For this study, threonine (Thr) deficiency was hypothesised to exacerbate the intestinal damage induced by feed withdrawal with coccidial infection because of its high obligatory requirement by the gut; two dietary Thr treatments (0·49 and 0·90 %) were applied to chicks from 0 to 21 d of age. At 13 d of age, feed was withdrawn for 24 h from one-half of birds of each dietary treatment with subsequent gavage of a 25× dose of coccidial vaccine. Overall, there were four treatments with eight replicate cages per treatment. Under combined challenge, birds fed the Thr-deficient diet had 38 % lower 13-21-d body weight gain (P≤0·05) compared with birds fed the Thr-control diet. At 21 d, the challenged group fed low Thr had higher number of oocysts (+40 %, P=0·03) and lower crypt depth (-31 %, P0·05). Overall, Thr deficiency worsened the detrimental effects of combined feed withdrawal and coccidial infection on growth performance and oocyst shedding by impairing intestinal morphology, barrier function, lymphocyte profiles and their cytokine expressions.
Keywords: ASCT1 system ASC; BW body weight; CCR9 C-C chemokine receptor type 9; CD crypt depth; CT caecal tonsil; CXCR5 C-X-C chemokine receptor type 5; EAAT3 Na+; FI feed intake; FITC-d fluorescein isothiocyanate-dextran; GC goblet cell; H+; IFN-γ interferon-γ; IL interleukin; K+-dependent excitatory amino acid transporter 3; Na+-dependent neutral amino acid transporter 1; TGF-β4 transforming growth factor-β4; Thr threonine; VH villus height; bo; pIgR/SC polymeric Ig receptor/secretory component; y+LAT1 Na+-independent cationic and Na+-dependent neutral amino acid transporter; ΔBWG change in body weight gain; ΔFI change in feed intake; +AT Na+-independent cationic and zwitterionic amino acid transporter; Chicks; Coccidiosis; Intestinal barrier function; Lymphocyte profiles; Threonine deficiency.