Chronic Heat Stress Effect on Metabolic Parameters of Poultry: A Meta-Analysis

Many scientific researchers reported the significant effect of heat stress (HS) on commercial poultry production. Bird metabolism and blood parameters change during acute and chronic heat stress status. This article reviewed and analyzed the broiler blood parameters under normal thermal and cyclic-chronic heat stress conditions. All the reviewed reports were achieved from Elsevier, PubMed, Web of Science, and Google Scholar those were in English up to January 27, 2022. Outcomes of blood cholesterol (Chol), triglyceride (Tri), glucose (Glu), corticosterone (Cortico), uric acid (UA), sodium (Na+), Potassium (K+), and triiodothyronine (T3) were calculated by standardized mean difference (SMD) with 95% confidence interval (CI). Articles with common metabolite differentiated between 4 or 7 studies with 94-662 chicks in each of them. Chronic HS had no significant effect on blood concentrations of Cortico (5 studies: SMD=1.8153 95% CI=-2.9524; 6.5830), Tri ( studies=7 SMD=0.4559 95% CI=-0.2923; 1.2040), Uric (studies=5 SMD= 0.9590 95% CI= -0.3338; 2.2518), T3 (studies=4 SMD= -9.006 95% CI= -46.1608; 28.1487), K+ (studies=4 SMD= -6.675 95% CI= -20.1400; 6.7898) , but significantly increased Glu (studies=8 SMD= 0.3064 95% CI= 0.0027; 0.6100), Chol (studies=6 SMD= 0.7655 95% CI= 0.2653; 1.2658) and decreased Na+ (studies=4 SMD= -1.723 95% CI= -3.1536; -0.2925) levels. Statistically significant effects of chronic heat stress reflexed as a decrease in serum sodium, increase in cholesterol, and glucose level. But there was no significant difference between triglyceride, corticosterone, uric acid, potassium, and triiodothyronine in the heat stress and normal temperature group. Based on our meta-analysis, high blood glucose, high Cholesterol, and losing electrolyte balance are major problems in chickens during cyclic-chronic heat stress acclimatizing programs.