Effect of rate and extent of starch digestion on broiler chicken performance.

Dietary starch with lower rate and extent of digestion improves broiler feed efficiency, but previous results might have been confounded by non-starch components of the grains. Therefore, the objective of this research was to study the effects of starch digestion on broilers using semi-purified starch. Semi-purified wheat (WS, rapidly digested) and pea (PS, slowly digested) starch were combined to create 6 WS:PS ratios (100:0, 80:20, 60:40, 40:60, 20:80, and 0:100) in starter, grower and finisher diets. Each treatment was fed to Ross 308 male (2,124) and female (2,376) broilers housed in 72 L floor pens from 0 to 31 d of age to measure performance and meat yield relative to live weight. On day 33, the effects of diet on 8 h feed withdrawal was assessed in 20 males per treatment. Data were analyzed with ANOVA and linear and quadratic regression analyses using SAS 9.4. Significance was accepted at P ≤ 0.050. Body weight gain declined linearly with increasing PS. Male feed intake decreased with increasing PS, but PS did not affect female feed intake. Mortality corrected gain:feed ratio was quadratically influenced by diet (estimated maximum at 25% PS). Breast meat increased linearly with PS, while fat pad and breast and thigh skin decreased linearly. Quadratic responses were found for thigh meat and whole drum (estimated maximum values at 56 and 54% PS, respectively). Males grew faster, ate more, and had higher mortality than females. They also had heavier pectoralis major, thigh bone, and whole drum, while females had heavier pectoralis minor and more breast and thigh skin. After feed withdrawal, digesta content decreased linearly with time in all sections, except for the crop and duodenum, which declined quadratically. Ileal digesta pH increased linearly with time, while crop and caecal pH decreased for 2 h before steadily increasing. Diet did not affect digestive tract emptying or digesta pH. In conclusion, dietary PS maximized feed efficiency at 25% PS and linearly improved breast meat yield, but did not affect digesta clearance after feed withdrawal.