Assessing the effect of rate and extent of starch digestion in broiler and laying hen feeding behaviour

Feeding behaviour can be affected by diet composition as a result of diet density, the rate and extent of ingredient digestion and the activation of nutrient sensing mechanisms. It was hypothezised that the presence of starch in the distal small intestine would activate the ileal brake, thereby increasing satiety, and changing feeding behaviour. Two semi-purified starch sources with differing in-vitro digestibility, wheat (WS, rapidly digested), and pea (PS, slowly digested), were used in four diets containing equal amounts of starch, but differing in WS/PS ratios (100/0, 80/20, 60/40, 0/100). Diets were fed to Ross 308 male (944) and female (1056) broilers housed in 32 litter floor pens from 0 to 28 d. Similar diets were fed to 192 laying hens from 26 to 46 weeks of age, housed in 16 experimental units, comprised of two conventional cages each. Video recordings (24 h) were taken at 27–28 d from four individually marked broilers per pen, and at 46 weeks of age from two hens per experimental unit. Focal observations were used to record the initiation and end of every feeding (broilers, hens) and drinking bout (broilers) over 24 h to calculate number of bouts, bout length, time between bouts, total time during the photo and scotoperiod, and time until first night bout. Data were analyzed as a four (diet) by two (gender) factorial arrangement (broiler) or one-way ANOVA (laying hen) using the SAS 9.4 GLIMMIX procedure. No interactions were found. Diet affected broiler number of visits to the feeder (P = 0.034), as well as time between feeding bouts (P = 0.031) and total feeding time (P = 0.028), but changes appeared random and did not support a satiety hypothesis. Males had more visits to the feeder (P < 0.001) and more total feeding time (P < 0.001) than females, but shorter feeding bout length (P < 0.001), suggesting increased hunger. Drinking behaviour was not affected, except for a longer time between bouts for females (P = 0.046). No effect of diet on day-time hen feeding behaviour was found, but the number of feeding bouts during the scotoperiod increased (P = 0.029) and time to the first night feeding event decreased (P < 0.001) as PS increased, suggesting increased hunger with PS level. In summary, no effect of dietary PS on broiler feeding behaviour was found. However, dietary effects on hen night feeding behaviour suggest that PS increased hunger, in contrast to the hypothesis.