Pyruvate Dehydrogenase Deficiency is an inherited metabolic disorder affecting Sussex Spaniels. Affected dogs may present as early as 15 weeks of age with an inability to play as long as littermates. Pyruvate is an important metabolic component needed for energy production in muscle. By 1 year of age affected dogs have clinical signs of exercise intolerance including unwillingness or inability to exercise or play for more than five minutes. Affected dogs may walk slowly, sit to rest often or collapse during exercise or play. After a few minutes of rest dogs may be able to walk and play again but will tire quickly if they continue the activity. Without dietary supplementation affected dogs will die within a few years of age. High numbers of neonatal deaths have been reported in littermates of affected dogs suggesting that many affected dogs die shortly after birth.