Comparison of the activities of the acetates of d-, d,l- and l-α-tocopherols against encephalomalacia in chicks

The activities of the acetates of d-, d, l- and l-α-tocopherols against encephalomalacia in chicks reared on a diet with 30% lard as the main source of linoleic acid and 31.53% corn starch as source of carbohydrate were found to be 168 for the d-form, 100 for the d,l-form, and 44 for the l-form (the activity of d, l-α-tocopherol acetate arbitrarily being set at 100). The accuracy of the determinations is not very great. It could be increased by using more chicks for the doses giving an incidence of encephalomalacia of about 50%, and smaller intervals between the doses. Full protection against encephalomalacia was obtained with 1.19 mg% of the d-form, 2.00 mg% of the d,l-form, and 4.52 mg% of the l-form, all as the acetates. Assuming that the free tocopherols have the same activity as their acetates on a molar basis, full protection would be reached with 1.08 mg% of the d-form, 1.82 mg% of the d, l-form, and 4.12 mg% of the l-form, all as the free tocopherols. Analysis of the lard and corn starch used in the experiments showed that the diet with 30% lard contained 1.57% linoleic acid, viz. 1.50% from lard and 0.07% from corn starch. Further, the diet contained 0.17 mg% d-α-tocopherol originating from lard. The content of d-α-tocopherol originating from corn starch was negligible. From the above mentioned data it can be calculated that a total amount of 1.25 mg d-α-tocopherol was required for compensation of the encephalomalacia producing effect of 1.57 g of linoleic acid under the conditions of the experiment.