Resistance and tolerance to mixed nematode infections in chicken genotypes with extremely different growth rates

•Fast growing genotype is less tolerant to mixed nematode infections.•Resistance to Ascaridia galli is negatively associated with growth rate.•Primary Heterakis gallinarum infection is not associated with growth rate.•Slower growing genotypes are more susceptible to secondary H. gallinarum infection.•Differences amongst genotypes may partly have a nutritional basis.