Synbiotic containing fructooligosaccharides and multi-species probiotic strains and its effects on growth, intestinal morphology, tibia strength, and caecal microbiota in Cobb 500 and Ross 308 broilers

The study assessed the effect of a synbiotic-supplemented diet on the performance, gut health, skeletal health, and fear response of two commercial broiler strains. Three-hundred-day-old Cobb 500 and Ross 308 chicks were randomly allotted to either only a basal diet or a diet supplemented with antibiotic or synbiotic (consisting of fructooligosaccharide, Enterococcus sp., Bifidobacterium sp., Pediococcus sp., and Lactobacillus spp. at 0.5 g/kg of diet). The birds' body weight (BW) and feed intake were measured weekly, and the tonic immobility and latency tests were conducted on days 32 and 35 of age, respectively. The birds were slaughtered on day 35, and the analysis included quantification of duodenum morphometrics and caecal bacteria and evaluation of leg and tibia strength. Diets had a negligible effect (p > 0.05) on bird BW, feed intake, relative internal organs (liver, gizzards, and heart weight), caecal bacterial population, and fear response. The synbiotic did not improve the birds' leg strength, although they had higher tibia weight (p = 0.02) and dry matter (p = 0.008) than antibiotic-supplemented birds. Additionally, synbiotic-supplemented birds had higher villus height and shorter villus width of duodenum compared to the other groups (p < 0.01), and broilers fed only the basal diet (p < 0.05), respectively. The Cobb 500 birds consumed more feed (p = 0.0001) and were heavier (p < 0.0001) than the Ross 308 birds, but no strain differences (p > 0.05) were observed for the tibia strength and caecal bacterial counts. The findings of this study indicate that Cobb 500 birds had a better performance than Ross 308. Although the synbiotic increased the duodenal villi's height and tibia's weight, it did not affect both bird strains' growth performance and leg strength. Therefore, the optimum amount of synbiotic required to enhance the overall performance of broiler chickens warrants further study.