abstract
This study was conducted to investigate the effects of graded levels of standard- ized ideal digestible threonine (SIDT) on the small intestinal morphology and immune responses of Escherichia coli K88+ challenged weaned piglets. Thirty-six crossbred (Large White × Landrace) barrows, with an initial BW of 7.34 ± 0.55 kg and weaned at 21 d, were assigned to 1 of 6 treatments according to a 3 (3.7, 7.5 or 11.1 g/kg dietary SIDT content) × 2 (non-challenged or challenged) factorial arrangement. On d 16, half of the piglets in each SIDT treatment were orally challenged with 10 mL E. coli K88+ culture (1 × 109 CFU/mL), while the other half were orally inoculated with the same amount of phosphate buffer (PBS). On d 18 (on 2 d after E. coli challenged), the pigs were killed and blood and intesti- nal samples were collected. The average daily gain (ADG) and feed conversion ratio (FCR) of piglets receiving the 7.5 and 11.1 g/kg SIDT diets were significantly improved (P