THERE seems to be a significant relationship between serum cholesterol concentrations and the incidence of atherosclerosis in man1–4. In the past, considerable attention has been focused on the possible relationships between the consumption of ruminant products (for example, lamb, beef, milk, butter, cheese and cream), high concentrations of serum cholesterol and coronary heart disease in man5. These relationships have been attributed largely to the relatively high proportions of saturated fatty acids that occur in ruminant fats, and the possible role of these fatty acids in increasing serum cholesterol concentrations6,7. Moreover, it is now firmly established that the substitution of poly-unsaturated fats for saturated fats in human diets will cause a reduction in the concentration of serum cholesterol5–10. For these reasons, ruminant fats are largely excluded from the diets of patients being treated for coronary heart disease5,11. The availability of poly-unsaturated ruminant products would therefore assist in the formulation of special diets for experimental work and for therapeutic use in patients with atherosclerosis.