Abstract: A rumen by-pass feed supplement in the form of a matrix containing up to about 70 percent by weight of at least one biologically active material susceptible to inactivation in the rumen, and a protective substance which is a glyceride-free mixture of aliphatic fatty acids having an Iodine Value between 10 and 20, in an amount effective to both form a fatty acid matrix with the biologically active material and a surface coating impervious to attack in the rumen. Ruminant feeds containing the rumen by-pass feed supplements are also disclosed, as well as processes for supplying the rumen by-pass feed supplements to ruminant animals.