Oxidative Stress: What the Research Says
Evidence from 27 peer-reviewed studies
What Professionals Should Know
- •Use gait analysis and heart rate recovery (not resting heart rate) as practical field tools to monitor if individual horses and donkeys are being overloaded
- •Multiple assessment methods—physiological, biochemical, and biomechanical—should be combined to establish safe, evidence-based load limits for working equids
- •Standardized load-carrying capacity guidelines are currently lacking and urgently needed for working equids in developing countries to improve welfare outcomes
- •Nutraceutical supplementation with antioxidants and omega-3 fatty acids may reduce exercise-induced muscle damage (lower CK) in endurance horses, potentially supporting recovery and performance
- •RBC antioxidant capacity improvements suggest enhanced cellular protection against oxidative stress during intense aerobic work, which could translate to better stamina and reduced fatigue
- •Consider recommending this type of supplement to endurance horse owners 3 weeks prior to competition or intensive training phases to optimize antioxidant status
- •High-dose IV vitamin C (100 mg/kg) may reduce circulating oxidative metabolites in horses, but clinical significance is unclear given lack of effect on other oxidative markers
- •Vitamin C appears safe for IV administration in horses with dose-dependent plasma concentration increases, but current evidence does not support routine use for improving antioxidant status in healthy animals
- •If considering vitamin C as adjunctive sepsis therapy, recognize that evidence from this healthy horse model is limited and therapeutic efficacy in septic patients remains unproven
- •Breed differences significantly affect HPA axis and metabolic hormone interpretation—reference ranges for ponies should not be extrapolated from horses, particularly for ACTH and insulin in fall months
- •Ponies show elevated insulin and ACTH in fall/winter, suggesting heightened metabolic and endocrine challenges during these seasons that may increase laminitis and metabolic disease risk
- •Consider seasonal timing when performing endocrine testing in both ponies and horses, as results vary substantially between spring and fall sampling
- •Plasma protein panels may enable objective monitoring of training adaptation and identification of overtraining syndrome in racehorses before performance decline occurs
- •Different training phases produce distinct proteomic signatures, suggesting that biomarker interpretation should account for training phase rather than using single reference values
- •These candidate biomarkers could support evidence-based decisions about training load adjustment, recovery protocols and readiness for competition in racing programs
- •Monitor antioxidant status and magnesium levels more closely in older pregnant mares (≥12 years), as age-related changes in glutathione peroxidase activity may affect their physiological reserves during late gestation and parturition
- •Parity appears less important than age in determining oxidative stress responses during pregnancy and postpartum, suggesting breeding programmes should account for maternal age over number of previous pregnancies
- •Nutritional supplementation or monitoring of magnesium and antioxidant capacity may warrant consideration in geriatric pregnant mares to support optimal maternal and fetal outcomes
- •Circus management in this study population did not appear to compromise equine mental status or create oxidative stress compared to conventional riding management, suggesting welfare concerns may be management-dependent rather than circus-inherent
- •Older horses (16+ years) require enhanced nutritional and care strategies to support antioxidant capacity, as their biological antioxidant potential declines significantly with age regardless of management type
- •Regular monitoring of antioxidant markers in aging circus and working horses may help identify susceptibility to oxidative stress and enable preventative management adjustments
- •Feeding timing before transport affects oxidative balance in horses; feeding closer to departure (1 hour) may trigger different antioxidant responses than feeding 6-12 hours prior
- •Long-distance transport (12 hours) without food or water increases oxidative stress markers even though they remain within normal ranges, suggesting subclinical effects warrant further investigation
- •Gastric ulceration risk during transport cannot be reliably predicted by oxidative stress parameters alone; additional factors beyond oxidative stress likely contribute to EGUS development
- •High-grain feeding (>50%) in meat horses compromises intestinal barrier function and increases pathogenic bacterial translocation—consider fibre-based feeding (70% forage) to improve welfare and reduce contamination risk
