Young Scholar Presentation: Altering the Dietary Ratio of Fatty Acids Under Different Physiological Conditions on Energy Partitioning of Dairy Cows

Our research examined the effects of varying the dietary ratio of fatty acids (FA) under different physiological conditions on nutrient digestion, energy partitioning, and production responses of dairy cows. We evaluated the effects of varying the ratio of dietary palmitic (C16:0), stearic (C18:0), and oleic (cis-9 C18:1) acids on post-peak dairy cows. Among the combinations of C16:0, C18:0, and cis-9 C18:1 evaluated, FA supplements with more C16:0 increased energy output in milk, whereas FA supplements with more cis-9 C18:1 increased energy storage in body reserves. Increasing C18:0 in a FA supplement reduced FA digestibility and did not increase energy intake, which most likely explains its lower performance compared with the other FA treatments. Based on the aforementioned results, we evaluated the long-term effects of C16:0 supplementation on primiparous and multiparous post-peak dairy cows. Our results demonstrated that supplementation with C16:0 consistently increased DMI, milk yield, milk fat content and yield, energy-corrected milk, and NDF digestibility in both multiparous and primiparous cows. In addition, C16:0 supplementation increased body weight (BW) change in primiparous cows but not in multiparous cows. Furthermore, we determined the effects of timing of C16:0 supplementation on production and metabolic responses of early lactation dairy cows. Our results suggest that feeding a C16:0 supplement to early lactation cows consistently increased the yield of energy-corrected milk compared with a non-fat control diet regardless of the timing of supplementation. C16:0 supplementation also increased NDF digestibility, energy intake, and milk energy output. When fed immediately postpartum, C16:0 increased negative energy balance and plasma non-esterified FA, increased BW and BCS loss, and decreased plasma insulin. Finally, we evaluated responses of lactating dairy cows with different levels of milk production to alterations to the dietary ratio of C16:0 and cis-9 C18:1. Our results indicated that high producing dairy cows (averaging 60 kg/d) respond better to FA supplements containing more cis-9 C18:1, while lower producing cows (averaging 45 kg/d) respond better to supplements containing more C16:0. Regardless of production level, increasing cis-9 C18:1 increased total FA digestibility, BW and BCS change, with no effect on DMI. Overall, our results indicated that altering the dietary ratio of C16:0 and cis-9 C18:1 may change energy partitioning in dairy cows and the magnitude of response is associated with the physiological state.