Modifying current laboratory methods for rapid determination of colostral IgG concentration and colostral IgG absorption in the neonate.

摘要

Neonatal deaths on U.S. dairies represent a great economic loss. Based on the 2007 USDA-NAHMS data is estimated that 22% of calf deaths could be prevented by better maternal colostrum (MC) management. The objectives of the projects in this dissertation were to 1) develop and evaluate rapid and accurate methods to determine MC immunoglobulin (IgG) concentration on-farm, 2) characterize MC composition on U.S. dairy farms and 3) explore methods to determine macromolecule transport in the neonatal calf. The first objective was addressed by utilizing caprylic acid (CA) precipitation to separate IgG from MC, allowing a direct measurement of IgG with a refractometer. Refinement of this test in the laboratory resulted in a strong correlation between refractive index (nD) of the supernatant and the actual IgG concentration, determined by radial immunodiffusion (r = 0.96, P 0.05). The on-farm evaluation of the CA test concluded that breed, lactation, nutrient composition and bacterial contamination did not impact the accuracy of the CA test; however, storage method does impact the accuracy of the test with fresh samples yielding the most accurate results. The nD from the CA test was similar to the nD of whole MC indicating that the precipitation step is not necessary. The second objective was addressed by a nationwide study that evaluated the nutrient, bacterial and IgG content of 827 MC samples. Only 39.41% of samples met the industry recommendations of containing >50 mg IgG/ml and a total plate count 100,000 cfu/ml. This study concluded that while 70.62% of samples contain adequate IgG, bacterial contamination on-farm continues to be a problem and reduces the amount of MC available for feeding calves. The third objective was addressed by two studies; adapting the CA test and refractometry to determine serum IgG concentration and a second study exploring the use of the Ussing chamber as a method to determine macromolecule transport in neonatal tissue. These studies concluded that refractometry of whole serum, without the precipitation step, provides a strong estimate of IgG concentration and that the Ussing chambers are not a valid model to determine macromolecule transport in neonatal intestinal tissue.