A feed composition for ruminants comprising a microbe having nitrite reductase activity, wherein said microbe has been modified so that intracellular nitrite reductase activity is enhanced is disclosed. A feed composition for ruminants comprising a microbe having nitrite reductase activity, wherein said microbe is selected from the group consisting of intestinal bacteria, coryneform bacteria, Bacillus subtilis, bacteria of the genus Methylophilus, Actinomyces, ruminal bacteria, and a combination thereof is disclosed. A method of improving the growth of a ruminant by administering the feed composition as described above to said ruminant and a method of preventing nitrite intoxication by administering the feed composition as described above to a ruminant are disclosed.