- •Cereal grain-based diets trigger compensatory antioxidant responses in muscle tissue, suggesting cellular stress; lower plasma catalase indicates systemic oxidative burden despite upregulation at tissue level
- •For producers of horse meat, fibre-based feeding protocols may improve food safety outcomes (reduced bacterial contamination) and overall animal welfare without necessarily compromising carcass quality
- •Horses may be more susceptible to oxidative stress than cattle due to structural differences in plasma albumin; consider antioxidant supplementation strategies in horses with oxidative stress-related conditions
- •Nutritional support targeting antioxidant systems (vitamin E, selenium, other antioxidants) may be particularly important in equine practice given the inherent limitation in plasma antioxidant defenses
- •This research supports investigation of species-specific antioxidant therapies for horses, as conventional approaches developed for other species may not fully compensate for equine albumin's methionine deficiency
- •Oiled hay feeding systems may offer a practical dietary management strategy for asthmatic horses that need to maintain forage intake
- •Soybean oil coating on mechanically processed hay mechanically reduces dust inhalation, a primary trigger for severe equine asthma
- •This approach allows horses with SEA to continue hay feeding while potentially reducing clinical exacerbations and airway inflammation
- •Replacing soybean oil with flaxseed oil in horse diets can improve metabolic and antioxidant health, potentially benefiting performance and recovery in riding horses
- •FO supplementation at 25 mL per 100 kg body weight daily supports immune function through elevated lysozyme levels and lymphocyte counts
- •The improved lipid profile and reduced oxidative stress markers suggest FO may help prevent age-related decline and support long-term health in working horses
- •Donkey owners and veterinarians should not use equine reference ranges for selenium and vitamin E assessment; donkey-specific values are lower and indicate potential species differences in nutritional requirements
- •Young donkeys (foals) show lower vitamin E concentrations than adults, warranting attention to micronutrient supplementation during growth phases
- •Establishing breed-specific reference ranges for donkeys can improve early detection and prevention of deficiency-related neurologic and muscular complications
- •Lameness in dairy cattle may be partially preventable through mineral supplementation targeting zinc, copper, and manganese to maintain hoof integrity
- •Monitoring serum antioxidant markers (SOD, metallothionein) and mineral status could help identify cattle at risk of lameness before clinical signs appear
- •Hoof quality assessment combined with mineral profiling provides a practical diagnostic approach to lameness management in dairy herds
- •Polyunsaturated oil and vitamin E supplementation can boost antioxidant defences in working horses, with GPx and SOD increases observed within 8 weeks—relevant for managing oxidative stress in athletic performance
- •Response patterns differ between resting and training horses, suggesting supplementation protocols may need tailoring based on workload; maintenance horses showed broader haematological changes
- •This nutritional intervention appears safe and supports physiological adaptation to exercise stress, making it a practical addition to feeding programmes for performance horses
- •Theileria equi infection triggers a cascade of oxidative stress markers that compromise cellular function; veterinarians should monitor for this parasite in horses showing signs of haemolysis or general malaise
- •The marked increase in free haemoglobin and oxidative damage suggests T. equi-infected horses may benefit from supportive antioxidant therapy and close monitoring of liver function
- •DNA damage detected in infected cells indicates potential for long-term health consequences; prevention through tick control and early detection via PCR screening is preferable to managing chronic infection
- •Maintaining horses at BCS <7 is associated with lower plasma insulin and reduced laminitis risk, making body weight management a practical preventive strategy
- •Overweight horses show markers of oxidative stress and dyslipidemia; regular condition scoring and feed management should be routine practice
- •Elevated insulin in obese horses is a modifiable risk factor for pasture-associated laminitis, providing actionable guidance for clients managing at-risk animals
- •Regular training increases horses' natural antioxidant defences, improving their ability to manage oxidative stress from exercise
- •Timing of exercise may interact with circadian changes in antioxidant capacity, with trained horses showing evening peaks rather than daytime peaks—relevant for scheduling demanding work
