The effect of level of intake and free fatty acid content on the metabolizable energy value and net absorption of tallow by the laying hen

SUMMARY The metabolizable energy (ME) values and net absorption of tallows containing 20, 40, 60, 80 or 98% free fatty acids were determined using mature laying hens. By restricting food intake, the intake of the tallows was controlled to 3, 5, 10 or 20 g per bird d. The tallows were added to a diet of known ME content and the ME's of the tallows were calculated from the data collected from 6- or 7-day energy balances. ME and net absorption values of the tallows were significantly ( P < 0·001) lowered when the level of intake was increased from 3 to 20 g/bird d. The values were also significantly (P < 0·001) lowered when the free fatty acid content was increased from 20 to 98%. The effects of free fatty acid level ( F ) and level of intake ( L ) on the ME and net absorption values were considered in terms of curved surfaces represented by equations embracing the factors and their product. The equations obtained were: ME(kcal/g) = 8·745 – 0·004 F – 0–361 log 10 L –0·011 F log 10 L , Net absorption (%) = 95·82 + 0·02 F – 4·65 log 10 L – 0.13 F log 10 L .