Influence of environmental enrichment on circulating white blood cell counts and behavior of female turkeys
Under commercial conditions turkeys are housed in large groups in poorly structured environments. This leads to stress and subsequently to pecking and cannibalism. Environmental enrichment is suggested to reduce stress and feather pecking, thus leading to an increase of the overall flock health. However, the effect of increasing age on the use of enrichment elements and on the behavior repertoire as well as its correlation with health parameters has scarcely been studied. Therefore, our objective was to investigate the influence of environmental enrichment on the behavioral repertoire and on health parameters of turkeys. In three consecutive trials, female turkeys were housed up to 12 weeks either in an unstructured (control group) or enriched environment (EE group) featuring elevated plateaus at different levels (“turkey tree”). Behavior parameters, clinical health, and immune parameters were determined at selected time points. The percentage of birds using the turkey tree increased with age up to 55-77% at 22-30 days post hatch (dph). Thereafter, the number of birds located on the turkey tree decreased to 25-32% at 73 – 79 dph. Feather pecking and fighting was significantly lower in the EE group compared to the control group in two and three trials, respectively (p < 0.05). The integrity of feathers and integument, scored in the head/neck, wing and tail regions was repeatedly better in the EE birds compared to control birds at most investigated time points (p < 0.05), suggesting a reduction in stress related aggression by the use of the turkey tree. Head pecking, running and flying activity, foraging, and preening were overall comparable between the EE and the control group (p > 0.05). Humoral immunity as determined by vaccination-induced anti-Newcastle disease virus antibody titers, was not affected by the turkey tree use. The flow cytometric evaluation of blood monocyte and T-lymphocyte numbers showed no repeatable difference between control and EE groups. Interestingly, compared to the control groups, EE birds displayed significantly higher numbers of circulating MHC class II+ lymphocytes and lower numbers of thrombocytes at various time points compared to controls (p < 0.05). This study provides clear evidence that environmental enrichment with plateaus not only leads to an altered behavioral repertoire but also modifies some of the investigated immune parameters, implying that EE may have a modulatory effect on turkeys’ immunity and overall fitness. Further studies are needed to understand the correlation between behavior and health parameters in birds more closely.