Abstract #W121

# W121
The yields of individual de novo and preformed milk fatty acids are differentially regulated in response to changes in the intake of palmitic acid in dairy cows.
J. de Souza*1,2, A. L. Lock1, 1Michigan State University, East Lansing, MI, 2Perdue AgriBusiness, Salisbury, MD.

We determined how the intake of palmitic acid (C16:0) alters the yield of individual milk fatty acids (FA) in dairy cows. Our analysis used individual observations (n = 1202) from 212 Holstein cows from 14 studies. Diets (% DM) contained (mean ± SD) 30.6 ± 3.66 NDF, 27.1 ± 2.16 starch, and 4.0 ± 0.97 total FA. Intake of C16:0 averaged 371 g/d and ranged from 60 to 923 g/d. Milk FA were determined by gas-liquid chromatography. Mixed model regressions were developed taking into account study, period within study, and cow within study as random factors. All equations report the relationship between C16:0 intake (g/d) and yield of milk FA (g/d). Overall, no relationship was observed between the intake of C16:0 and the yield of de novo milk FA (<16-carbon FA; P = 0.60) or the yield of preformed milk FA (>16-carbon FA; P = 0.54); however, increasing 16:0 intake linearly increased the yield of 16-carbon milk FA [468 ± 3.23 + 0.23 ± 0.008 × 16:0 intake, P < 0.001, R2 = 0.43]. Among individual de novo synthesized milk FA, increasing C16:0 intake linearly increased the yield of milk C4:0 [43.6 ± 0.12 + 0.092 ± 0.0003 × 16:0 intake, P < 0.001, R2 = 0.45] and C6:0 [26.8 ± 0.07 + 0.008 ± 0.00003 × 16:0 intake, P < 0.001, R2 = 0.32]. No relationship was observed between the intake of C16:0 and yield of milk C8:0 (P = 0.95) or C10:0 (P = 0.32). Increasing C16:0 intake linearly decreased the yield of milk C12:0 [52.1 ± 0.16 − 0.008 ± 0.0004 × 16:0 intake, P < 0.001, R2 = 0.24], and C14:0 [166 ± 0.40 - 0.008 ± 0.00009 × 16:0 intake, P < 0.001, R2 = 0.25]. Among individual preformed milk FA, increasing C16:0 intake linearly increased the yield of milk cis-9 C18:1 [272 ± 1.38 + 0.04 ± 0.003 × 16:0 intake, P < 0.001, R2 = 0.18] and tended to decrease the yield of milk C18:0 [145 ± 10.8 - 0.009 ± 0.0005 × 16:0 intake, P = 0.06, R2 = 0.10]. Our results demonstrate that increasing dietary intake of C16:0 improves milk fat yield due to an increase in the yield of 16-carbon milk FA. Although C16:0 intake does not affect the yield of total de novo FA or preformed FA, specific changes in the yield of some individual de novo and preformed milk FA occurs, which is likely associated with mammary gland plasticity to maintain milk fluidity.

Key Words: fatty acids, meta-analysis, milk fat