1. Summary
Rebecca Lindenwald
Fitness for Turkeys – Impacts of environmental enrichment on animal health and welfare
Under commercial turkey housing conditions pecking, which leads to suffering of injured birds and subsequently to economic losses, may be observed. Preventive strategies may involve environmental enrichment (EE). It is known that injurious pecking occurs as a reaction to stress, which can be caused, among other conditions, by sudden temperature shifts, periods of insufficient feeding or suboptimal lighting.
Turkeys in commercial housing systems have very few possibilities to cope with stress.
Since wild turkeys are known to use trees during the nights, it can be assumed that elevated sleeping positions would contribute to the reduction of stress also in commercial turkeys.
Physiologically, stress is associated with elevated glucocorticoid levels which may modulate the immune system. Environmental enrichment promotes the activity of the animals and thereby leads to the release of myokines that are known to also modulate immune reactions. Therefore the evaluation of effects of environmental enrichment should not only consider animal behavior, but also animal health and immune parameters in a holistic approach. However, the possibilities for monitoring immune functions in turkeys are limited, since most methods in poultry are established for chicken and only deployable for this specific species.
The aims of the first study were to establish an automated system for blood cell counting by using flow cytometry and to quantify the impact of additional factors, such as the age of the animals, the used stable or the season of the year.
Therefore, commercially available monoclonal antibodies against chicken leucocytes were tested for cross reactivity with turkey blood cells. Since the pan leucocyte marker
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against chicken CD45 used for flow cytometric blood cell counting in chicken shows no cross reactivity with turkey leucocytes, the mouse anti chicken CD44 antibodies were tested as an alternative. Its application led to the identification of cell clouds characteristic for the respective leucocyte subpopulations such as monocytes, lymphocytes and granulocytes. Additionally, the mouse anti chicken MHC class II, mouse anti chicken CD4, mouse anti chicken CD8 and mouse anti human CD51/61 antibodies showed cross reactivity with the respective blood cells of turkeys, as was verified by flow cytometric assisted cell sorting (FACS) and subsequent microscopical evaluation. Therefore, this approach allowed the detection of MHC class II positive lymphocytes, CD4+ and CD8+ T-cells, granulocytes as well as thrombocytes in diluted turkey blood. The three subgroups of granulocytes (eosinophils, heterophils and basophils) however could not be distinguished due to the lack of specific monoclonal antibodies. To investigate possible influencing factors on the concentrations of different blood cell populations, three animal trials in consecutive years were conducted. One or two groups of 22 non – beak trimmed female turkeys were housed in each trial. At five time points, including days 23, 43, 60 and 88 post hatches, automated blood cell counts were carried out. Age had a significant influence on cell numbers of the different leucocyte populations (p ≤ 0.05). Likewise, the trial was noted as an influencing factor possibly mediated through seasonal variations (p ≤ 0.05).
Aim of the second study was to investigate the impact of a self-designed environmental enrichment object with three different levels, named ‘turkey tree’, on animal behavior and animal health. Therefore, the first objective was to quantify the use of the tree by the turkeys. Based upon this, the second objective was to determine the impact on animal behavior, which was quantified using video records. Additionally, feather and integument scorings were obtained at different ages. The third objective was to assess the influence of the turkey tree on immune parameters. Therefore the antibody titers against Newcastle Disease Virus (NDV) after life vaccination, blood leucocyte and thrombocyte counts as well as serum corticosterone levels were evaluated at the age of 23, 43, 60 and 88 days post hatches.
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In all three trials the turkeys showed increasing use of the turkey tree up to the age of thirty days, with the highest daily average of 60% of the birds in the group sitting or standing on the tree. After the age of 58 days the percentage of birds that were counted on the tree decreased. In all three trials the turkey tree group showed significantly less feather pecking in comparison to the control group (p ≤ 0.05). Losses of feathers and integument lesions in the wing and tail regions were repeatedly lower in the turkey tree group in comparison to the control group during the second and third animal trials (p ≤ 0.05).
Only in the head and neck regions the turkey tree group showed more severe feather losses and lesions in comparison to the control group at three time points (p ≤ 0.05).
No repeatable significant differences in serum corticosterone levels or antibody titers were observed between the groups (p ≤ 0.05). Repeatedly higher concentrations of MHC class II positive lymphocytes per microliter full blood were noted in the turkey tree group in comparison to the control group (p ≤ 0.05). CD4+ cells as well as CD8+ T-cells showed no significant differences between the groups or inconsistent tendencies during the three trials (p > 0.05). Thrombocyte counts per microliter full blood were higher in the control group in comparison to the turkey tree group at days 43 or 60 during all three trials (p ≤ 0.05).
Therefore, this study clearly shows that the used environmental enrichment object led to lower pecking behavior, and overall less injuries and lesser feather losses in comparison to the control group. Associated with the lower pecking activity, the turkey tree group showed lower numbers of circulating thrombocytes and higher numbers of MCH class II positive lymphocytes, despite the absence of significant differences in serum corticosterone levels between the groups.
Overall, this work provides clear evidence that environmental enrichment can influence immune parameters as well as animal behavior and therefore might affect animal health. The strongest impact was noted for MHC class II positive lymphocytes, which may be associated with a stronger immune response and improved animal health.
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The elevated thrombocyte concentrations in the control group in comparison to the turkey tree group resemble conditions found in humans who are diagnosed with psychiatric disorders such as depression and obsessive compulsive disorder. It cannot be ruled out that the elevated concentrations of thrombocytes in the control group are symptoms of increased stress, and that the turkey tree may be a suitable intervention approach. These studies provide important information to be used in further studies to understand the association and interaction between EE, stress coping animal behavior and animal health.
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