Neuroendocrine Profiles of Pekin Ducks Associated with Positive and Negative Affective States
Creators: name: Bergman, Melanie M
name: Fraley, Gregory S.
name: Alex Pasternak, J.
name: Schwean-Lardner, Karen
name: Karcher, Darrin
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 300306
subject: Animal welfare
classificationCode: 300302
subject: Animal management

description: The Pekin duck, a major poultry product, is an important livestock species that requires further study to understand their physiological needs and welfare. Welfare improvements can be obtainable by measuring a duck’s response to its environment and developing management practices that allow ducks to explore positive natural behaviors and minimize negative affective states. Assessing welfare includes measuring physical and mental states of an animal and how it copes with its environment. This thesis sets out to use established indicators for mental state, such as serotonin (5-HT) and dopamine (DA), to validate methods of measuring duck affective state applied to environment changes. Affective states can be assessed using neurotransmitter concentrations inserted into turnover equations to understand serotonergic and dopaminergic activity within the synapse. Similarly, gene expression can be linked to affective state by investigating the rate-limiting enzyme in 5-HT and DA synthesis. Developing neuroendocrine profiles for the Pekin duck can elucidate how environmental changes affect physiology and welfare. Preening cups are a semi open water source placed within duck barns to improve welfare and allow for positive natural behaviors. Since ducks are waterfowl, many believe these birds need access to open water to develop naturally and have positive welfare. Our lab designed an experiment, referenced in Chapter 3, to compare ducks raised with preening cups to ducks raised with only water nipple lines. At Purdue Animal Science Research and Education Center (ASREC), 260 grow-out Pekin ducks were raised to the industry standard. There were 2 pens that had access to preening cups on day 18 and 2 pens had access to only nipple lines. We collected duck brains on day 18 before preening cup placement (PRE, n = 6). On day 43, we collected duck brains from pens with preening cups (PC, n = 6) and from pens without preening cups (CON, n = 6). Then, brains were hemisected and further dissected into caudal mesencephalon (CM), rostral mesencephalon (RM), diencephalon (DI), and forebrain (FB). The right portions of each brain were used to investigate neurotransmitter concentrations and turnover using mass spectrometry. While the left portions were used to investigate gene expression of tryptophan hydroxylase (TPH1, TPH2) and tyrosine hydroxylase (TH). Our results found no significant differences in 5-HT turnover or 5-HT static levels associated with preening cups across collection days. In the CM, we found a decrease in DA turnovers for PC and CON (p = 0.0067) when compared to PRE. Also, we found a decrease in DA turnover for PC when compared to PRE and CON (p = 0.003) in the RM. In the CM, we found increases in TPH1 expression (p = 0.022) for PC and CON when compared to PRE and in TH expression (p = 0.022) for CON when compared to PRE. There were no significant differences found in the RM and DI brain areas for gene expression. In the FB, we found a decrease in TH gene expression (p = 0.031). Overall, our data highlights an increase in dopaminergic activity within the midbrain. This increase in DA can be correlated with aggressive behavior witnessed from ducks housed with preening cups. Elevated DA is associated with addiction and resource guarding. In this experimental study, we concluded that preening cups placed with a small number of ducks (n = 65 ducks per preening cup) may elicit aggressive behavior and decrease welfare. The results of this initial study led us to the question of how a duck affective state is altered by preening cups in a large commercial setting. A commercial Pekin duck barn will place one preening cup for approximately 1,000-1,500 ducks, which means a barn will carry about 3-5 preening cups. Similar methodology was used in Chapter 4 to investigate the ducks affective state using mass spectrometry and qRT-PCR to assess 5-HT and DA activity within the brain. We visited four commercial duck barns with an average of 7,500 ducks on day (d)21 prior to preening cup placement, d28 one week after preening cup placement, and d35 one day prior to processing. We collected litter samples to test moisture content (n = 3/barn/day) and found no differences before or after preening cup placement. We performed a transect walk by moving systematically through each barn and recording the frequency of welfare concerns. All barns showed low percentages of welfare concerns while differences were likely due to natural aging of ducks in a production system. Brains were collected from two locations in the barn including ducks actively using the preening cup (PC) and ducks across the barn not actively performing any behaviors other than standing or sitting (CON). Brains were divided into CM, RM, and DI brain areas and each half was assessed with 5-HT and DA turnover along with TPH1, TPH2, and TH gene expression. No differences were found for 5-HT turnover or static levels. This suggests that preening cups are not altering affective state. DA turnover was decreased in the CM (p &lt; 0.05) and DI (p &lt; 0.001) due to age, but no differences were found between collection location (PC vs CON). We link this increase in dopaminergic activity to natural aging and preparation for puberty as no aggressive behavior was witnessed in commercial barns. Aggression and resource guarding of commercial preening cups is unlikely due to the increased number of ducks per water source and the large space the ducks can access. There was increased TPH1 expression within the RM brain area for d35 ducks when compared to d28 and d21. We conclude that affective state is not variable within the barn based on collection locations. Overall, 5-HT was not affected by preening cups and DA was affected by age. This means that preening cups may not improve affective state and welfare, but they also do not cause determinantal effects either. Another major welfare concern associated with environment is transportation for Pekin ducks. To assess how affective state is altered by crating and transportation of hens and drakes, Chapter 5 used similar methodology as the previous studies. Transportation may cause an acutely stressful event while activating a physiological stress response. Chapter 5 measured several central and peripheral physiological parameters to assess responses to transportation. Thirty-six, 23-week-old breeder ducks from a commercial facility were randomly assigned to one of three treatment groups. The control group (CON) was caught and immediate euthanized in the pen, the crate group (CRA) was caught and crated for 90 minutes before euthanasia, and the transport group (TRA) was caught, crated, and loaded into the back of a truck to be driven on country roads at 55 mph for 90 minutes before immediate euthanasia. Blood was collected for corticosterone ELISA analysis and blood smear heterophil to lymphocyte ratio (HLR) analysis. We found that hens showed an increase in HLR (p = 0.035) and serum corticosterone (p = 0.01) due to CRA. Drakes and hens showed an increase in HLR (p = 0.035) and serum corticosterone (p = 0.0084) for TRA. These results suggest that transportation is a stressor that elicits a sex dependent response where hens increase corticosterone and HLR under CRA unlike drakes who only showed a stress response under TRA. Likewise, a sex difference was shown for 5-HT turnover where hens show a stepwise increase from CON to CRA (p = 0.01) and from CRA to TRA (p = 0.016) in the CM and RM. There were no differences for DA turnover while TPH1 gene expression was decreased (p = 0.03) for TRA hens when compared to CON and CRA hens. Our results suggest that transportation negatively shifts affective state by increasing stress responses in ducks and reducing serotonergic activity in hens. In the future, care should be taken to evaluate stress between sexes and minimize transportation time. In conclusion, preening cups and transportation are important aspects of a Pekin ducks’ life that alter affective state and physiology. We recommend proper management of preening cups to ensure positive welfare by placing water sources over open pits to prevent excess accumulation of water in the barn. We recommend that while evaluating stressors, researchers need to assess different sexes and collection time from the onset of the stressor. Future studies can include determining affective state for other enrichments such as environmental enrichment devices or investigating commercial barns without preening cups during the production cycle. Continued research could measure affective state following shorter transportation stress or chronic stress to resolve what timeframes alter 5-HT and DA turnover. Transportation may be minimized by installing on-site processing facilities to stun and process animals without transportation to reduce negative affective states. In an academic setting, pharmaceutical intervention may be interesting to investigate to improve affective state during stressful events.