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 caseinbased
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 twophase
linear regression crossover analysis to determine breakpoints in individual pigs, the
requirement on casein diet was 0.35570.014 g Thr/kg body weight/d, and 0.39770.038 g
Thr/kg body weight/d on barley diets. Overall there was no difference (P40.05) in Thr
requirement between diets.