Effects of timing of palmitic acid supplementation during early lactation on nutrient digestibility, energy balance, and metabolism of dairy cows.

The objective of our study was to evaluate the effects of timing of palmitic acid (C16:0) supplementation during early lactation on nutrient digestibility, energy intake and balance, and metabolic responses of dairy cows. Fifty-two multiparous cows were used in a randomized complete block design experiment. During the fresh (FR) period (1-24 d in milk) cows were assigned to either a control diet containing no supplemental fat (CON) or a C16:0-supplemented diet [PA; 1.5% of diet dry matter (DM)]. During the peak (PK) period (25-67 d in milk) cows were assigned to either a CON diet or a PA diet (1.5% of diet DM) in a 2 × 2 factorial arrangement of treatments considering the diet that they received during the FR period. During the FR period, compared with CON, PA increased DM digestibility by 3.0 percentage units and neutral detergent fiber (NDF) digestibility by 4.4 percentage units, and the increase in these variables was consistent over time. Although PA did not affect 18-carbon fatty acid (FA) digestibility, it decreased 16-carbon FA digestibility by 10.8 percentage units and total FA digestibility by 4.7 percentage units compared with CON. We observed a tendency for an interaction between treatment and time for total FA digestibility and 16-carbon FA digestibility due to the difference in FA digestibility between PA and CON reducing over time. Compared with CON, PA increased digestible energy intake by 3.9 Mcal/d, metabolizable energy intake by 3.5 Mcal/d, and net energy for lactation intake by 2.5 Mcal/d. The PA diet also increased milk energy output, negative energy balance, and plasma nonesterified fatty acid concentration and reduced plasma insulin concentration. We also observed a tendency for an interaction between treatment and time for energy balance due to cows receiving the PA treatment being in a greater negative energy balance over time. During the PK period, PA increased DM digestibility by 2.9 percentage units and NDF digestibility by 3.5 percentage units compared with CON. Although PA decreased 16-carbon FA digestibility by 7.0 percentage units, PA did not affect 18-carbon FA digestibility or total FA digestibility. Feeding PA during the PK period increased energy intake and milk energy output and did not affect energy balance. In conclusion, feeding a C16:0 supplement to early-lactation cows consistently increased DM and NDF digestibilities and energy intake compared with a control diet containing no supplemental fat. Feeding C16:0 markedly increased milk energy output in both the FR and PK periods but increased negative energy balance only in the FR period.

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