HEMICELLULOSE DOES NOT AFFECT IRON BIOAVAILABILITY IN CHICKS

Two iron repletion experiments using hemoglobin as a response criterio n were conducted to assess effects of hemicelluloses on iron bioavaila bility to chicks. In Experiment 1, iron bioavailability from intact fi ber sources was determined by adding tomato pomace (14.6% hemicellulos es), soybean hulls (20.6% hemicelluloses), beet pulp (21.5% hemicellul oses), orchard grass (24.1% hemicelluloses) and corn fiber (55.2% hemi celluloses) to a casein dextrose basal diet providing 0.4-4.1% hemicel luloses to the diet. Test foods were analyzed for iron, total dietary fiber, neutral. detergent residue, neutral detergent fiber, acid deter gent fiber, acid detergent lignin, pectins and uronic acids. Hemicellu loses were determined by the difference of neutral detergent residue m inus acid detergent fiber. Iron bioavailability was determined by the standard curve method to be (percent relative to ferrous sulfate using hemoglobin as the response criterion) as follows: tomato pomace, 82.0 ; soybean hulls, 94.0; beet pulp, 26.5; orchard grass, 68.9; corn fibe r, 69.4. Iron bioavailability was not related to hemicellulose content of test foods or diets. In Experiment 2, the effect of psyllium husk (a fiber source that contains predominantly hemicelluloses) on iron bi oavailability from ferrous sulfate was assessed. Bioavailability was d etermined by the slope ratio method where treatments consisted of grad ed levels of ferrous sulfate in the presence and absence of 5% dietary psyllium. Although iron intrinsic to psyllium was unavailable, bioava ilability of ferrous sulfate iron was not affected (P > 0.05) by the p resence of psyllium. Thus, there was no clear effect of hemicelluloses on iron bioavailability. However, some feeds that contained high leve ls of hemicelluloses had low intrinsic iron bioavailabilities, suggest ing that other dietary factors are primarily responsible for determini ng iron bioavailability from these feed components.