Rapid growth dairy heifers having reduced mammary fat content

The present invention provides a feedstock for intensive feeding of replacement dairy heifers to promote rapid growth, and facilitate early breeding and first calving at an age of about 20-24 months. The calved heifers subsequently yield increased first lactation milk production and lifetime milk. An essential ingredient of the invention feedstock is conjugated linoleic acid derivative having remen-bypass properties. The quantity of conjugated linoleic acid derivative is effective for prevention of mammary gland tissue damage by minimizing mammary fat content. A preferred feedstock includes a content of slow-release degradable nitrogen source for efficient rumen fermentation, and a content of rumen-bypass protein.