Further studies of the rachitogenic effect of dried yeast in pig diets.

In previous papers Braude, Kon & White (1943, 1944) described the development of rickets in fattening pigs on diets containing a large proportion of yeast, its cure or complete prevention with vitamin D, and its partial prevention with additional calcium salts. The yeast was added as a protein supplement to normal fattening rations to the extent of &zo%. The cause of the rickets remained obscure, though it was unlikely (Braude et al. 1944) that it was due to the high phosphorus content of the yeast. The present paper describes further attempts to determine the nature of the rachitogenic factor, some of them, including a test of stability of the factor to heat, made some time ago, others recent, dealing with the possible connexion between the rachitogenic effect and the phytate phosphorus content of the diet. Practical rations for pigs, because of their high cereal content, are relatively rich in phytic acid; this is normally hydrolysed in the gut by the phytase present in the majority of cereals (Pedersen, 1940; Mollgaard, 1946). It seemed possible that yeast might in some way inhibit the hydrolysis of phytic acid in the diet and that this would affect the availability to the pig of calcium and phosphorus and lead to rickets. Experiments were therefore planned to test this point. In the meantime Hoff-Jsrgensen (1947) published results of experiments in vitro supporting the view that brewer’s yeast inhibited phytase activity.