The effect of the type of roughage in the diet on plasma cholesterol levels and aortic atherosis in rabbits

1. Eleven groups of male rabbits (eight to eleven per group) were given ad lib. a diet consisting of 61 parts of a low-fat basal ration to which were added: for groups 1–3, 20 parts maize oil; for groups 4–7, 20 parts butterfat; and for groups 8–11, 0.47 parts maize oil and 43.1 parts wheat starch. Different types of roughage were added to the 61 parts of basal ration as follows: for groups 1, 4 and 8, 19 parts ground wheat straw; for groups 2, 5 and 9, 19 parts Solkafioc; for groups 3, 6 and 10, 19 parts of shredded cellophane; and for groups 7 and 11, 14 parts shredded cellophane and 5 parts peat.2. After the rabbits had been given the experimental diets for a period of 40 weeks, the plasma cholesterol levels were determined. The animals were then killed and the degree of atheromatous degeneration was determined after the aortas had been stained with Sudan IV.3. Elevated levels of plasma cholesterol and extensive atheromatous degeneration were observed in the rabbits given the diets containing 20% butterfat (groups 4–7) and in those given the diets containing 48% starch (groups 8–11). Lower levels of plasma cholesterol and only slight atheromatous degeneration were observed in the rabbits given the diets containing 20% maize oil (groups 1–3).4. The levels of plasma cholesterol and the degree of aortic atherosis were influenced very markedly by the nature of the dietary roughage. Plasma cholesterol levels and degrees of aortic atherosis tended to be higher when cellophane was the roughage component than when wheat straw was the roughage component of the diet. The replacement of part of the cellophane of the diet by peat reduced the level of plasma cholesterol and the degree of aortic atherosis.5. The possible mechanisms by which the nature of the dietary roughage influences plasma cholesterol levels are discussed.