Welfare indicators in laying hens
Sammanfattning: There is a growing concern regarding the welfare of laying hens worldwide and there are both ethical and economic reasons for improving their welfare. Although several different welfare indicators are used today, their ability to accurately reflect welfare status is sometimes questioned. This thesis sought to increase knowledge regarding a number of these welfare indicators by investigating whether and to what extent they were affected when layers were exposed to different stressors. Three different commercial laying hen genotypes were used and birds were challenged by being excluded either from their nests in furnished cages or from the litter area in a single-tier floor system. Excluding birds from their nests resulted in an increased stress response that was detectable in corticosterone metabolites in droppings, corticosterone concentration in egg yolk, heterophil to lymphocyte ratio and egg shell irregularities. Excluding birds from the litter area during the first two weeks in the laying facility resulted in differences in feather cover, approaches towards a novel object, tonic immobility duration and egg shell irregularities measured later in the laying period. Interestingly, according to the welfare indicators used, birds previously excluded from the litter area, and consequently deprived of litter and available area, had better welfare than non-excluded birds. In addition, levels of corticosterone metabolites in droppings were influenced by factors such as diet, genotype, bird age, cage tier, droppings mass, time of day and the kind of assay used. The results showed that several, but not all, indicators were able to detect different stress responses, suggesting that they are more or less appropriate to use depending on the situation prevailing. Many factors influenced the results obtained and there were few and inconsistent correlations, displaying a complex relationship between indicators. Overall, this indicates that welfare assessment should preferably be based on results from several indicators and that careful interpretation of the results is required before stating firm conclusions regarding laying hen welfare.
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