Evaluation of Dairy Ultra 100
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Contents
- Introduction
- Fat Digestibility
- Rumen Inertness
- Palatability
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This discussion is aimed at clarifying what's known about fat digestion, absorption and metabolism, and how the various forms of rumen inertfat, including Dairy Ultra 100, fit into this picture. The following discussions are matter-of-fact presentations of factors affecting the relative value of supplemental fats in dairy rations.
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Fat Digestibility
The Net Energy (NEl) value presented for most fats is the result of a mathematical calculation based on the digestibility of the fat. Digestibilities are determined through research trials, and are then plugged into the NEl formula. The higher the digestibility value, the higher the NEl. Digestibility trials usually estimate digestion coefficients by evaluating the difference between fat-supplemented and nonsupplemented diets. The general assumption is that factors other than digestibility differences do not influence results.
However, many factors influence fat digestibility and metabolism including genetics, energy status of the animal, composition of the basal ration, feed intake and amount of supplemental fat. The effect of non-measured influences is evident in the wide variation of digestibilities determined in research trials. For example, digestibilities for calcium salts of palm oil vary by about 40 percentage points. Wide variation are also seen in digestibilities of other supplemental fats. Obviously it is wrong to compare digestibilities of different fats determined through different trials.
One method of reducing variability is to evaluate digestibilities of different fats within a single study. The table below lists the results of several of these studies. The data indicate that the relative performance offats within a study is not as varied as individual studies suggest, and that the true digestibility and NEl ofa fat are not as high as the values presented by manufacturers.
If NEl values are being used in ration balancing programs more realistic NEl values should be calculated based on more reasonable digestibilities. At the very least, NEl values should be adjusted downward. Due to the large variation in fat digestibilities, there is no clear-cut way of knowing how close the presumed digestibility of a fat will be to its true digestibility in any one ration.
Fatty Acid Profiles. It is fairly well substantiated in both ruminants and nonruminants that unsaturated fatty acids are more readily digested than saturated fatty acids. Human research with fatty acid markers enable researchers to track the absorption and metabolism of specific fatty acids in a test diet. In ruminants, no such markers are used. Consequently there is no way of knowing whether specific fatty acids are from the test fat, the basal diet, or if they were produced and/or modified by rumen bacteria.
In marker trials evaluating absorption and metabolism of 3 fatty acids commonly found in human diets, the unsaturated fatty acid, oleic (C18:1), shows consistently high absorption levels in the small intestine (approximately 98%). The saturated fatty acids, palmitic (C16:0) and stearic (C18:0), generally show lower absorption levels. Although trials have shown palmitic and stearic acid absorption to be similar (around 85%), modifications to the fatty acid suspension medium has resulted in palmitic acid absorption of nearly 99% and stearic acid absorption of 91%. Absorption of stearic acid appears to be the most variable of the fatty acids and tends to be equal to or lower than other saturated fatty acids. Since digestion and absorption of fatty acids in the small intestines of ruminants and nonruminants is similar, we would expect similar digestibility results. Ruminant research appears to support these findings. Considering the form and fatty acid profiles of different supplemental fats along with digestibility evidence, the ranking of different types of fat supplements according to overall digestibilities would be:
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Rumen Inertness
Rumen inertness is used to describe supplemental fats which do not significantly alter rumen function when fed at the recommended level. Although the term "by-pass" is used by some manufacturers, it is inappropriate since it does not reflect what actually happens in the rumen. Supplemental fats affect rumen function in several ways: triglycerides tend to be hydrolyzed by rumen microbes into free fatty acids and glycerol; rumen microbes tend to biohydrogenate, or convert unsaturated free fatty acids into saturated fatty acids; and fats may directly affect fiber digestion. These characteristics are affected by the form in which the fat is fed. Calcium salts of palm oil appear to be better protected from biohydrogenation than free fatty acids of tallow. Tallow tends to be hydrolyzed to free fatty acids, and then subjected to biohydrogenation. Prilled tallow has a higher melting point than the other supplemental fats and remains solid in the rumen environment, reducing microbial interaction. This isolated nature of prilled tallow may impart a high level of rumen inertness, but could be a factor in its somewhat lower digestibility in the small intestine. Although there is some uncertainty as to whether prilled tallow is first or second in rumen inertness, the following hierarchy should provide a fair representation of what is currently known about rumen inertness:
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Palatability
Effects of palatability differences of supplemental fats on feed intake and performance are not well researched and their relationship to feed intake is often overlooked. The palatability and aroma of calcium salts and free fatty acids are such that they must be hidden in the ration. This is not the case with Dairy Ultra 100. Strict interpretation of digestibility research suggests that performance results with prilled tallow will be consistently lower than calcium salts, free fatty acids and tallow. Since these lowered expectations are not realized in actual applications, something else must be going on. Assuming digestibility research is correct, it is quite likely that the good taste and aroma of Dairy Ultra 100 encourages cows to eat, resulting in better performance. Top-dressing Dairy Ultra 100, especially after cows have finished eating and are turning away from the feed, is a sure way to test their reaction. Supplemental fat palatability can be ranked as follows:
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