The effect of increasing dietary palmitic and stearic acid on melting properties of milk fat from Holstein cows.

Palmitic and stearic acid are commonly fed to dairy cows but limited data are available on their effects on thermal properties of milk fat, especially when fed at different levels. Recently, some consumers voiced concerns about butter being harder at room temperature and questioned if it was caused by palmitic acid supplementation of dairy cows. Our hypothesis was that increasing palmitic acid intake would linearly increase palmitic acid in milk fat and, therefore, increase the solid fat content (SFC) of milk fat at 20°C, whereas increasing stearic acid intake would increase both stearic and oleic acid in milk fat and not change the SFC of milk fat at 20°C. A total of 12 second-lactation Holstein cows (106 ± 31 DIM) were arranged in a replicated 3 × 3 Latin square design with a dose escalation design within period and ≥10 d washouts between periods. Treatments included a no-supplement fat control (CON), a fatty acid (FA) supplement high in palmitic acid (PA; 88% palmitic and 8% oleic), and a FA supplement high in stearic acid (SA; 81% stearic and 10% oleic). The FA supplements were fed at increasing doses every 4 d, targeting 150, 300, 500, and 750 g/d. Milk samples were collected on d 3 and 4 of each dose, composited, and milk fat extracted from the fat cake by centrifugation. The FA profile of whole milk was analyzed using GC, and the melting properties of milk fat were characterized by differential scanning calorimetry. Data were analyzed by ANOVA with preplanned contrasts testing CON versus PA and CON versus SA at each dose level. Increasing PA progressively increased palmitic acid in milk fat, whereas increasing SA progressively increased both stearic and oleic acid. At 750 g/d, PA increased palmitic and palmitoleic acid in milk fat 5.7 and 0.25 percentage units compared with CON, whereas SA increased stearic and oleic acid in milk fat by 2.4 units and 3.0 units compared with CON. The SFC of milk fat at 20°C was linearly increased by PA but was decreased by SA. At the 750 g/d dose, PA increased SFC by 5.3 percentage units, whereas SA decreased it 3.2 percentage units compared with CON. In conclusion, increasing palmitic acid intake increases the SFC of milk fat at room temperature, whereas increasing stearic acid modestly decreases it, likely due to differences in the rates of desaturation of these FA by the stearoyl-CoA desaturase enzyme.