1 Ghent University, Department of Nutrition, Genetics and Ethology, Merelbeke, Belgium. www.animalnutrition.ugent.be 2 Jimma University, Department of Animal Sciences, Jimma, Ethiopia. www.ju.edu.et/jucavm/node/34 3 Ghent University, Department of Applied Analytical and Physical Chemistry, Ghent, Belgium. http://www.ecochem.ugent.be/nl/ 4 Ghent University, Department of Geology and Soil Science, Ghent, Belgium. www.earthweb.ugent.be 5 Ghent University, Department of Comparative Physiology and Biometrics, Merelbeke, Belgium. www.vetstat.ugent.be * Both authors contributed equally to this work