- •Monitoring antioxidant status and understanding circadian variations could inform training intensity and recovery protocols to optimise adaptation
- •Spirulina platensis supplementation may offer a complementary dietary strategy to support management of EMS horses by improving insulin sensitivity and reducing systemic inflammation
- •Weight loss coupled with improved insulin sensitivity suggests potential benefit as an adjunctive therapy alongside conventional EMS management (dietary restriction, exercise, medications)
- •Results are preliminary in vivo findings; further controlled clinical trials with defined sample sizes and control groups are needed before recommending widespread use in practice
- •Reduced plasma glutathione reductase activity appears to indicate oxidative stress in horses with small intestinal strangulation, which may influence prognosis and survival outcomes
- •Electrolyte and acid-base abnormalities (particularly bicarbonate and PaCO2) correlate with antioxidant enzyme activity in colic cases, suggesting monitoring these parameters may be clinically relevant
- •Antioxidant status may represent a measurable biomarker for oxidative stress severity in small intestinal strangulation cases, potentially aiding prognostic assessment
- •Macroalgae-based supplements show promise as natural alternatives to antimicrobial and anthelmintic drugs given emerging resistance concerns, but evidence in horses specifically remains limited
- •Seaweed's nutritional profile and bioactive compounds may support equine gastrointestinal health and welfare, though manufacturer claims require further substantiation through rigorous research
- •Until regulation and standardization improve, veterinarians should exercise caution with macroalgae supplements and recommend only those with documented safety profiles
- •Homocysteine may become a useful diagnostic marker in equine practice, but standardized reference ranges for healthy horses are needed before clinical application
- •Practitioners should be aware that elevated homocysteine may contribute to reproductive losses and cardiovascular complications, warranting further investigation in at-risk populations
- •Nutritional and metabolic management strategies targeting homocysteine metabolism could potentially improve breeding outcomes and cardiovascular health, pending further research
- •Consider species-specific differences when diagnosing endometritis in mares versus cows, as inflammatory pathways and immune responses differ substantially
- •Biomarkers related to oxidative stress in blood or uterine fluid may offer improved diagnostic tools beyond traditional microbiological testing alone
- •Inflammation management in endometritis should account for the role of RONS and their harmful by-products, suggesting antioxidant support may be relevant to therapeutic strategy
- •Consider adding vitamins E, C, and β-carotene to horses' diets during periods of physical stress, illness, or intense training to mitigate oxidative damage
- •These dietary supplements may help prevent oxidative stress-related diseases and reduce inflammation-associated tissue damage in working horses
- •Antioxidant supplementation appears most beneficial as a preventive strategy rather than treatment of established conditions
- •Obesity management in horses should be prioritized as a preventive strategy against insulin dysregulation and laminitis risk
- •Practitioners should recognize that insulin dysregulation is a key mechanism linking metabolic dysfunction to laminitis, requiring targeted dietary and management interventions
- •Understanding inflammatory pathways related to adiposity and oxidative stress may inform future therapeutic approaches for laminitis prevention and management
- •Competition-related stress induces measurable acute phase and oxidative stress responses in eventing horses; monitoring these markers may help assess recovery demands and welfare after intense events
- •Changes in lymphocyte subpopulations suggest competition temporarily alters immune cell distribution; allow adequate recovery time between events to restore baseline immune status
- •While haematological changes occurred, values remained normal; however, biochemical markers of oxidative stress may be more sensitive indicators of competition impact than standard blood parameters
- •Environmental phthalate exposure (common in plastics and consumer products) may impair mare fertility at surprisingly low concentrations; consider reproductive management strategies for mares with high environmental exposure.
- •The dose-dependent biphasic response suggests that oocyte maturation failure and cumulus cell dysfunction occur through different mechanisms, which may inform future therapeutic interventions for fertility issues.
- •Mares with DEHP-exposed oocytes that do achieve maturation retain developmental competence, but further in vivo studies are needed before drawing conclusions about breeding outcomes.
