HIGH PURITY FAT SUPPLEMENTS AND THEIR IMPACT ON DIGESTIBILITY
Posted by Richard Shepardson, M.S. and Matthew Sellers, Ph.D on Sep 13, 2020 4:30:00 PM
Commercial fat supplements for dairy cows containing varying ratios of palmitic (PA; C16:0), stearic (SA; C18:0), and oleic acids (OA; C18:1) are common in modern lactating dairy rations. Some commercial supplements contain a blend of multiple fatty acids (e.g. PA + OA, PA + SA), whereas other supplements may be highly enriched in just a single fatty acid (FA). The profile of a supplement largely impacts FA digestibility. Recent research reports that supplemental fats that are highly enriched (>90%) in either PA or SA have very low digestibility compared to supplements that are of moderate (~80-85%) or low enrichment (<60% of a particular FA). When choosing a supplemental fat feeding strategy, FA profile should be taken into account in order to maintain adequate digestibility and thereby maximize return on investment.
MODERN OPTIONS FOR FATTY ACID SUPPLEMENTATION
The market is full of name-brand and generic supplemental fat options with a wide range of FA profiles. Common options include prilled fats (i.e. palmitic acid prills, Energy Booster 100™, etc.), calcium salts of palm FA distillate, tallow, and many others. Both PA and SA are saturated FA, meaning that the hydrocarbon chain on the FA does not have any double bonds (hence the “0” in C16:0 and C18:0), whereas unsaturated fats such as OA have one or more double bond. Prilled fat supplements sold in the dairy industry are available with a large variety of FA profiles, particularly in regard to PA and SA content. Some fat supplements are highly enriched in a single FA (>90%), some are moderately enriched in a single FA (~80-85%), and others are blended fats with low enrichment typically containing 60% or less of any one FA and may have two or three featured in their profile.
IMPACT OF SUPPLEMENT PROFILE ON FATTY ACID DIGESTIBILITY
The profile and quantity of FA reaching the small intestine has a significant effect on apparent FA digestibility. A recent meta-analysis by Boerman et al. (2015) reported that increasing total FA in dairy rations decreases total FA digestibility but increasing unsaturated FA flow to the small intestine may help improve absorption. It is important to remember that the majority of all dietary unsaturated FA are biohydrogenated to SA in the rumen, making SA the most abundant FA in the small intestine. Fat supplements must be well absorbed by the cow in order to maximize efficiency and return on investment. Although supplementing unsaturated FA such as OA may slightly improve FA digestibility relative to PA or SA, feeding large amounts of unsaturated FA can decrease DMI and negatively affect rumen function. To avoid the negative effects of unsaturated FA, many popular fat supplements predominantly feature PA, SA, or a combination of both.
Recent publications have evaluated the effects of fat supplements with varying enrichment of PA or SA on FA digestibility. A recent meta-analysis by Daley et al. (2020) found that supplements that are >90% enriched in either PA or SA have much lower digestibility than supplements with low or moderate enrichment (~80-85%). Piantoni et al. (2013) fed lactating cows a 99% PA supplement at 2% of diet DM and decreased C16 FA digestibility 17.5 percentage units relative to control. Piantoni et al. (2015) fed a 98% SA supplement at 2% diet DM and decreased C18 digestibility 23.8 percentage units compared to a non-supplemented control ration. An experiment by Boerman et al. (2017) utilized a 93% SA supplement that yielded similar results. In contrast, other publications have utilized supplements with 80-88% enrichment of PA at 1.5-2% of diet DM and reported more moderate decreases (5-10 percentage units) in C16 digestibility (de Souza et al., 2017; de Souza and Lock, 2018) Another publication reported cows supplemented with an 84% PA supplement at 1.9% diet DM had slightly increased C16 FA digestibility (Rico et al., 2014). Harvatine and Allen (2006) fed a supplement containing both PA+SA and total FA digestibility was only moderately decreased by 6.2 percentage units.
For supplemental fat to be available for use by the cow, it must be hydrolyzed into free FA, emulsified, and absorbed in the small intestine. Emulsification is a key step, as lipids are incorporated into micelle structures and then absorbed through the lining of the small intestine. If lipids cannot be emulsified, they cannot be absorbed and therefore cannot be utilized by the dairy cow for maintenance, growth, lactation, or reproduction. It is apparent that blending FA together in a prilled fat improves FA digestibility compared to feeding a highly enriched (>90%) PA or SA supplement.
Saturated FA are capable of forming crystalline structures, particularly when in purified form. These lipids have a polar head with a nonpolar hydrocarbon chain, and the configuration of these molecules allows them to stack upon each other to form rigid crystalline structures similar to a stack of uniform bricks or logs. When a different FA is incorporated even at modest levels, the structures formed are not as large or rigid. Unsaturated FA such as OA, which have bent hydrocarbon chains, can greatly reduce the size and rigidity of the crystalline structures. Where a high purity PA or SA supplement could be compared to a uniform stack of bricks or logs, a supplement containing multiple different saturated and unsaturated FA is analogous to a mixed pile of bricks, logs, and hockey sticks – no matter how hard you try, it cannot be stacked well. A recent publication by Shepardson et al. (2020) found that fat supplements that were >95% PA or SA had much higher melting temperature and enthalpy values (energy required to melt a sample) than supplements that had inclusion of a second FA. Even just ~4% OA added in to a 93% PA supplement altered the physical characteristics of the supplement by lowering the melting temperature and enthalpy values. This suggests that the physical properties of highly enriched FA supplements may be more difficult to emulsify in the small intestine due to their rigid crystalline structures compared to supplements that are more moderately enriched, but more research is needed in this area.
IMPACT OF SUPPLEMENT PROFILE ON FATTY ACID DIGESTIBILITY
There are many fat supplements for lactating dairy cattle on the market based on varying contents of PA, SA, and OA. Fat supplements that are >90% pure in either PA or SA have poor digestibility compared to those of more moderate enrichment (~80-85%). This may be due, in part, to the physical properties of saturated FA, as they form secondary crystalline structures in high purity that result in increased melting temperature and enthalpy values compared to blends of FA. Feeding fat supplements that are of moderate enrichment or blends of FA may be helpful in improving FA digestibility in lactating dairy cows.
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Topics: ANIMAL NUTRITION