J. R. Loften , J. G. Linn , J. K. Drackley , T. C. Jenkins , C. G. Soderholm , and A. F. Kertz
Energy is and will continue to be the major nutritional challenge to the ever-increasing lactation productivity of dairy cows. Because of this, dairy producers and nutritionists have increased the use of high-energy feed ingredients, such as fat, in lactating dairy cow diets. Dry, ruminally inert fat supplements have become common feed ingredients in diets because of their energy content and versatility on farms, where they can be added to grain mixes, mineral mixes, total mixed rations, or top dressed. Dry rumen-inert fats usually contain high concentrations of long-chain fatty acids, with the most common being palmitic (C16:0), stearic (C18:0), oleic (C18:1), and linoleic (C18:2). Research over the last several years has shown fatty acids are not just a ubiquitous source of energy, but have metabolically different functions in the cow and contribute to the productive function of cows in different ways. This paper discusses the roles of C16:0 and C18:0, the 2 most common saturated fatty acids found in rumen inert fats, in the metabolism and productivity of lactating dairy cows.