As the milk yield and dry matter intake (DMI) of modern dairy cows continue to increase, so too does the amount of fatty acids (FA) reaching the small intestine. Furthermore, supplemental FA are often added to the diet in order to increase the energy density of the ration and support energy requirements of the cow. Thus, the combination of supplemental FA in the diet and increasing DMI causes a significantly higher amount of FA available for absorption in the small intestine. However, previous research has demonstrated that increasing the amount of FA flowing to the small intestine negatively impacts the absorption of FA and thus the amount of energy available to the cow. Our research examined potential strategies to improve FA absorption by utilizing oleic acid (OA) and exogenous emulsifiers. In the first research chapter, we evaluated the effects of varying the ratio of supplemental dietary stearic acid (SA; C18:0) and OA (cis-9 C18:1) on FA digestibility and milk production of post-peak dairy cows. We observed that overall inclusion of supplemental fat increased milk yield, milk fat yield, 3.5% fat-corrected milk, energy-corrected milk, and feed efficiency compared to a non-fat supplemented control. Increasing OA in the supplemental fat treatments increased the digestibility and absorption of FA but did not affect production responses. Our second research chapter examined the effects of increasing doses of OA infused into the abomasum. Increasing the amount of OA reaching the duodenum did not affect DMI but increased the digestibility and absorption of total, 16-carbon, and 18-carbon FA. Higher absorbed FA increased plasma insulin, but did not affect BW or BCS, and tended to increase milk yield, 3.5% FCM, and ECM. In the third research chapter, we abomasally infused 30 g/d of three exogenous emulsifiers (Tween) that differed in the FA attached to the polysorbate base. Compared to control, the overall effect of Tween did not affect DM intake or digestibility, but increased milk fat content and tended to increase milk fat yield and 3.5% FCM. The emulsifier containing OA, Tween80, improved digestibility of 16-carbon, 18-carbon, and total FA compared to control and to the two other emulsifier treatments. Tween80 also increased milk fat content and yield compared to control. Thus, Tween80 has the potential to improve nutrient digestibility and milk production, but it is unknown whether this is primarily due to the polysorbate or the attached OA. Our last research chapter directly compared abomasal infusions of OA and Tween80, as well as examined the interaction between the two. OA increased the absorption of total and 18-carbon FA but had negligible effects on production responses. Tween80 did not affect nutrient digestibility but increased milk yield, decreased milk fat content, and did not affect milk fat yield. These results contradict previous research utilizing Tween80, but the reason for this is unclear as energy status and FA intake was similar across studies. No interactions between OA and Tween80 were observed for nutrient digestibility but an interaction was observed for ECM, milk fat yield, feed efficiency, and BCS. Overall, there is evidence that both OA and Tween80 can improve FA digestibility. When directly compared, OA was more beneficial to total, 16-carbon, and 18-carbon FA digestibility than Tween80 and providing both had no additional benefits. Therefore, increasing the amount of OA reaching the small intestine is a viable strategy to improve FA digestibility and thus energy availability to the cow. Exogenous emulsifiers can also improve FA digestibility, but results are inconsistent and should be investigated further in the future. Furthermore, combinations of OA and various emulsifiers should be further examined for independent and interactive effects.
Read
