Evaluating the Dietary Effects of White Grape Pomace Supplementation in Laying Hens Exposed to Thermal Stress: Hematological, Biochemical, Cecal Fermentation Metabolites, Histomorphology Approaches

This study aimed to investigate the hematological, biochemical, short-chain fatty acids (SCFAs) content, and histomorphological responses of laying hens exposed to different thermal stress conditions and fed a diet supplemented with 6% white grape pomace (WGP). The research was part of a large six-week experimental trial conducted on 240 Lohmann Brown hens (58 weeks old), arranged in a 2 × 3 factorial design with two dietary treatments (control and WGP) conducted under thermoneutral (NT, 22 °C), high thermal stress (HST, 35 °C), and low thermal stress (LST, 10 °C) conditions. HST conditions significantly lowered the production performances of ALBW (average live body weight; p = 0.0001) and ACW (average carcass weight; p = 0.026) and significantly increased the heterophil/lymphocyte (H:L) ratio and platelets concentration (p < 0.05). Serum K values decreased and the Na/K ratio increased significantly (p = 0.001) under both HST and LST conditions; total protein (TP) decreased significantly under HST (p = 0.031). Significantly decreased (p < 0.001) feed intake and excreta were registered under HST conditions. Concerning SCFAs content, isobutyrate was higher under LST (p = 0.0001), while butyrate showed higher values under NT conditions for the WGP group (p = 0.002). Intestinal morphometry was highly influenced by high temperatures (shorter villi, deeper crypts). Overall, the 6% WGP supplementation, a natural high antioxidant resource, produced modest, context-dependent effects, with benefits under NT and LST conditions but insufficient to protect against the negative effects of chronic heat stress.