Threonine needs based on Ross manuals might be 14% of the National Research Council (NRC) recommendation, thus the effect of threonine on mucin2 gene expression, histological characteristics and performance were evaluated in Ross male broilers fed diets containing 0.8% (NRC requirement), 0.87% (average of NRC and Ross requirement), 0.94% (Ross requirement) and 1.01% (more than Ross requirement) total threonine. The dietary treatments consisted of an isonitrogenous corn-soybean meal-based diet with incremental levels of threonine. At the first day of chicken age, 24 pens were equalized to 12 birds per pen, in a completely randomized design and dietary treatments were randomly distributed for the 14-d period. Live performance measurements improved (P<0.05) as dietary threonine increased from 0.8% to 0.87%. The least performance was related to diet containing 1.01% threonine. Histological assays showed that villi height, crypt depth and villi surface increased as dietary threonine increased from 0.8% to 0.87% and decreased in 0.94% and 1.01% threonine. There was no effect of threonine on mucin2 gene expression and goblet cells density. According to these results, threonine needs in starter period in Ross (308) broilers is more than NRC recommendation.

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