Feeding Fat to Dairy Cows

Dairy cows need a tremendous amount of energy; a dairy cow weighing 1,400 lb and producing 70 lb/day of milk with 3.6% fat and 3.3% protein needs about 33 Mcal/day of net energy for lactation (NE_L). Although the units are somewhat different, this is about 26 times more energy than for a person consuming a recommended 2,000-calorie diet. Concentrates are higher in energy density than forages, but adequate dietary effective fiber is needed to maintain rumen function, so concentrates need to be limited in the diet. Thus, one of the primary purposes of feeding supplemental fat to dairy cows is to increase energy intake. Fats are higher in energy density than carbohydrates and proteins; therefore, adding fat increases the energy density of the diet. At the same time, feed intake must be maintained; otherwise, an increase in energy intake may not occur. Feeding excessive amounts, especially unsaturated fat, can reduce feed intake and occasionally energy intake.

The most common whole oilseeds fed to dairy cows are soybeans and cottonseeds. Because of the value of the oils, the whole seeds of canola, linseed, safflower, and sunflower are not typically fed, but the respective meals that result after the oil is extracted are commonly fed. The amount of oil remaining in some of these meals can be an important contributor to the total amount of fat in the diet. In addition, several plant and animal by-products, such as distiller’s grains (high and low fat available), hominy, fish meal, and meat and bone meal, may contain 10% to 12% fat. Fish meal is fed primarily as a high-quality, rumen-undegradable protein source, and the fatty acid (FA) composition is distinctive, with about 24% of the fat being unsaturated FA with 20 or more carbons. Feeding grease, lard, or tallow requires these fats to be heated for transport, storage, and mixing. Thus, special storage and handling equipment is needed. The costs of this equipment and the handling of liquid feed are deterrents for some producers who blend these sources of fat in diets on the farm.

Several commercial sources of fat are available that are rumen inert ( do not cause reduction of fiber digestibility in the rumen), while some are designed to deliver specific FA to the cow. Most of these are in the form of calcium salts of FA or highly saturated FA. The calcium salt products usually are from palm oil (high in palmitic acid; C16:0) or other plant sources (e.g., soybean) and are in granular form. The highly saturated FA sources are processed into very small beads (prills), much like in a powder form, to aid in digestibility and handling. Some of the commercial fat products are developed to deliver higher amounts of C16:0 to the cows for possibly increasing milk fat yield given that milk has a relative high concentration of C16:0, and C16:0 may be more digestible than C18:0. Other fat sources are enriched in omega-3 FA (usually from aquatic sources or linseed) which may positively influence reproductive and immune function.