Increasing digesta viscosity altered nutrient transporter gene expression and decreased nutrient utilisation in <i>Eimeria</i> -challenged birds

1. Two experiments were conducted, the first was to investigate the effect of increasing digesta viscosity by dietary carboxymethyl cellulose (CMC) on the growth performance and intestinal morphology and characteristics of healthy birds. The second experiment evaluated the impact of increased digesta viscosity in birds during an <i>Eimeria</i> spp. challenge.2. In experiment 1, a corn-soybean meal-based basal diet was supplemented with 0, 10 or 20 g/kg CMC at the expense of cornstarch and offered to seven birds in each of eight replicate cages per diet from d 8 to 22 post hatching.3. Increasing digesta viscosity due to dietary CMC linearly reduced (<i>p</i> < 0.05) body weight (BW) gain and the apparent ileal digestibility of nutrients. The relative lengths of the duodenum, jejunum and ileum linearly increased (<i>p</i> < 0.01) with dietary CMC inclusion.4. In experiment 2, on d 14, 256 broiler chickens were randomly assigned to eight replicate cages in a 2 × 2 factorial arrangement of treatments with two CMC concentrations (0 or 10 g CMC/kg of diet), with or without an <i>Eimeria</i> challenge. On d 15, birds in the challenge groups were orally gavaged with a 1 ml solution containing 25,000, 25,000 or 125,000 oocysts of <i>E. maxima</i>, <i>E. tenella</i> and <i>E. acervulina</i>; or 1% PBS, respectively.5. Increasing digesta viscosity in <i>Eimeria</i>-challenged birds decreased the total tract digestibility of dry matter and gross energy (<i>p</i> < 0.05). The ileal gene expression of glucose transporters was upregulated (<i>p</i> < 0.05) in challenged birds that received the CMC-supplemented diet.6. In summary, increased digesta viscosity induced changes in the expression of nutrient transporter genes and decreased nutrient utilisation in <i>Eimeria</i>-challenged birds.