Browsing by Subject "Housing environment"

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Impact of housing environment and rearing condition on the immune system and welfare of laying hens
(2021) Hofmann, Tanja Melanie; Stefanski, Volker
In recent years, consumers’ interest in modern farm animal husbandry and, above all, criticism of intensive production systems that can impair animal welfare, have increased sharply. From hatch, chickens are confronted by a wide range of environmental and social stressors that may confound homeostasis and impair their health and welfare. Not being able to deal with the environment can lead to an activation of the stress system, resulting in a release of neuroendocrine signals like glucocorticoids. These have the potential to modify the immune system and alter species-specific behavior with possible detrimental impacts on animals’ health and welfare. In this context, early-life conditions play a special role as they were shown to have long-term consequences for physiology and behavior in the later life. High stocking densities which activate the hypothalamic-pituitary-adrenal-axis are said to be one of the largest welfare concerns in the poultry industry. Previous research has primarily focused on the effects of stocking density on broilers and adult laying hens, but few studies have focused explicitly on layer pullets, and none of them investigated long-term effects on the immune system. The understanding of short- and long-term consequences of environmental conditions during rearing on the immune system and behavior of layer pullets is essential for shaping an environment that avoids allostatic overload, thus promoting animal health and welfare. This doctoral thesis aimed to identify and evaluate potential immunomodulating factors in the housing environment of chickens. In order to achieve this, it summarizes and reviews important aspects of housing environments for the immune system in chickens. Furthermore, an existing flow cytometric method for the enumeration of leukocytes and discrimination of lymphocyte subsets in blood was adapted to lymphatic tissues. Moreover, short- and longterm consequences of stocking density during rearing on the immune system, stress hormone level and behavior in layer pullets were evaluated. The results are described in detail in three peer-reviewed manuscripts published in international journals. The literature analysis identified several housing conditions as immunomodulating factors. Light management was marked as an effective tool to modulate the immune response in chickens, as long light phases were demonstrated to lower adaptive cellular and humoral immune responses while certain light colors, especially of shorter wavelengths, promote some immune functions. Moreover, particularly high ammonia and hydrogen sulfide concentrations pose a threat to chickens’ health by dampening the adaptive immune response and promoting inflammation. However, the interaction between housing environment and management is complex. Depending on the type of housing form, chickens are confronted with different social and environmental challenges, which in turn can have an impact on the immune and stress system. An understanding of immunosuppressive risk factors is essential for successful poultry management aiming to optimize health, welfare and economic efficiency. To broaden the assessment of immune status for scientific purposes, new staining- and gating strategies for avian lymphatic tissues were adapted to an existing flow cytometric method for blood. The adaptation process showed that the application of already established protocols to other tissues is possible, but has to be examined carefully as tissue-specific effects or cell-preparative procedures might lead to differences in possible combinations of antibody-fluorochrome conjugates. The results of the experimental study within this doctoral thesis demonstrate for the first time that stocking density during rearing has not only short- but also long-term impacts on the immune system in laying hens. Pullets reared at high stocking densities showed stress-related alterations in immune cell numbers and higher incidences of feather pecking that manifest in the laying period. This highlights the significance of early-life conditions for immunocompetence throughout the whole production cycle. Of particular interest is that the number of gamma-delta T cells was lower in the high-density group, which has not been investigated in any stress-related studies with chickens before. The present doctoral thesis provides a significant contribution to the improvement of health and welfare in poultry farming and forms a basis for further research about long-lasting consequences of rearing conditions on the immune system, especially in laying hens.