Key Research Findings
Approximately 112 million working equids in developing countries are at risk, with many associated with brick kilns and overloading-related welfare issues
Gait symmetry and stride parameter analysis are reliable markers for assessing loading capacity and adaptations to load
Heart rate recovery post-work is a superior indicator of load-carrying capacity compared to absolute heart rate values
Oxidative stress, plasma lactate, serum creatine kinase, and salivary cortisol are biochemical indicators that can assess loading ability in working equids
Dietary supplement containing natural antioxidants and omega-3 fatty acids significantly increased RBC antioxidant capacity at rest (p = 0.037) and post-exercise (p = 0.006) after 21 days of supplementation
Serum creatine kinase (CK) was significantly lower in the treatment group compared to controls at T1 (p = 0.006), indicating reduced muscle damage
Significant time*group interaction effects were observed for serum CK (p = 0.026) and RBC antioxidant capacity measurements, demonstrating supplement efficacy
The supplement appears beneficial for endurance horses undergoing intense aerobic exercise by enhancing antioxidant defense mechanisms
Ascorbic acid at 100 mg/kg decreased plasma dROM (determinants of reactive oxygen metabolites) by 63.3 units at 2 hours post-treatment (P = 0.03)
Plasma ascorbic acid concentrations increased in a dose-dependent manner across 25, 50, and 100 mg/kg doses
No significant effects of any AA dose on basal or stimulant-induced intraerythrocytic ROS, neutrophil ROS production, or plasma antioxidant capacity at any timepoint
High-dose IV ascorbic acid (100 mg/kg) showed limited antioxidant benefits in healthy horses, with only dROM reduction demonstrated
Fall plasma ACTH concentration was significantly higher in ponies compared with horses (p<0.001)
Insulin concentrations in ponies were significantly higher in fall compared with spring (p<0.001) and compared with horses in fall (p<0.001)
Total cortisol concentration was significantly lower in ponies in fall compared with spring (p=0.05)
Evidence Base
Quantifying the Impact of Mounted Load Carrying on Equids: A Review.
Bukhari Syed S U H, McElligott Alan G, Parkes Rebecca S V (2021) — Animals : an open access journal from MDPI
Antioxidant capacity and athletic condition of endurance horses undergoing nutraceutical supplementation.
Stucchi L, Rossi R, Mainardi E et al. (2025) — Journal of equine veterinary science
Effects of intravenous administration of ascorbic acid (vitamin C) on oxidative status in healthy adult horses.
Taylor Sandra D, Hart Kelsey A, Vaughn Sarah et al. (2024) — Journal of veterinary internal medicine
The Effect of Season and Breed on Hypothalamic-Pituitary-Adrenal Axis Hormones, Metabolic Hormones, and Oxidative Markers in Ponies and Horses.
Vaughn Sarah Alison, Lemons Margaret B, Hart Kelsey A (2025) — Journal of veterinary internal medicine
Exercise-specific plasma proteomic signatures in racehorses: Candidates for training adaptation and peak load monitoring.
Grzędzicka Jowita, Świderska Bianka, Sitkiewicz Ewa et al. (2025) — Equine veterinary journal
Does age and parity affect the oxidative profile of pregnant and postpartum mares?
Rosa Filho R R, França D S, Alonso M A et al. (2025) — Journal of equine veterinary science
Assessing the Peripheral Levels of the Neurotransmitters Noradrenaline, Dopamine and Serotonin and the Oxidant/Antioxidant Equilibrium in Circus Horses.
Cocco Raffaella, Sechi Sara, Rizzo Maria et al. (2024) — Animals : an open access journal from MDPI
Effects of Transport and Feeding Strategies Before Transportation on Redox Homeostasis and Gastric Ulceration in Horses.
Gharehaghajlou Yashar, Raidal Sharanne L, Freccero Francesca et al. (2023) — Journal of equine veterinary science
A Fibre- vs. cereal grain-based diet: Which is better for horse welfare? Effects on intestinal permeability, muscle characteristics and oxidative status in horses reared for meat production.
Raspa Federica, Dinardo Francesca Rita, Vervuert Ingrid et al. (2022) — Journal of animal physiology and animal nutrition
Relative Deficiency in Albumin Methionine Content is Associated With Decreased Antioxidant Capacity of Equine Plasma.
