity in calves is hindered by deficiencies in the available testing technologies. The most accurate means to assess FPT is determining concentrations of serum immunoglobulin. The predominant type of immunoglobulin transferred from the cow to the calf through colostrum is immunoglobulin G (lgG). Direct measurement of serum concentrations of IgG is usually accomplished using radial immunodiffusion. The value of this test is limited by the high cost involved, the technical expertise required, and the lack of relevance of the test results after the 24 to 48 hr required for the test to run. Several indirect methods of determination are available. These include zinc sulfate turbidity, sodium sulphite precipitation, glutaraldehyde coagulation, and serum refractometry. These are indirect measurements of the immunoglobulin levels of the calf and therefore are subject to artifactual readings due to aberrations in hydration status, total blood protein levels, and other blood attributes. Some of the above tests (zinc sulfate turbidity, sodium sulphite precipitation, and glutaraldehyde coagulation) require the transport of test tubes and reagents to the field. These three tests are semiquantitative and provide estimates of minimal levels or ranges of serum immunoglobulin levels. Refractometry is simple, quick, and inexpensive, but considered the most inaccurate estimator of immunoglobulin status. Gamma-glutamyltransferase (gamma-GT) is a membrane associated enzyme located in multiple sites throughout the body. Gamma-GT is located primarily in cells that have absorptive or secretory functions. Serum level of gamma- GT is recognized as a useful clinical indicator of liver disorders in many species. Activity of gamma-GT in colostrum has been reported to be high in a number of species, including dogs, sheep, cattle, and human beings. In many of these species, serum activity of gamma-GT in neonates that have consumed colostrum is elevated. However, this is not true in all species, with horses being a reported exception. The purposes of this study were to characterize the activity of serum gamma-GT in newborn calves before and after suckling and to explore the usefulnes of serum gamma-GT as an indicator of FPT in calves