STUDIES ON PARAKERATOSIS IN SWINE

rarely resulted in mortality. The condition has appeared most often in pigs from 10 to 16 weeks of age and has been almost completely limited to fall-winter feeding trials. Although pigs with severe symptoms of parakeratosis have had sig- nificantly lower levels of serum vitamin A than normal animals, oral therapy with massive doses of vitamin A acetate has been of no ap- parent benefit to improvement either of disease conditions or of serum vitamin A level. Whether avitaminosis A was due to depressed food consumption or failure to absorb vitamin A from the digestive tract was not determined. Attempts to alter the course of parakeratosis by changes in quality of dietary protein were also ineffective. The association between high calcium content in swine diets and in- tensified symptoms of parakeratosis was reported by Ellis (1953). Results of this experiment, which was designed to investigate a "rickets- t Animal and Poultry Husbandry Research Branch, Agricultural Research Service, Agricultural