Threonine requirement of broiler chickens during subclinical intestinal Clostridium infection

The aim of this study was to determine the threonine requirement of broilers during a subclinical Clostridium infection. Three experiments were performed: experiments 1 and 2 to investigate the dose-response of threonine supplementation during infection and experiment 3 to validate the threonine requirement during infection. In each experiment, 1-d-old Ross 308 male broilers were used. An infection model was used with inoculation of Eimeria maxima and Clostridium perfringens at d 9 and 14 of age, respectively. Control birds were inoculated with saline and liver broth at d 9 and 14 of age, respectively. From d 9 of age, infected birds were fed diets differing in the standardized digestible threonine-to-lysine ratio (realized ratios experiment 1: 0.55, 0.58, 0.63, 0.69, and 0.72; realized ratios experiment 2: 0.64, 0.65, 0.67, 0.69, and 0.72; and realized ratios experiment 3: 0.63 and 0.67). Uninfected birds were fed diets with a realized Thr:Lys ratio of 0.63 in experiments 1 and 2 and of 0.63 or 0.67 in experiment 3. The incidence of lesions, lesion severity, and mortality rate of infected birds was not affected by the Thr:Lys ratio. Experiments 1 and 2 showed that the decrease in BW gain and feed intake was less severe in infected birds fed a diet with a Thr:Lys ratio of 0.69 and 0.67, respectively (not significant). Validation of the Thr:Lys ratio in experiment 3 showed that the BW gain and feed intake were higher for infected birds with a Thr:Lys ratio of 0.67 compared with infected birds with a Thr:Lys ratio of 0.63. This resulted in an increased BW gain and feed intake of 129 and 148 g, respectively, with a higher Thr:Lys ratio over a production period of 37 d. This indicates that a higher Thr:Lys ratio in infected birds improved production performance during infection with C. perfringens, although intestinal damage (incidence and lesion severity) was not affected.