Impacts of chronic cyclic heat stress and dietary supplementation of encapsulated clove extract on performance, blood gas status, meat quality, and ileal histomorphometry of broilers

Our objective was to test impacts of heat stress (HS) and dietary supplementation of encapsulated clove extract (ECE) on performance, ileum morphology, and meat quality of broiler chickens. Using a 2 × 2 factorial design, we tested thermoneutral (TN; 23 °C) and chronic cyclic HS (33 °C for 8 h/day) conditions, with or without dietary ECE (4 g/kg; 20% clove extract, 1:4 core-to-wall ratio). During acclimation (days 15–21), HS room temperature was increased from 28 °C to 33 °C for 8 h/day, reaching 33 °C by day 21 and maintained through day 35. All birds received a common starter diet from days 1–14, after which the experimental phase commenced (days 15–35). On day 15, a total of 128 straight-run birds (mean = 565 ± 16.9 g/bird/pen) were redistributed into 16 floor pens (8 birds/pen). Birds kept under HS condition demonstrated a reduction in performance (from days 15–35), as reflected by a reduced average daily gain (ADG; P < 0.01), a trend for reduced feed intake (P = 0.09), and thus poorer feed conversion ratio (FCR; 1.32 vs. 1.40; P = 0.09). Exposure to HS vs. TN resulted in a lower breast muscle weight (18.2% reduction; P < 0.01), increased respiration rate (71 vs. 125 breaths/min; P < 0.01), induced respiratory alkalosis, and reduced circulating potassium concentration. Meat redness (a*) and yellowness (b*) were reduced (P = 0.01 and P = 0.02, respectively) and breast muscle cooking loss increased in HS- vs. TN-exposed birds. Exposure to HS impaired intestinal morphology, as reflected by decreased villus height and crypt depth. Dietary ECE supplementation had no impact on feed intake but increased ADG, resulting in an increased FCR (1.33 vs. 1.40 from days 15–35; P = 0.05). ECE supplementation also tended to increase meat tenderness, as indicated by a reduced Warner-Bratzler shear force (P = 0.07). Illeal histomorphometric indices (villus height and crypt depth) were improved by ECE supplementation. A significant temperature × diet interaction (P = 0.04) was observed for cecal short-chain fatty acid (SCFA) concentrations, as ECE supplementation had no effect on SCFA concentration under TN conditions but helped to maintain total SCFA level in birds in HS group comparable to those kept under TN conditions. The interaction between ECE supplementation and temperature tended to be significant for respiration rate (P = 0.06), as ECE supplementation tended to decrease respiration rate only in birds exposed to HS but not TN conditions. Our data demonstrates that HS compromises performance, meat color, and integrity of ileum tissue in broilers. Dietary ECE supplementation improved FCR, improved meat tenderness, and intestinal tissue integrity in birds kept both under HS and TN and partially contributed to alleviating elevated respiration rate in HS-exposed birds.