Behavioral and Physiological Reactions to a Sudden Novel Object in the Weanling Horse: Quantitative Phenotypes for Future GWAS.
Abstract: The startle response can be defined as a reflexive reaction to the sudden appearance of a novel stimulus that influences the survival and resilience of animals. In domesticated species, the behavioral component of the startle response can, in some cases, cause serious injury to the animal or human handlers if inappropriately expressed. Here, we describe a longitudinal study in a population of stock-type horses that quantified behavioral startle responses elicited by the presentation of a sudden novel object (rapidly opening umbrella). The study was performed in weanling foals across four consecutive years ( = 74, mean age = 256 days). Behavioral assays for the startle response phenotype focused on six behavioral variables: latency to return to the feed pan (seconds), maximum distance fled (meters), proportion of time spent walking or trotting (seconds), and how long a horse spent standing facing away from or toward the novel object. We observed behavioral startle response variables in relation to cardiac response, age, and sex for each individual. Each horse's cardiac startle response pattern was determined and categorized into heart rate response cluster groups identified as accelerators and decelerators. Using principal component analysis (PCA) with a factor rotation, we identified "startle response" phenotypes that summarize the behavioral and physiological variables. The largest component of variation, Factor 1, comprised 32.5% of the behavioral variable with a positive correlation with latency and distance, and was not influenced by sex or age. Factor 2 comprised 23.2% of the variation, and was positively correlated with activity level performed such as proportion of time spent walking and/or trotting. Horses with the accelerator type cardiac response had significantly higher Factor 1 scores than decelerators but did not differ in Factor 2. Future work includes expanding our sample size to conduct a genome-wide association study (GWAS) to identify novel genetic loci influencing behavioral startle reactions using recorded behavioral and physiological phenotypes.
Publication Date: 2023-02-26 PubMed ID: 36980865PubMed Central: PMC10048014DOI: 10.3390/genes14030593Google Scholar: Lookup
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- Journal Article
- Research Support
- U.S. Gov't
- Non-P.H.S.
Summary
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The research conducts a detailed study of the startle response observed in weanling foals on exposure to a new object, in this case a rapidly opening umbrella. It identified distinct behavioral and physiological responses, with the aim of assisting future genetic studies into the traits that govern such reactions.
Understanding the Startle Response
- The reflexive reaction of an animal to the sudden appearance of a novel stimulus is termed as the startle response. It has a survival value but can also cause injuries in domesticated species if the animal expresses it inappropriately. This research aimed to quantify such responses in weanling foals, focusing on six behavioral variables which included the time taken to return to feed, maximum distance run, time spent walking or trotting, and how long the horse faced towards or away from the novel object.
Method of the Study
- The study involved assessing the behavior of 74 weanling horses over four years. Each horse’s behavior was observed in conjunction with its cardiac response, age, and sex.
- The heart rate response of each horse was categorized into accelerators and decelerators.
- The researchers then used Principal Component Analysis (PCA), a statistical procedure, to identify distinct startle response phenotypes combining behavioral and physiological variables.
Outcomes of the Research
- The researchers found that the most significant component of variation was latency and distance, contributing to 32.5% of the behavioral variable. This association was not influenced by the age or sex of the horse.
- 23.2% of the variance was associated with the activity level of the horse, for instance, the time it spent walking or trotting.
- Horses that were termed as accelerators in heart rate response showed significantly higher latency and distance scores compared to the decelerator group. There was no difference noted in activity level.
Implications and Future Research
- The data collected through this study will be used in future genome-wide association studies (GWAS) to identify the genetic factors influencing the startle response. This will help in gaining a deeper understanding of the animal’s behavior and physiological responses to unexpected stimuli.
Cite This Article
APA
Powell BB, Horvath KC, Gilliam TL, Sibille KT, Keil A, Miller-Cushon EK, Wickens CL, Brooks SA.
(2023).
Behavioral and Physiological Reactions to a Sudden Novel Object in the Weanling Horse: Quantitative Phenotypes for Future GWAS.
Genes (Basel), 14(3), 593.
https://doi.org/10.3390/genes14030593 Publication
Researcher Affiliations
- Department of Animal Sciences, University of Florida, Gainesville, FL 32611, USA.
- Department of Animal Sciences, University of Florida, Gainesville, FL 32611, USA.
- Department of Animal Sciences, University of Florida, Gainesville, FL 32611, USA.
- Departments of Physical Medicine & Rehabilitation, College of Medicine, University of Florida, Gainesville, FL 32611, USA.
- Department of Psychology and Center for the Study of Emotion & Attention, University of Florida, Gainesville, FL 32608, USA.
- Department of Animal Sciences, University of Florida, Gainesville, FL 32611, USA.
- Department of Animal Sciences, University of Florida, Gainesville, FL 32611, USA.
- Department of Animal Sciences, University of Florida, Gainesville, FL 32611, USA.
- UF Genetics Institute, University of Florida, Gainesville, FL 32610, USA.
MeSH Terms
- Humans
- Animals
- Horses / genetics
- Genome-Wide Association Study
- Longitudinal Studies
- Reflex, Startle / genetics
- Phenotype
- Genetic Loci
Conflict of Interest Statement
The authors declare no conflict of interest.
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Citations
This article has been cited 5 times.- Jafari H, Abebe BK, Cong L, Ahmed Z, Zhaofei W, Sun M, Muhatai G, Chuzhao L, Dang R. Review: Genomic insights into the adaptive traits and stress resistance in modern horses. Stress Biol 2026 Jan 12;6(1):5.
- Klitzing L, Kirsch K, Schindler M, Merle R, Hoffmann G, Thöne-Reineke C, Wiegard M. Exploring factors that influence the behavior response to novel object tests in young thoroughbred horses: investigating sex, test site and auction history. Front Vet Sci 2024;11:1478350.
- Mickle AM, Tanner JJ, Holmes U 3rd, Rashid A, Barolette O, Addison B, Sambuco N, Garvan C, Lai S, Seubert C, Schmidt S, Staud R, Edberg JC, Redden D, Goodin BR, Price CC, Fillingim RB, Sibille KT. Applying evidence-based cross-disciplinary concepts helps to explain the heterogeneity in pain, function, and biological measures in individuals with knee pain with/at risk of osteoarthritis. Pain Rep 2025 Feb;10(1):e1225.
- Mickle AM, Staud R, Garvan CS, Kusko DA, Sambuco N, Addison BR, Vincent KR, Redden DT, Goodin BR, Fillingim RB, Sibille KT. Dispositional traits help explain individual differences in relationships between a radiographic knee osteoarthritis measure, pain, and physical function. Ther Adv Musculoskelet Dis 2024;16:1759720X241235805.
- Mickle AM, Sibille KT. Deciphering relationships between stress biomarkers and fibromyalgia syndrome with implications relevant to other chronic pain conditions. Pain 2024 Jan 1;165(1):243-245.
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