Influence of Dietary Fat on Energy Utilization by Laying Hens

Feed grade fat was included at levels of 2 to 6% in corn-based laying hen rations and at levels of 3 to 6% in laying hen rations containing 8% wheat middlings. Added fat did not affect rate of egg production or average egg weight during the 196-day experiments. Feed consumption and efficiency of feed utilization were improved by added fat. Ration metabolizable energy (ME), as measured experimentally, was increased more than expected on the basis of commonly accepted ME values of feed grade fat when fat levels of 4 and 6% were used in corn-based rations. This effect of fat was most pronounced with the rations containing 8% wheat middlings. Assuming that the entire increase in ration ME's associated with added fat was due to fat per se, estimates of the ME content of fat were 8675 and 9015 mcal/kg when used in corn-based rations. When used in the ration containing 8% wheat middlings, the apparent ME of fat exceeded its gross energy content considerably, indicating an interaction effect between added fat and ingredient composition of the ration. Dietary fat level did not change the proportion of ME consumed that was converted to egg energy. Dietary ME to egg energy conversions ranged from 25.7 to 27.9%. The proportion of ME used for weight gain was increased slightly by added fat while no consistent changes in energy estimated as heat increment were observed.