Adaptive response to exercise of fast-growing and slow-growing chicken strains: Blood oxidative status and non-enzymatic antioxidant defense

The adaptation of chickens to free-range rearing systems mainly involves the locomotory behavior, which is very different in fast-growing (FG) and slow-growing (SG) strains. This study aimed to compare the effect of moderate locomotory activity (induced and prolonged) on the blood oxidative status in a slow-growing chicken strain with that in a fastgrowing one. Thirty FG (Ross 308) birds and 30 SG (Hubbard) birds were divided into 2 groups for each strain and subjected to different treatments: no exercise (the control group [C]) and 1 h of walking at 4 km/h (the exercise group [E]). Daily exercise was promoted by operators, who walked behind the animals around a paddock. Blood samples were obtained weeklyfrombothgroups.FortheEgroup,sampleswere obtained before exercise (E1) and after exercise (E2). Oxidative markers (creatine kinase [CK], reactive oxygen molecular substance [ROMS], thiobarbituric acid reactive substances [TBARS]), and antioxidant compounds (α-tocopherol [α-T], γ-tocopherol [γ-T], δtocopherol [δ-T], α-tocotrienol [α-T3], γ-tocotrienol [γT3], retinol, and carotenoids) were evaluated. In both strains, the CK level was higher in chickens subjected to exercise; however, its increase was greater in the FG group than in the SG one (1.56-fold vs. 1.08fold). The antioxidant status was worse in FG strain birdssubjectedtoexercise,whereasthestatusremained nearly the same in the SG strain birds. The α-T and retinol concentrations were significantly reduced by exercise, primarily in the FG group, whereas the other antioxidant compounds (α-T3, γ-T3, γ-T, δ-T, lutein, and zeaxanthin) were unaffected by strain or treatment. The FG and SG strains had different responses to exercise, and only the SG showed a progressive reduction in TBARS and ROMS values during the 28-dayexperiment.Accordingly,moderateexercisemay be beneficial only when the birds have suitable behavioral characteristics (e.g., higher kinetic activity, rusticity, and explorative nature) or physical characteristics (e.g., low body weight); otherwise, exercise is highly stressful and affects physiology and wellbeing.