Callaby, R.Hanotte, OlivierConradie van Wyk, IlanaKiara, HenryToye, Philip G.Mbole-Kariuki, Mary NdilaJennings, AmyThumbi, Samuel MwangiCoetzer, Jacobus A.W.Bronsvoort, Barend Mark de ClareKnott, S.A.Woolhouse, Mark E.J.Kruuk, Loeske E.B.2014-11-132014-11-132015-03Callaby, R, Hanotte, O, Conradie Van Wyk, I, Kiara, H, Toye, P, Mbole-Kariuki, MN, Jennings, A, Thumbi, SM, Coetzer, JAW, Bronsvoort, BMDC, Knott, SA, Woolhouse, MEJ & Kruuk, LEB 2015, 'Variation and covariation in strongyle infection in East African shorthorn zebu calves', Parasitology, vol. 142, no. 3, pp. 499-511.0031-1820 (print)1469-8161 (online)10.1017/S0031182014001498http://hdl.handle.net/2263/42569Parasite burden varies widely between individuals within a population, and can covary with multiple aspects of individual phenotype. Here we investigate the sources of variation in faecal strongyle eggs counts, and its association with body weight and a suite of haematological measures, in a cohort of indigenous zebu calves inWestern Kenya, using relatedness matrices reconstructed from single nucleotide polymorphism (SNP) genotypes. Strongyle egg count was heritable (h2 = 23·9%, S.E. = 11·8%) and we also found heritability of white blood cell counts (WBC) (h2 = 27·6%, S.E. = 10·6%). All the traits investigated showed negative phenotypic covariances with strongyle egg count throughout the first year: high worm counts were associated with low values of WBC, red blood cell count, total serum protein and absolute eosinophil count. Furthermore, calf body weight at 1 week old was a significant predictor of strongyle EPG at 16–51 weeks, with smaller calves having a higher strongyle egg count later in life. Our results indicate a genetic basis to strongyle EPG in this population, and also reveal consistently strong negative associations between strongyle infection and other important aspects of the multivariate phenotype.en© Cambridge University Press 2014. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence.Gastrointestinal parasitesStrongyleIndigenous cattleKenyaHeritabilityHaematologyParasite infectionEast African short-horn zebusZebusArticle