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Two studies were conducted simultaneously and evaluated the Thr needs of male Ross × Ross 708 broilers. Broilers in the 2 studies were reared under 2 litter conditions: new (NL) vs. used built-up soft wood shavings (BL). Separated by a center aisle, all floor pens from 1 side of the close-sided house contained NL, whereas the opposite side contained BL. Broilers received common diets up to 21 d and then were fed 1 of 6 total dietary Thr levels that ranged from 0.51 to 0.86% total Thr until d 42. At 42 d, birds were processed. A subsample of birds from each experimental unit corresponding to either the 0.51 or 0.72% Thr treatments was taken, immune function was quantified, and lymphoid organs were weighed. Results for live performance and carcass traits are in close agreement with previously reported values in the literature. Quadratic responses were observed for BW gain, feed conversion, and carcass and breast meat absolute and relative weights. Depending on the variable, these responses were maximized from 0.71 to 0.74% Thr when broilers were raised on NL and from 0.73 to 0.78% Thr when broilers were raised on BL. Low Thr (0.51%) was without effect on most immune parameters. However, low Thr decreased relative thymus weight and increased monocyte NO production in built-up and new litter environments, respectively.

Sex-separate male and female broilers (2,592 broilers; Ross x 708) were placed in 144 floor pens (12 replications per treatment) and fed diets containing high (H) and moderate (M) amino acid density from 1 to 55 d of age. Diets were formulated using ileal digestible amino acid ratios to Lys. Six dietary treatment combinations (MMMMM, HMMMM, HHMMM, HHHMM, HHHHM, and HHHHH) were implemented in 5 diet phases (1 to 5, 6 to 14, 15 to 35, 36 to 45, and 46 to 55 d of age). Male birds were heavier (P < or = 0.05) and had lower (P < or = 0.05) feed conversion, abdominal fat, and breast yield than female birds. Birds fed H diets in the first 3 phases had optimal (P < or = 0.05) BW and feed conversion (d 35, and 45), but optimal (P < or = 0.05) feed conversion at d 55 warranted H diets in all phases. Breast meat (d 35) and carcass (d 55) relative to BW were highest (P < or = 0.05) in birds fed H diets in the first 3 phases; however, differences in 55 d breast meat yield did not occur. Results indicate that amino acid needs of Ross x 708 broilers are most critical from 1 to 35 d of age. Predicted economic margins were advantageous in birds fed H diets resulting in dollar 0.12 and dollar 0.05/bird more income over feed costs at 35 and 55 d, respectively, in comparison with birds fed M diets.

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