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Literature data indicate that feed intake is sensitive to the dietary Lys content particularly in fast-growing birds. From a conceptual and a practical viewpoint, an interaction between genotype (i.e., fast-growing vs. slow-growing birds) and dietary Lys content is of interest, but it needs confirmation owing to a dearth of studies addressing this issue. A study was conducted with 266 Cobb 500 birds and 266 Thai native crossbreed birds serving as models for fast-growing broilers ( FGB ) and slow-growing broilers ( SGB ), respectively. Within genotype, chicks were randomly allocated to diets containing either a high ( H-LYS = 1.36%), medium (1.17%), or low Lys (1.01%) content. Growth performance and the accretion of protein and selected amino acids were determined in birds from 1 to 21 d of age. Treatments were arranged in a factorial design with 6 replications/treatment. Low Lys vs. H-LYS caused a 42.1% lower feed intake in FGB ( P < 0.001), but not in SGB ( P = 0.596). The feed conversion ratio ( FCR (g feed/g BW gain)) was lowest in FGB ( P < 0.001) and increased with decreasing dietary Lys contents ( P < 0.001). The Lys induced increase in FCR, however, was more pronounced in SGB ( P = 0.025). The absolute protein gain (g/bird) was influenced by the Lys content of feed and decreased by ∼54% and ∼23% in FGB and SGB, respectively ( P < 0.001). The efficiency (% of intake) of protein accretion was found to be greater in FGB ( P ≤ 0.001) and decreased with decreasing dietary Lys ( P ≤ 0.001). The efficiency of Lys accretion was found to be negatively affected by the dietary Lys content in FGB ( P < 0.001) but not SGB ( P genotype × dietary Lys = 0.008). It can be concluded that a dietary Lys content of 1.01% does not safeguard both growth performance and body protein accretion efficiency in both FGB and SGB. The suboptimal growth performance in FGB, but not SGB, is partially counteracted by a Lys-induced reduction in feed intake.

The objective of this study was to investigate the influence of particle size, texture, and gastric viscosity on food gastric disintegration and emptying rates. In vitro dynamic gastric digestion was conducted for carrots using a dynamic gastric simulation model. The changes in the texture of carrots and other foods as indicated by bulk resistance, the percent solids emptied, and the particle size distribution were used as parameters to study disintegration kinetics and emptying patterns. The influence of viscosity on food emptying was studied on both indigestible particles (amberlite beads) and digestible solids (carrots). The results indicated medium-size carrot particles (1.40-2.00 mm) had a greater disintegration and a higher amount of emptying rate when compared to larger (2.00-3.34 mm) and smaller (1.14-1.40 mm) carrot particles. A high correlation exists between the final bulk resistance after 120 min digestion and the amount of solids emptied. Increasing viscosity up to values 8.20 Pa•s improved the particle dispersion for amberlite and carrots and increased rates of solids emptying, while further increase in viscosity hindered emptying of amberlite and carrot solids. The variable emptying rates of both indigestible and digestible solids with viscosity were described with a mathematical model based on particle-emptying coefficient.

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