Effect of β-glucan Dietary Supplementation on Performance, Nutrient Digestibility, Immune Response and Heat Shock Proteins in Broiler Chickens under Heat-Stress by Early Heat Acclimation

The study examined the impact of early heat acclimation, heat stress, and β-glucan supplementation on broiler chickens’ productivity, immune parameters, thyroid hormones, gut microbiota, and nutrient digestibility. A total number of 1080 male broiler chicks (Cobb 500) were randomly assigned to nine treatments (3 × 3 factorial arrangement), including heat exposure (control, heat stress, heat shock at 3 days) and three β-glucan levels (0, 100, and 200 mg β-glucan /kg diet). Compared to the thermo-neutral control group, the results showed that in broilers exposed to heat stress or early heat shock, body weight gain and feed intake decreased significantly (p<0.05). Conversely, the mortality rate, antibody titers against the infectious bronchitis (IBV) and Newcastle disease viruses (NDV), immunoglobulin M, immunoglobulin G, liver heat shock protein 70 (HSP70), H/L ratio, and toe web swelling were significantly (p<0.05) increased. Supplementing with βG increased lactobacillus counts while decreasing those of E. coli and total aerobic bacteria. Significant reductions in nutrient digestibility were observed in heat stress or early heat shock exposure, specifically for nitrogen, ether extract, and organic matter.