The Pathology of Pyridoxine Deficiency in Chicks

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Abstract
White Plymouth Rock × Vantress chicks were fed a high protein (31%) purified diet based on isolated soybean protein. This diet was complete in all required nutrients except for pyridoxine, which was fed at graded levels ranging from 1.9 to 4.9 mg/kilogram of diet. Chicks receiving the basal diet (1.9 mg pyridoxine/kg) and those receiving 2.2 mg B6/kilogram of diet grew very poorly, showed severe nervous signs and died within 6 to 10 days. No pathological lesions were found. Chicks receiving 2.5 mg B6/kilogram of diet grew at a subnormal rate, did not develop nervous signs, but showed severe perosis (80% incidence) and were moribund by 4 weeks of age. Epiphyseal lesions consisted of an uneven invasion by irregularly shaped blood vessels into a disorganized vesicular zone of the maturing growth plate. The consequent distortion of the epiphyseal cartilage caused bone curvature which resulted in perosis. Chicks receiving 2.8 mg B6/kilogram of diet had a 20% incidence of perosis of a milder nature and grew significantly better than the chicks receiving 2.5 mg pyridoxine/kilogram of diet. Although growth was reduced in comparison to the controls, the chicks receiving 3.1 mg B6/kilogram of diet had no clinical perosis, and only mild microscopic epiphyseal lesions were found. All higher levels of vitamin B6 produced growth approximately equal to that of chicks on the positive control ration containing 7.1 mg pyridoxine/kilogram of diet on an ad libitum basis. Chicks fed the control diet (31% protein with 7.1 mg pyridoxine/kilogram of diet) at restricted levels equivalent to the intake of the chicks receiving 2.2, 2.5 and 2.8 mg pyridoxine per kilogram of diet, showed no histological lesions or clinical signs other than lower rates of growth commensurate with the restriction of feed intake. Chicks fed a normal protein diet (22% protein) without added pyridoxine (1.4 mg pyridoxine was present per kilogram of this lower protein basal diet) showed no nervous signs or perosis, no pathological lesions were found, and the chicks grew as well as those receiving the positive control diets containing 31% protein and 7.1 mg pyridoxine/kilogram of diet. These experiments demonstrate that the pyridoxine requirement of chicks receiving normal protein diets is very low, but that the requirement is increased markedly when the diet contains excess protein. One of the signs of a borderline deficiency of pyridoxine is severe perosis.