Combined dietary effects of supplemental threonine and purified fiber on growth performance and intestinal health of young chicks.

Characterization of intestinal health in poultry has become imperative as specialized ingredients become more common in poultry diets. We tested whether purified fiber affects dietary Thr requirements and intestinal morphology of young chicks. In experiment 1, three diets containing 7% added silica sand (control), cellulose, or high-methoxy pectin were used. Six replicate pens of 6 chicks received dietary treatments through d 14 posthatch, at which time growth performance and nutrient digestibility were determined. In experiment 2, the effect of purified fiber on dietary Thr requirements was determined using a Thr-deficient basal diet (3.2 g of Thr/kg of diet) and 7 graded levels of supplemental Thr (0 to 9.6 g/kg of diet). Six replicate pens of 5 chicks were tested from d 8 to 21 posthatch, and ileal tissue was collected at the conclusion of the study for histological evaluation. In experiment 1, pectin reduced (P < 0.05) weight gain, feed efficiency, DM digestibility, and AME(n) compared with the control diet. In experiment 2, supplemental Thr requirements were estimated by fitting growth performance data to a 1-slope, broken-line (i.e., piece-wise) regression model. For the control and cellulose- and pectin-containing diets, supplemental Thr requirements were estimated at 3.64, 2.60, and 2.38 g of Thr/kg of diet, and at 778, 737, and 576 mg of supplemental Thr intake over the 21-d study, respectively, based on BW gain. For histological measures, crypts were deepest (P < 0.03) in the cellulose treatment; total goblet cell count and density were highest (P < 0.03) in the pectin-fed birds, and mixed goblet cell counts were highest (P < 0.03) in the control treatment. The serosa was thickest in the cellulose treatment with adequate supplemental Thr, and acidic and neutral goblet cell counts were highest in the control treatment with adequate Thr supplementation (fiber × Thr, P < 0.05). These findings suggest both dietary Thr concentration and fiber source affect growth performance, intestinal morphology, and mucin secretion in young chicks, which may directly affect poultry feeding strategies.