1. Laboratory of Physiology, Immunology and Genetics of Domestic Animals, Department of Biosystems, Division of Livestock-Nutrition-Quality, Catholic University Leuven, Kasteelpark Arenberg 30, B-3001 Leuven, Belgium
2. Adaptation Physiology Group, Wageningen Institute of Animal Sciences, Wageningen University, P.O. Box 338, 6700 PG, Wageningen, The Netherlands