Heat stressed dairy cows typically have reduced dry matter intake (DMI) and milk production making them less profitable. Fatty acid (FA) supplements are sometimes used to mitigate heat stress. We hypothesized that feeding a FA supplement of 59% palmitic and 29% oleic acids would improve milk production during summer months. We conducted 2 studies to test this hypothesis. Study 1 was conducted in the summer of 2022 using 40 Holstein cows (95±38 DIM; mean ± standard deviation; 47±10 kg milk/d; and 646±88 kg BW, 12 were primiparous), and Study 2 was conducted in the summer of 2023 using 41 Holstein cows (93±38 DIM; 46±11 kg milk/d; 694±114 kg BW; 17 were primiparous). Cows were fed a common diet for a 6 wk preliminary period, blocked by parity, days in milk, and energy corrected milk/metabolic body weight, and randomly assigned to a control (CON) or fat supplemented (FAT) diet. In both studies, CON and FAT diets were corn silage based and contained ~20% forage NDF and 17% CP. The FAT diet contained an additional 1.23% PA and 0.61% OA as a Ca-salt. The FAT diet increased yields of milk fat 0.07 kg/d, energy-corrected milk 1.6 kg/d, and tended to increase milk yield 1.2 kg/d compared to CON. The FAT diet did not affect DMI, yields of milk protein or lactose, or body weight. The FAT diet increased yields of milk FA of >16 carbon and 16 carbon while decreasing milk FA <16 carbons as well as increasing plasma NEFA concentration. In conclusion, feeding a supplemental FA containing 59% palmitic and 29% oleic FA at 2.09% of diet DM to dairy cows improved milk production 2.9% during warm weather.
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