Effect of adding magnesium salts or different emulsifiers to a fatty acid prill on fatty acid digestibility and milk fat production in lactating dairy cows

Fatty acid (FA) supplements are commonly fed to increase the energy content of lactating dairy cow diets and improve milk and milk fat yield and energy balance. However, increasing dietary fat commonly decreases FA digestibility. Our objective was to investigate the effects of of magnesium salts of fatty acids or exogenous emulsifiers in a FA prill on milk yield and composition and FA digestibility. Fifteen multiparous Holstein cows were randomly assigned to treatment sequence in a 5 × 5 Latin square design with 14-d periods. The treatments were (1) conventional FA prill (CON; 51.2% 16:0, 31.7% 18:0, 7.11% cis-9 18:1) or FA prills that contained (2) magnesium salts of FA (2.2% Mg; MAG), (3) lysophospholipids (LYSO), (4) 18:0 monoglyceride (MONO), or (5) polysorbate 60 (POLY). All cows received the same basal diet and the FA prills were fed at 2% of diet DM. Treatments had no effect on DMI, milk yield, or milk fat and protein concentration or yield. The addition of lysophospholipids increased the concentrations of preformed FA in milk compared with CON, primarily driven by an increase in cis-9 18:1. The addition of polysorbate increased 16 C FA digestibility compared with MAG and MONO. There was no effect of treatment on total or 18 C FA digestibility. Both MONO and POLY decreased NDF digestibility compared with CON and MAG, but there was no effect on DM digestibility. Overall, addition of emulsifiers resulted in changes in 16 C FA digestibility and preformed FA, indicating modification of FA absorption, but these did not translate to changes in milk production. Future work should explore rumen protection and possibly other types of these emulsifiers.