Effects Of Nutritional Supplementation Of Palmitic And Stearic Acid On Milk Composition And Milk Fat Globule Membrane In Multiparous Holstein Dairy Cows And Primiparous Brown Swiss Cows PDF Download

Energy in many modern lactating dairy cow rations is a limiting factor for production. Supplementing diets with various fat sources can improve energy intake, which allows cows to maintain milk and component production as well as body condition. Due to the negative effects on intake and rumen fermentation by unsaturated fatty acids (UFA), many modern supplements are based on saturated long chain fatty acids (FA), which are not expected to cause adverse effects in the rumen. These supplements are commonly based on palmitic acid (PA) and stearic acid (SA), as well as various combinations thereof. First, this thesis investigated the physical characteristics of fat supplements and FA stocks (often used for making FA blends for commercial products). Supplements that are highly enriched (>95%) in PA or SA tend to have lower digestibility than those that are moderately enriched (~85%) or are a blend of PA and SA. Lipids have the ability to form rigid, secondary crystalline structures and this thesis provided evidence using differential scanning calorimetry (DSC) that increasing the enrichment of a FA within a fat supplement increased both the melting temperature and the amount of energy (enthalpy) required to melt a sample. Increasing UFA in FA stocks also decreased both melting temperature and enthalpy compared to enriched FA stocks. This is indicative of the formation of secondary crystalline structures and suggests that these physical characteristics may be playing a role in the decreased digestibility of highly enriched supplements. Secondly, this thesis conducted an experiment with lactating cows comparing supplements that differed in FA profile and demonstrated that fat supplements that were ~90% PA and approximately a 50/50 blend of PA and SA improved milk fat production compared to a supplement that was ~90% SA and a no-supplemental fat control group. The PA/SA blend also improved energy corrected milk compared to the SA treatment. Fatty acid digestibility was decreased with increasing inclusion of SA in the diet, which may have been an issue of either exceeding the lower tracts ability to emulsify the extra saturated long chain FA or that the supplement prill was not easily broken down. Thirdly, a subsequent experiment with lactating cows observed that increased inclusion of oleic acid (OA) in a supplement of mostly PA and SA did not change milk or component production in any facet. There also was no milk production response to lecithin being directly incorporated into the supplement. However, digestibility data will be necessary to assess whether or not these potential emulsifiers improved FA absorption in the lower tract. In conclusion, this thesis presents a potential tool for screening fat supplements for secondary physical characteristics via DSC. It also presents data that suggests PA improves production and FA digestibility compared to SA, and finally that increasing OA and lecithin do not have appreciable impacts on milk and component production.