Barley does not change threonine requirement in growing pigs fed a barley–casein-based diet compared to a casein-based diet, as determined by the indicator amino acid oxidation method

• Threonine requirement in pigs – barley–casein versus casein.
• Threonine requirement assessed by oral indicator amino acid oxidation technique.
• Additional fiber in casein–barley diet did not increase threonine requirement.
• Two-phase linear and quadratic models gave similar threonine requirement values.

Ileal threonine (Thr) losses increase when young pigs are fed high fiber ingredients such as barley. Barley contains several anti-nutritive factors, e.g., insoluble fibers, which stimulate the secretion of intestinal mucin, a Thr-rich glycoprotein. We hypothesized that because the gut utilizes the majority of dietary Thr, primarily for mucin synthesis, an increase in mucin secretion and ileal losses of Thr will increase the whole body Thr requirement. The objective of this experiment was to compare the Thr requirement of pigs fed a barley–casein diet to a casein diet, using the indicator amino acid oxidation technique. Six barrows were fed diets containing 12% casein or 50% barley/6% casein at 50 g/kg body weight/d. After a 7-d adaptation on the 0.35 g Thr/kg body weight casein-based diet, pigs were fed casein diets with each of seven Thr levels (0.21–0.54 g Thr/kg body weight in a random order) for 2-d with phenylalanine oxidation measured at the end of each period. After a 10-d adaptation to the barley-based diet, the same protocol was followed for barley-based diets with seven Thr levels in the same pigs. Using two-phase linear regression crossover analysis to determine breakpoints in individual pigs, the requirement on casein diet was 0.355±0.014 g Thr/kg body weight/d, and 0.397±0.038 g Thr/kg body weight/d on barley diets. Overall there was no difference (P>0.05) in Thr requirement between diets.