GAPDH and Nematoda infectious disease: The aim of this work was to evaluate the stability of three reference genes – ribosomal protein LO (RPLO), glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and succinate dehydrogenase complex subunit A (SDHA) - in Brazilian Somalis sheep resistant and susceptible to gastrointestinal nematode infections.