Breeding, Growth and Resistance to Infection of Mice Fed on Six Natural Diets

In their comprehensive review, ' Influence of nutrition in experimental infection ', Clark, McClung, Pinkerton, Price, Schneider & Trager (1949) noted that 'the great diversity of the experiments and the not infrequent inadequacy of controls, present such confusing and at times conflicting results that any attempt to generalize would seem premature'.They concluded that: 'Further efforts to unravel the snarled skein should continue.'This is a good summary of the present position.In a series of valuable experiments Schneider (1948) defined a suitable technique for studying the influence of diet on salmonella infection of mice.He found (Schneider, 1949) that whole wheat contained a substance that he termed 'the mouse-salmonellosis resistance factor'.By fractionation studies he found that this factor was concentrated in wheat germ and began work for its isolation and characterization.Another approach was indicated by Howie (1948-9), who proposed to test the resistance to infection of young mice born of parents fed on natural diets and mated continuously in order that this stress might reveal possible dietary imperfections, as described by Bruce & Emmens (1948).In accordance with this plan the work described here was undertaken to see whether the resistance to infection of animals fed on a particular diet was correlated with the value of the diet as judged by its capacity to support reproduction and growth.Sengupta & Howie (I 948-9) described differences in the resistance to experimental tuberculosis of mice bred and reared on two diets of natural food (diets I and 2).These differences, though not great, were statistically significant.It seemed useful to attempt to increase the differences in resistance by modifying the diets; this paper gives the results of attempts to do this. METHODS Mice.The mice employed were albinos of the W-Swiss strain bred in the Institute colony, whose origin was described by Sengupta & Howie (19483).Mating procedures.The system of monogamously mated pairs described by Bruce & Emmens (1948) was used in these experiments.All the parent mice for the experiment were born between 21 and 29 July 1948.They were born of animals fed on diet 3 (see below) and were themselves fed on diet I (see below) until given the appropriate experimental diet, numbered I , 2 , 3 , 4 , 5 or 24 (see below).The feeding of the experimental diets was begun when the pairs were mated on 4 October 1948, i.e. when they husbandry, i.e. not a 'synthetic' or chemically defined diet.As used in this paper the term 'natural diet' means a diet of foodstuffs commonly used in animal ~1 ~2 .