Salivary IgA: A biomarker for resistance to Teladorsagia circumcincta and a new estimated breeding value.

Abstract

Teladorsagia circumcincta is the dominant nematode of sheep in cool, temperate climates. Faecal nematode egg counts (FEC) are widely used to identify the intensity of infection and as a measure of host resistance to nematodes. However due to density-dependent effects on worm fecundity the relationship between FEC and worm burden is not linear. In addition collecting FEC data is challenging on a practical level and there is a need for more reliable markers of resistance. There are two major known mechanisms of immunity to T. circumcincta: IgE against third stage larvae (L3) and IgA against fourth stage larvae (L4), which inhibits parasite growth. In this study salivary IgA responses were measured in over 5000 animals against L3 antigen by Enzyme Linked Immunosorbent Assay (ELISA). Antigen-specific IgA levels were negatively correlated with FEC (r=-0.26, SE = 0.02) and were heritable (h = 0.16, SE = 0.04) indicating that they can be used to identify resistant animals suitable for inclusion in selective breeding programs. Antigen-specific IgA responses were not negatively correlated with muscle depth. Our analyses indicate that selection for T. circumcincta L3 antigen-specific IgA is possible without impacting on the production traits for the Lleyn breed.