Complex dietary factors as causes of bone and articular leg diseases in poultry. A review

Abstract

The most frequent syndromes involved in leg weakness problems of poultry are chondrodystrophy, twisted legs problems, rickets, tibial dyschondroplasia (T.D.) and femoral head necrosis (osteoporosis). T.D. can result from several imbalances between nutrients. When calcium and available phosphorus (aP) dietary levels are high enough to avoid rickets, a phosphorus excess relatively to calcium (Ca : aP ratio < 2) clearly increases T.D. incidence. Such a problem can appear when wheat is used instead of corn, due to the high availability of wheat phosphorus for poultry. T.D. incidence is also very sensitive to chloride excess (and more generally to anion excess) relatively to sodium and potassium. The severity of chondrodystrophy resulting from zinc deficiency is aggravated by polyinsaturated fatty acids and reduced by supplementations of saturated fatty acids, pyridoxine, histidine, vitamin E or inhibitors of prostaglandin synthesis. Fatty acids act in a similar way towards biotin deficiencies. Twisted legs can be induced by high tannin sorghum while rye contains a rachitogenic factor. High levels of rapeseed meal, lupin and field beans in starter diets can also induce leg deformities. Sojabean can increase T.D. incidence in some particular cases. Runting syndrome is a new syndrome often including the appareance of brittle bones at two weeks and of femoral head necrosis at six weeks of age. This syndrome seems to be related to a malabsorption problem due to an infections agent (reovirus ?) and mainly affecting liposoluble vitamins and minerals. Several aflatoxicosis induce some similar clinical signes, particulary bone fragilisation. Leg problems are increased by high dietary energy or protein levels. A slight feed restriction, especially around three weeks of age, reduces T.D. incidence and deserves further investigation. To use daily fasting periods or fractionnated lighting programs is an other possible way of action against T.D. At least, feedstuffs increasing water intake (barley, soja) and poor quality fat or protein sources are responsible wet and greasy capped litters which further the occurence of dermal lesions.