Effects of physical form of diet and intensity and duration of feed restriction on the growth performance, blood variables,microbial flora, immunity, and carcass and organ characteristics of broiler chickens
This study was conducted to investigate the effects of physical form of diet and duration and intensity of feed restriction on growth performance, carcass and organ characteristics, immunity, cecal microbiota, and hematology of broiler chickens. Four hundred male broiler chickens (approximately 44.0. g) were randomly assigned to 10 treatment groups with 4 replicate cages with 10 broiler chickens per cage. Dietary treatments consisted of diet form (pellet and mash), intensity of feed restriction (12.5 and 25%), and duration of feed restriction (7 and 14. d) in a 2×2×2 factorial arrangement of treatments. Two additional treatments, pellet and mash control diets without feed restrictions, were included. Feed intake (FI) and weight gain (WG) were recorded weekly. At the end of the study (at 42. d of age), 1 chicken per replication and 4 chickens per treatment were selected for blood collection. Carcass composition, cecum microflora, and characteristics of gastrointestinal tracts were also assessed. The humoral immune responses of chickens to Newcastle vaccine, influenza vaccine, and sheep red blood cells (SRBC) were measured at 15 and 26, 31 and 40, and 28 and 35 d of age, respectively. Broiler chickens fed the pelleted diet had greater FI (. P<0.01), WG (. P<0.01), carcass weight (. P<0.01), and breast (. P<0.01) relative to the carcass weight, better feed conversion ratio (. P<0.01), and lower weight of pancreas (. P<0.01), duodenum (. P=0.02), and cecum (. P<0.01) relative to the carcass weight than those fed the mash diet. Compared with broiler chickens fed the mash diet, the Lactobacillus concentration in cecum decreased (. P<0.01) and plasma total protein and globulin concentrations increased (. P=0.01 and 0.02, respectively) in those fed the pelleted diet. Physical form of the diet did not affect antibody titres against Influenza, Newcastle disease, and SRBC. Within the diet form, feed restriction had a limited influence on the traits studied at slaughter compared with the pellet or mash diet feed restriction. In conclusion, the diet form played an important role on the growth performance and carcass characteristics of broiler chickens, whereas the feed restriction seemed to be insufficient to markedly improve the feed conversion ratio and carcass characteristics of broiler chickens at slaughter.