Embryonic Thermal Manipulation Affects Body Performance Parameters and Cecum Microbiome in Broiler Chickens in Response to Post-Hatch Chronic Heat Stress Challenge

Abstract

Rising global temperatures challenge poultry production by disrupting the cecal microbiota, which is essential for chicken health. Thermal manipulation (TM) during embryogenesis is a potential strategy to enhance thermotolerance in broilers. This study examined TM&rsquo;s effects on the cecal microbiome, body weight (BW), and body temperature (BT) under chronic heat stress (CHS). Fertile Indian River eggs (<i>n</i> = 800) were incubated under control (37.8 &deg;C, 56% RH) or TM conditions (39 &deg;C, 65% RH for 18 h per day from embryonic day 10 to 18). On post-hatch day 18, male chicks were assigned to either CHS (35 &plusmn; 0.5 &deg;C for five days) or thermoneutral conditions (24 &plusmn; 0.5 &deg;C). The CHS-TM group showed a significantly higher BW than the CHS-CON group (<i>p</i> &lt; 0.05). Under thermoneutral conditions, TM chicks had a lower BT on day 1 (<i>p</i> &lt; 0.05), while the CHS-TM group exhibited a non-significant BT reduction compared to the CHS-CON group under heat stress (<i>p</i> &gt; 0.05). An analysis of the gut microbiome showed that the beta diversity analysis (PERMANOVA, <i>p</i> &lt; 0.05) indicated distinct microbial shifts. Firmicutes and Bacteroidota dominated the phylum level, with CHS increased Bacilli and <i>Lactobacillus</i> while reducing Lachnospirales in the CHS-TM group. These findings suggest that TM modulates gut microbiota and mitigates BW loss, offering a potential strategy to enhance broilers&rsquo; resilience to heat stress.