Background & Aims
Animal by-products are underutilized during abattoir processing of livestock. The biological data contained within this tissue can be used to gain insight into wellbeing. Identifying signals of positive and negative welfare at line speed would allow interventions to be assessed at scale. To establish this opportunity, studies are needed to demonstrate translational knowledge relevance between humans, rodents and livestock and the foundational understanding of pain neurobiology.
This case study is part of a larger cohort study aimed at quantifying cellular responses to painful husbandry procedures using central nervous system tissue histology in addition to behavioral measurement and multi-omic tissue analysis, with the goal of enabling innovative pain mitigation strategies for sheep. The case study investigates an extreme phenotype subset analysis comparing one lamb with a chronic injury and four lambs with no clinical evidence of injury but presenting varying nociceptive responses.
Methods
Five female Merino lambs were raised on farm as part of the larger cohort study. One lamb was euthanized at 10months after a chronic digital avulsion injury was identified during data collection, the other four lambs were selected from the control group of the cohort study and slaughtered at an abattoir in accordance with the larger study protocol. Production measures and behavioral and nociceptive responses were recorded at multiple intervals from marking (vaccination and ear tagging at 4-6 weeks) to slaughter. Wool steroid hormone analysis was performed using liquid chromatography-mass spectrometry. Brains collected at abattoir were formalin fixed, sectioned, and stained with haematoxylin and eosin. Several pain-associated brain regions were selected for morphological analysis, including the cingulate cortex, rostral ventromedial medulla, and somatosensory cortex. The cell types and cell density were calculated, identifying the relative abundance of neurons and glial cells.
Results
In comparison to the mean of the four control lambs, the injured lamb had greater cell density in multiple pain-related brain regions, higher cortisol levels (by 3.3 standard deviations), lower body weight (-3.5 SD) and body condition score (-4.9 SD), smaller frame size (-2.3 SD), and reduced manual nociceptive threshold (-2.4 SD). Notable brain areas with greater cell density for the injured lamb included the cingulate cortex (6.7 SD), ventrolateral (4.2 SD) and lateral (3.7 SD) periaqueductal gray, dentate gyrus granule cell layer (5.3 SD), somatosensory cortex (3.5 SD), and the nucleus raphe magnus (2.3 SD) and other regions (2.5 SD) of the RVM.
A Spearman rank correlation analysis also found a strong correlation between cortisol levels and cell density in the RVM, which was statistically significant (r = 1, p=0.017). Together, these results suggest an explanatory role for altered stress-mediated descending inhibition/facilitation pathways in the chronic pain phenotype.
Conclusions
In this small case study, we demonstrated how first-line neural histological measures may be used to identify differences in an injured sheep compared to healthy individuals. Identifying the neural signatures of chronic pain and altered stress response may aid in the development of effective pain mitigation strategies and subsequent monitoring of the adoption of such strategies in the greater livestock population.
Given the volume of animals raised and slaughtered annually for human protein consumption, there is an immense opportunity to further our understanding of the animal experience and pain neurobiology. Developing techniques to efficiently collect and analyze biological data at scale will better our ability to identify positive and negative influences on animals and ultimately improve their welfare.
References
Colditz, I. G., Smith, E. G., Ingham, A. B., & Dominik, S. (2023). Indicators of functional integrity in production animals. Animal Production Science, 63(9), 825-843. https://doi.org/10.1071/An23029
Cozzi, B., Bonfanti, L., Canali, E., & Minero, M. (2020). Brain Waste: The Neglect of Animal Brains. Front Neuroanat, 14, 573934. https://doi.org/10.3389/fnana.2020.573934
De Ridder, D., Adhia, D., & Vanneste, S. (2021). The anatomy of pain and suffering in the brain and its clinical implications. Neurosci Biobehav Rev, 130, 125-146. https://doi.org/10.1016/j.neubiorev.2021.08.013
Lubejko, S. T., Livrizzi, G., Patel, J., Yung, J. C., Yaksh, T. L., & Banghart, M. R. (2023). Inputs to the locus coeruleus from the periaqueductal gray and rostroventral medulla shape opioid-mediated descending pain modulation. bioRxiv. https://doi.org/10.1101/2023.10.10.561768
Pagliusi, M., Jr., & Gomes, F. V. (2023). The Role of The Rostral Ventromedial Medulla in Stress Responses. Brain Sci, 13(5). https://doi.org/10.3390/brainsci13050776
Weaver, S. J., Hynd, P. I., Ralph, C. R., Edwards, J. E. H., Burnard, C. L., Narayan, E., & Tilbrook, A. J. (2021). Chronic elevation of plasma cortisol causes differential expression of predominating glucocorticoid in plasma, saliva, fecal, and wool matrices in sheep. Domestic Animal Endocrinology, 74. https://doi.org/10.1016/j.domaniend.2020.106503
Presenting Author
Mark Hutchinson
Poster Authors
Charlotte Johnston
BVetBio/BVSc(Hons)
University of Adelaide
Lead Author
Daniel Barratt
BSc(Hons)
University of Adelaide. Davies Livestock Research Centre.
Lead Author
Mandi Carr
BVetSci
Univeristy of Adelaide. Davies Livestock Research Centre.
Lead Author
Vilma Hysenaj
The Australian Wine Research Institute. Metabolomics Australia
Lead Author
Carmel Maher
University of Adelaide
Lead Author
Danila Marini
BSc (Hons)
University of Adelaide. Davies Livestock Research Centre.
Lead Author
Stefan Musolino
BHlthSc (Hons)
University of Adelaide
Lead Author
Luca Nicolotti
PhD
The Australian Wine Research Institute. Metabolomics Australia
Lead Author
Wayne Pitchford
PhD
University of Adelaide. Davies Livestock Research Centre.
Lead Author
Mark Hutchinson
University of Adelaide
Lead Author
Rónán Ruggles
BPsychSc, BA(Hons), BVetBio
University of Adelaide
Lead Author
Topics
- Other