Antibodies and Inflammation: Fecal Biomarkers of Gut Health in Domestic Ruminants.

Gastrointestinal infections present major challenges to ruminant livestock systems, and gut health is a key constraint on fitness, welfare, and productivity. Fecal biomarkers present opportunities to monitor animal health without using invasive methods, and with greater resolution compared to observational metrics. Here we developed enzyme-linked immunosorbent assays for three potential fecal biomarkers of gut health in domestic ruminants: two immunological (total immunoglobulin [Ig]A and total IgG) and one inflammatory (lactoferrin). We analytically validated the assays, then evaluated whether they could be used as a biomarker of clinically diagnosed gastrointestinal pathologies in cattle (Bos taurus), and finally compared them with helminth fecal egg counts in sheep (Ovis aries). The analytes were detected above the lower limits of detection in cattle, sheep, and goats. Fecal IgA and lactoferrin were higher in cattle with infectious pathologies (strongyles, coccidiosis and symptomatic Johne's disease) compared to healthy controls. Lactoferrin was additionally higher in animals with infectious pathologies compared to noninfectious pathologies, and to asymptomatic Johne's cases. No significant relationships were found with sheep fecal egg counts. These initial findings suggest that fecal IgA and lactoferrin may be useful biomarkers of poor gastrointestinal health in cattle, and that fecal lactoferrin is specific to active inflammation caused by infectious agents. These could be incorporated into the growing suite of noninvasive ecoimmunological tools and used to understand ruminant gut health in a range of species. Applications include improving treatment regimens for gastrointestinal infections, and understanding wildlife physiological responses to infectious challenges.