Relationship between Vitamin E and Encephalomalacia in Chicks.

Encephalomalacia is readily produced in chicks by vitamin E-deficient diets containing polyunsaturated fatty acids of the linoleic acid series or their esters (Dam, Nielsen, Prange & Sendergaard, 1958; Century, Honvitt & Bailey, 1959; Machlin & Gordon, 1960). The vitamin is believed to protect against the development of the disease by acting as an antioxidant in vivo, i.e. by preventing the peroxidation of polyunsaturated fatty acids in vital tissues such as the brain. It thus behaves as a biological antioxidant, whereas most synthetic antioxidants inhibit lipid peroxidation in vitro, but display little or no protective activity in the chick. There are few biologically active synthetic antioxidants. Among these may be mentioned 6-ethoxy-I ,2dihydroxy-2,2,4-trimethylquinoline or ethoxyquin (Machlin, Gordon & Meisky, 1959) and N,N'-diphenyl-p-phenylenediamine or DPPD (Bunnell, Matterson, Singsen & Eaton, 1956), only the former being approved in the United States for use in feeding-stuffs. The factors responsible for outbreaks of encephalomalacia under field conditions are much less known, but are generally believed to be similar to those studied experimentally. Thus, added fish oil has often been implicated, since it has been used extensively in the past as a source of vitamin A in feeds. However, there is a surprising dearth of evidence supporting this supposition. Outbreaks of encephalomalacia have been observed regularly in this country, even after fish oil had been replaced by stabilized, fat-free vitamin A concentrates, and in the absence of any fat supplements. The destruction of vitamin E under unsuitable storage conditions of the feed has also been mentioned as a possible causative factor (Winter, 1999, but we have been unable to find any evidence in the literature or from our own observations in the field that such an occurrence has any bearing on the problem of field encep halomalacia. The purpose of our study was to clarify some aspects of the relationship between vitamin E and encephalomalacia on the farm under practical conditions. Two main lines of approach to the problem were used in this work, namely (a) feeding experiments with commercial mashes taken from farms where outbreaks had occurred, or experiments with mashes variously treated so as to lower their vitamin E content or increase the level of fat oxidation products, and (b) assays for vitamin E in mashes and livers of chicks from affected farms and comparison with corresponding values obtained * Contribution from the National and University Institute of Agriculture, Rehovot, Israel. 1962 Series no. 542-E.