With dermal lesions, bottoms of feet become rough and callused and contain deep fissures that show some hemorrhaging. Foot problems are usually exacerbated by bacterial invasion of lesions. Also, toes may become necrotic and slough off. Tops of feet and legs usually show only a dry scaliness. Lesions appear in the corner of the mouth and slowly spread to the whole area around the beak. Eyelids eventually swell and stick together.
Dermal lesions have a characteristic order of appearance, although speed of onset depends on severity of deficiency. For chicks fed severely biotin-deficient diets, dryness and flakiness of the feet first become noticeable at about 14 days of age, and slight encrustations and superficial fissures develop on the undersurfaces of the feet at about 18 days (Whitehead, 1978). These increase in severity until by about 25 days, the fissures are hemorrhagic. Between three and four weeks, dermatitis may also appear on the eyelids, and as this develops, the bird becomes unable to keep the lids apart, and they eventually stick together.
Dermal lesions are similar to those of pantothenic acid deficiency. However, with biotin deficiency, lesions occur first on feet and later around the beak and eyes, whereas in pantothenic acid deficiency, signs occur first in corners of mouth and eyes and only in prolonged cases appear on the feet. Because of the difficulty of making a differential diagnosis between the two vitamins, it is often necessary to examine the diet composition and decide which is more likely to be deficient. In commercial poultry production both vitamins should be supplemented in a corn-soybean meal ration.
Biotin deficiency is a cause of hock disorders in both poults and chicks. The major deficiency sign affecting market turkeys is severe leg weakness. Lesions caused by biotin deficiency are brought about by chondrodystrophy, a condition in which bone mineralization is normal but linear growth of long bones is impaired. Chondrodystrophy caused by biotin deficiency can result in shortening of metatarsal bones and perosis. Perosis occurs when irregular bone development results in enlargement and deformity of the hock joint (Illus. 5). Crippling in turkeys can occur as early as three to four weeks of age. Often it seems to disappear at six to seven weeks. Then it reappears with great severity between 13 to 16 weeks (Scott, 1981). At this stage the birds are unable to walk and thus can be trampled or cannibalized by other turkeys. Perosis can occur at any stage. In general, young chickens are less susceptible to leg disorders than poults, although biotin deficiency does cause problems of the same type in chicks as in poults (Whitehead, 1978). Once the deformities of perosis occur, biotin administration is not effective.
