Titration of dietary histidine during a 15 to 35 d feeding period in male Cobb 500 broilers

Dietary CP reductions in broilers can result in increased FCR when 6 or 7 feed-grade amino acids are allowed to enter formulation, and a partial explanation may be a dietary limitation of His. Histidine requirement data are sparce in the current body of literature, especially beyond 3 wk post-hatch. Therefore, a His dose-response experiment (expressed as a percentage of Lys) was conducted with male Cobb 500 broilers from 15 to 35 d post-hatch. A His deficient test diet was formulated to contain a digestible His to digestible Lys (dHis:dLys) ratio of 28.0%. Graded increments of L-His were added to the test diet to produce additional diets containing dHis:dLys ratios of 30.5, 33.0, 35.5, 38.0, 40.5, and 43.0%. A positive control (PC) diet was formulated to contain a dHis:dLys ratio of 38.0% met solely with intact protein. The PC diet outperformed the test diet in all live performance parameters and had a reduced peritoneal cavity fat yield. Linear responses to His were observed for final BW, BW gain, and FCR. In addition, a linear His response was observed for carcass yield and both linear and quadratic responses were observed for breast filet and tender yields. The 95% quadratic max method was used to derive the optimal dHis:dLys ratios of 39 and 37% for breast filet and tender yields, respectively. To accurately estimate quadratic asymptotes for live performance parameters, future His dose-response experiments may need to incorporate dHis:dLys ratios higher than 43%.