1. Department of Equine Science, Hólar University College, 551 Sauðárkrókur, Iceland.
2. Department of Animal Nutrition and Management, Faculty of Veterinary Medicine and Animal Husbandry, Swedish University of Agricultural Sciences, P.O. Box 7024, 750 07 Uppsala, Sweden.
3. Department of Anatomy, Physiology and Biochemistry, Faculty of Veterinary Medicine and Animal Husbandry, Swedish University of Agricultural Sciences, P.O. Box 7011, 750 07 Uppsala, Sweden.