Evaluating the effect of palmitic acid supplementation on molar shifts in milk de novo and preformed fatty acids: A meta-analysis and meta-regression

To determine the effect of supplemental palmitic acid (PA) on the molar and mass yields of milk fatty acid (FA) sources and individual FA, a meta-analysis and meta-regression were conducted using 1,240 individual cow observations from 13 studies conducted at Michigan State University. All studies included a control diet (CON) with no supplemental PA (n = 581) and a diet supplemented with a PA-enriched prill or a blend of FA supplements containing ≥75% and ≤95% PA (n = 659) fed at (mean ± SD) 1.54% ± 0.13% of diet DM. The statistical model for the meta-analysis and meta-regression included the random effects of study, cow within study, and period or day of treatment within study. A meta-regression was used to determine the effect of increasing dietary PA intake on the yields of milk FA sources. Sources of FA were classified as de novo (<16 carbons), mixed (16-carbon), and preformed (>16 carbons). Molar yields of individual FA were calculated using the FA mass yield (g/d) and the individual FA molecular weight. Supplementation of PA had no effect on de novo FA molar yield but increased C4:0 yield and decreased the yields of medium-chain FA. Compared with CON, PA increased mixed FA yield by increasing the yields of C16:0 and cis-9 C16:1. Supplementation of PA had no effect on preformed FA yield, but it decreased C18:0 yield and tended to increase cis-9 C18:1 yield. In the meta-regression, increasing dietary PA intake had no effect on de novo FA yield, linearly increased mixed FA molar yield, and had no effect on preformed FA molar yield. In summary, supplementation of PA increased mixed FA molar yield while shifting de novo and preformed FA in favor of increased C4:0 and unsaturated FA likely to balance the increased incorporation of saturated FA. Future research should evaluate the effects of altering the supply of de novo and preformed FA on the molar yields of milk FA to ascertain their influence on the incorporation and regulation of FA into milk fat.