Sanz Macarena G, Schnider Darren R, Mealey Katrina A (2021) — Journal of equine veterinary science
Effects of a propriety oiled mixed hay feeding system on lung function, neutrophilic airway inflammation and oxidative stress in severe asthmatic horses.
Jochmans-Lemoine Alexandra, Picotte Khristine, Beauchamp Guy et al. (2020) — Equine veterinary journal
Effect of Dietary Flaxseed Oil Supplementation on the Redox Status, Haematological and Biochemical Parameters of Horses' Blood.
Sembratowicz Iwona, Zięba Grzegorz, Cholewinska Ewelina et al. (2020) — Animals : an open access journal from MDPI
Selenium and Vitamin E Concentrations in a Healthy Donkey Population in Central Italy.
Bazzano Marilena, McLean Amy, Tesei Beniamino et al. (2019) — Journal of equine veterinary science
Oxidative stress and imbalance of mineral metabolism contribute to lameness in dairy cows.
Zhao, Wang, Wang et al. (2016) — Biological trace element research
Antioxidant and haematological biomarkers in different groups of horses supplemented with polyunsaturated oil and vitamin E.
Mélo S K M, Diniz A I A, de Lira V L et al. (2016) — Journal of animal physiology and animal nutrition
Oxidative stress and DNA damage in horses naturally infected with Theileria equi.
Radakovic M, Davitkov D, Borozan S et al. (2016) — Veterinary journal (London, England : 1997)
Adiposity, plasma insulin, leptin, lipids, and oxidative stress in mature light breed horses.
Pleasant R S, Suagee J K, Thatcher C D et al. (2013) — Journal of veterinary internal medicine
Training-induced modifications of circadian rhythmicity of peroxidative parameters in horses.
Piccione G, Giannetto C, Marafioti S et al. (2012) — Journal of animal physiology and animal nutrition
Spirulina platensis Improves Mitochondrial Function Impaired by Elevated Oxidative Stress in Adipose-Derived Mesenchymal Stromal Cells (ASCs) and Intestinal Epithelial Cells (IECs), and Enhances Insulin Sensitivity in Equine Metabolic Syndrome (EMS) Horses
D. Nawrocka, K. Kornicka, Agnieszka Śmieszek et al. (2017) — Marine Drugs
Clinical Research Abstracts of the British Equine Veterinary Association Congress 2015.
Bardell D A, Archer D C, Milner P I (2015) — Equine veterinary journal
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A review of current and potential applications of macroalgae to equine veterinary science.
Warren P, Mc Crudden D, O'Reilly S et al. (2026) — Journal of equine veterinary science
Homocysteine-Potential Novel Diagnostic Indicator of Health and Disease in Horses.
Gołyński Marcin, Metyk Michał, Ciszewska Jagoda et al. (2023) — Animals : an open access journal from MDPI
Relationship between Oxidative Stress and Endometritis: Exploiting Knowledge Gained in Mares and Cows.
Boni Raffaele, Cecchini Gualandi Stefano (2022) — Animals : an open access journal from MDPI
Dietary Supplements of Vitamins E, C, and β-Carotene to Reduce Oxidative Stress in Horses: An Overview.
Garcia Erendira Itzel Ceja, Elghandour Mona M M Y, Khusro Ameer et al. (2022) — Journal of equine veterinary science
From Table to Stable: A Comparative Review of Selected Aspects of Human and Equine Metabolic Syndrome.
Ragno Valentina M, Zello Gordon A, Klein Colby D et al. (2019) — Journal of equine veterinary science
Effects of competition on acute phase proteins and lymphocyte subpopulations - oxidative stress markers in eventing horses.
Valle E, Zanatta R, Odetti P et al. (2015) — Journal of animal physiology and animal nutrition
In vitro acute exposure to DEHP affects oocyte meiotic maturation, energy and oxidative stress parameters in a large animal model.
Ambruosi Barbara, Uranio Manuel Filioli, Sardanelli Anna Maria et al. (2011) — PloS one