1. Nutrition Unit, B43, Department of Animal Production, Faculty of Veterinary Medicine, University of Liège, Sart-Tilman, Boulevard de Colonster, 20, B-4000 Liege, Belgium
2. This paper is a part of the thesis submitted by Mehdi Youcef
3. Food Technology Laboratory, B43 bis, Department of Food Science, Faculty of Veterinary Medicine, University of Liège, Sart-Tilman, Boulevard de Colonster, 20, B-4000 Liège, Belgium
4. Veterinary Ecology Unit, Animal Production Department, Veterinary Faculty, University of Liège, Boulevard de Colonster 20, Bât. B43, 4000 Liège, Belgium
5. Dufrasne Isabelle, Faculty of Veterinary Medicine, University of Liège, Station Expérimentale Chemin de la Ferme 6, Bât. B39 4000, Liège, Belgium