Beside from commercial broilers, chickens are the extremely rich source of genetic diversity and could have different reaction to microbiome stimulation by in ovo delivery of prebiotics. The aim of the study was to evaluate carcase and meat quality traits in slow-growing chickens stimulated in ovo with trans-galactooligosaccharides (GOS) and exposed to heat stress. Fertilised eggs from Hubbard JA57 chickens were incubated. On the day 12 of egg incubation, 3000 eggs were divided into: prebiotic group (GOS) injected with a single dose of 3.5 mg GOS/egg, saline group (S) injected with physiological saline and control group (C) un-injected. After hatching, 900 male chicks were reared in floor pens: three groups (GOS, S and C, 6 pens/group, 25 birds/pen) reared in thermoneutral conditions (TN) and three groups (GOS, S and C, 6 pens/group, 25 birds/pen) reared under heat stress conditions (HS). Chronic heat stress (30 °C) was applied from day 36 to 50. At 50 days of age, 15 randomly chosen birds/treatment/ temperature were slaughtered and pectoral muscle (PM) was removed for the analyses. Data were analysed by GLM procedure in a 3 × 2 factorial design: treatment and temperature were the main factors. Treatment had no influence on carcase weight. GOS reduced (p<.05) PM weight and its yield as compared to C group. As expected, temperature had a strong effect on carcase and PM weight, significantly lower in HS group. Muscle pH was higher (p<.05) in GOS group compared to C. Meat from GOS group showed a lower lightness and a higher redness compared to C and S groups. WHC, proximate composition, cholesterol and intramuscular collagen were not affected by treatment. Heat stress increased moisture (p<.01) and reduced protein (p<.05) content. Cholesterol and collagen contents were not affected by temperature. Neither fatty acid composition (total saturated, monounsaturated and polyunsaturated fatty acids) nor nutritional indices of meat were significantly affected by treatment and temperature. Significant interactions between factors were observed for carcase weight, protein and lipids contents, and for n6/n3 ratio. In conclusion, in ovo injection of the GOS prebiotic had no negative effect on physico-chemical and nutritional properties of meat produced by slow-growing broiler chickens reared under intensive conditions, but reduced weight and yield of breast muscle. Heat stress has a negative and marked effect on carcase traits and reduced the protein content.
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