Vitamin A deficiency in chickens.

The importance of vitamin A for the normal development and maintenance of skeletal, nervous and epithelial tissues has long been recognized, and the general signs of deficiency of this vitamin in chickens have been described by Seifried (1930) and by Beach (1923). One of the most important changes caused by vitamin A deficiency, often leading to serious infection, is the replacement of many secretory epithelia by non-secretory, keratinizing membranes. In the experiments reported here, the effects of vitamin A deficiency on the corneal, conjunctival, oesophageal and tracheal epithelia of the young chick have been studied. In many animals these epithelia show metaplastic changes in vitamin A deficiency. Xerophthalmia (i.e. drying of the eyes, with keratinization of the corneal and conjunctival epithelia) was one of the first signs recognized as characteristic of vitamin A deficiency, and in many species, e.g. the rat, it is often one of the earliest and most obvious changes to appear. In vitamin A-deficient chickens, gross changes can be seen in the eyes (Beach, 1923), but these lesions are not as extensive or as obvious as they sometimes are in rats and many other mammals. Metaplastic changes also occur in the mucous glands of the chick oesophagus in vitamin A deficiency (Beach, 1923; Seifried, 1930); in the trachea the epithelium, which is normally ciliated and secretory, gradually becomes stratified and keratinized (Seifried, 1930). It was thought desirable to study the effects of vitamin A deficiency on these epithelia in more detail, however, for comparison with changes in the same tissues grown as organ cultures and subjected to varying concentrations of vitamin A. The results of these tissue-culture experiments, and a comparison between the epithelial changes observed in vitro and in vitamin A-deficient chicks, are presented in another publication (Aydelotte, 1963).