Production Animal Diseases: The Diagnostic Utility of Colostrum

Abstract

Effective biosecurity at farm, state, national and international levels to prevent and control the spread of important production animal diseases, is essential to minimise the risk of disease outbreaks. Assurance is crucial with regard to the disease status of a population of animals in a growing global livestock market. Assurance is achieved by using testing methods that have a high sensitivity and specificity, i.e. the ability to detect infected and non-infected animals and groups of animals, and ideally are cost effective. The enzyme-linked immunosorbent assay (ELISA) is such a test, being highly versatile, inexpensive and easy to perform. For some production animal diseases, current ELISAs demonstrate poor sensitivity, i.e. detect a lower proportion of infected animals. This poor detection rate may permit the maintenance of infection within livestock populations, posing risks to all levels of biosecurity. Due to the higher concentrations of immunoglobulins (Igs) present in colostrum when compared to serum, colostrum should be able to improve the detection of some important infectious diseases of production animals, improving the assurance of absence of disease. This review presents the underpinning physiological basis of Ig transfer into colostrum, indicates the relative Ig concentrations in serum and colostrum and describes how ELISAs work. Although not the focus of this review, different parameters that can be used for the assessment of diagnostic utility are presented. Targeted production animal diseases investigated in this PhD study are described, and the outcomes of the research into the diagnostic utility of colostrum using vaccinated animals as models of disease, as well as a field study of Johne’s disease are presented. Overall, the premise of this PhD study regarding higher antibody concentrations in colostrum was valid, as the diagnostic sensitivities of the ELISAs were improved when using colostrum compared to serum, while also maintaining diagnostic specificity.