New Approaches To Balancing Dairy Cows’ Energy Needs

Energy is often the most-limiting nutrient for the high-producing dairy cow. This is further complicated by the high dry matter intake associated with high levels of milk production. As the cow eats more, the increased rate of passage of feed through the GI tract depresses its digestibility. As a result, the dairy nutritionist is always on the lookout for dense nutrient sources. A good energy option is fat. Dietary fat is a dense energy source, providing 2.25 times the energy of carbohydrate sources.

Fat, however, is not fermented or digested in the rumen. As a result, it cannot replace the need for fermentable carbohydrate as an energy source for the rumen bacteria. Feeding too much can have a negative impact on rumen health causing a depressed intake, reduced milk yield, reduced milk components and reduced fiber digestion. As a general rule of thumb, it is best to keep total fat in the diet below 6% of the total ration with fat divided:

• One-third from basal feed ingredients (forage, most grains, and most grain by-products).

• One-third from added fat (animal fat, whole oil seeds including roasted soy and cottonseed).

• One-third from rumen protected sources (Energy Booster, Megalac, or NutraCor).

When balancing dairy diets we have, however, moved beyond simply balancing for energy or fat. Fatty acids are comprised of a series of carbon-to-carbon bonds with an acid group at one end. The fatty acids in most feedstuffs are made up of carbon chains of up to 18 carbons. Most of the carbons are connected by a single bond, but one or more double bonds are also possible. If the fatty acid contains only single bonds, it is considered “saturated.” With one or more double bonds, it is labeled “unsaturated.” Those with multiple double bonds are identified as being polyunsaturated (PUFA). The greater the number of double bonds, the lower the melting point, with many unsaturated fatty acids liquid at room temperature. As the unsaturation (number of double bonds) increases, so does the negative impact on rumen fermentation. Milk yield and fat percentage are often increased when saturated fat supplements are fed. Increased amounts of unsaturated fats, on the other hand, tend to reduce milk fat percentage.

Fatty acids are identified by the number of carbons and double bonds. C16:0 contains 16 carbons and zero double bonds. A few fatty acids (Figure 1) and their sources are:

C16:0 – Palmitic acid (palm oil distillates)

C18:0 – Stearic acid (hydrogenated tallow)

C18:1 – Oleic acid (canola oil, tallow)

C18:2 – Linoleic acid (corn oil, soybeans, cottonseed)

C18:3 – Linolenic acid (flax, pasture)

The chain length, the number of double bonds, the position of the double bonds and the arrangement of the hydrogen atoms on the carbons involved in the double bonds influence the characteristics of the fatty acid. If the hydrogen atoms around the double bonds are on the same plane, this is known as the cis arrangement. If they are in opposite planes, this is known as the trans arrangement.

In the rumen, bacteria biohydrogenate 18 carbon unsaturated fatty acids to intermediates and, finally, if they stay in the rumen long enough, to stearic acid (C18:0). During this process, hydrogen is added to the double bonds and unsaturated fatty acids are converted to saturated fatty acids. If rumen pH is low, biohydrogenation pathways may become altered, causing unique fatty acid intermediates to accumulate. As little as 1 to 2 grams/day of trans-10, cis 12 conjugated linoleic acid (CLA) may have a significant negative impact on milk fat synthesis.

Research has shown that when palmitic, oleic, and stearic acids were infused, palmitic created the greatest improvement in milk fat production. An additional study has also shown that palmitic acid is absorbed very efficiently by the mammary gland. As a result, Kent Nutrition Group is currently recommending feeding rumen protected fat sources that are high in palmitic acid (Energy Booster hP and NutraCor) as a means of increasing milk fat yield (Figure 2). In response, cows have consistently increased milk fat yield up to 8% or .2 percentage points.

Feeding adequate amounts of energy to the high-producing dairy cow will continue to be a challenge. However, by avoiding over-feeding unsaturated fat, adopting feeding practices that prevent the accumulation of milk fat depressing biohydrogenation intermediates, and feeding sources of rumen protected palmitic acid; it is possible to have both high milk yield and high milk fat.

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