Pathological changes in metabolism of poultry related to increasing production levels.

A continuously increasing production level in poultry breeding has resulted in changes in metabolism. Selection procedures in breeding programmes are focused on an increase in growth rate and on a decrease in feed conversion ratio (less feed intake per unit of deposited tissue). These procedures do not pay attention to the maintenance requirements of birds. Imbalances between production (protein and fat deposition) and supply of energy for maintenance requirements lead to homeostatic dysregulation and to diseases of organs which supply the energy for production and maintenance. The alarming increase in metabolic diseases, such as heart failure syndrome, ascites, and oedema in the lungs and heart, can be directly related to an insufficient oxygen supply. A low oxygen consumption and heat production is one of the mechanisms by which a low feed conversion ratio can be achieved, as is induced hypothyroidism by which physical activity and thus heat production is reduced. Other diseases, such as liver cirrhosis, malabsorption syndrome, sudden death syndrome in broilers, and fatty liver-hemorrhage syndrome, which is nowadays the most important disease in laying hens in the Netherlands, can be related to an imbalance between the production rate and maintenance requirements. A continued selection on the basis of retained energy (in protein and fat) without paying attention to the maintenance requirements of birds will be detrimental for the health and welfare of poultry. These undesirable developments in poultry husbandry should be a challenge for sciences focused on welfare and stress in animals. Such a scientific approach to animals suffering from dysgenic changes in metabolism is needed to solve serious problems in poultry breeding.