Happy Chickens: Novel Physiological and Behavioral Measures of Cumulative Experience in Broilers and Laying Hens

Conventional housing environments for broiler chickens and commercial laying hens are often barren, high-density environments with an emphasis on production efficiency. These housing conditions limit birds' ability to display species-specific behaviors, can negatively impact health, and may contribute to negative cumulative experience. Cumulative experience is the culmination of all positive and negative experienced during an animal's lifetime. However, cumulative experience is difficult to quantify, as no validated measures of cumulative experience exist. Additionally, existing measures of negative animal experience mostly rely on interpretations of animal behavior which can be subjective, time consuming, and difficult to interpret. Therefore, there is scientific need for objective measures that can detect cumulative experience in poultry. Secretory and plasma Immunoglobulin A (IgA), telomere length, feather corticosterone concentrations, and attention bias testing all seem to respond to positive and negative experiences in humans or other non-human animal species, indicating that they may be useful as measures for poultry. Therefore, the objective of this thesis was to determine if these novel measures could be used as indicators of cumulative experience in broiler chickens and laying hens. In chapter 3, secretory and plasma IgA concentrations were measured in broilers raised in either high-complexity or low-complexity environments under either high or low stocking density over three replicated experiments. Birds housed in highly complex environments showed higher concentrations of plasma IgA compared to birds housed in low-complexity environments at day 48 of age, indicating reduced chronic stress in the former. Additionally, day 48 secretory IgA concentrations were decreased in birds housed in high-density environments compared to birds housed in low density environments, indicating birds from high-density environments were more chronically stressed. In chapter 4, gonad and kidney telomere length was measured to determine cumulative experience in broilers raised in the same housing conditions and replicated experiments of chapter 3. Treatment did not impact gonad telomere length, in line with expectations as gonads contain stem cells which produce high concentrations of telomerase. Birds housed in high-complexity pens had longer kidney telomeres compared to birds in low-complexity pens, indicating high-complexity birds had more positive cumulative experience. Stocking density did not impact kidney telomere length. In chapter 5, attention bias, tonic immobility, plasma and secretory IgA concentrations, and feather corticosterone concentrations were determined in laying hens raised in conventional cages or enriched floor pens. Birds in enriched floor pens showed increased attention bias, decreased tonic immobility, increased secretory IgA concentrations at week 22 of age, and decreased feather corticosterone concentrations compared to caged hens. These results indicate that compared to conventional cages, enriched pens in this study improved immune systems, reduced chronic stress, reduced fear, but increased anxiety in hens. In conclusion, secretory and plasma IgA and telomere length show appropriate contrast in response to broiler chicken housing conditions. However, additional work needs to be done before these measures can be widely used as measures of cumulative experience in poultry. Furthermore, attention bias, secretory IgA, and feather corticosterone showed an appropriate contrast between chronic stress responses in laying hens, but confirmation is needed in other contexts. Overall, the results indicate a beneficial relationship between environmental complexity and poultry welfare physiology and affective state, with the exception for anxiety in laying hens. Thus, providing an enriched environment can improve the welfare of commercial poultry and result in positive cumulative experience in most situations. Additionally, these results indicate that stocking density is a negative environment in broilers but potentially less intense than previously thought under experimental conditions. The assessment of behavioral and physiological measures of cumulative and positive animal experience should be included in experiments seeking to determine the impacts of environmental or management conditions to determine the broader impacts on poultry welfare.