A one-health lens offers new perspectives on the importance of endocrine disorders in the equine athlete

Endocrine disorders are associated with joint pain and tendon injury in humans, but the effects in the horse are only starting to be understood. Similar patterns of clinical signs and injury appear to affect horses and humans for both orthopedic and endocrine disorders, supporting the use of a one-health approach to tackle these issues. In this Currents in One Health, we will discuss common equine endocrinopathies, current testing recommendations, dietary management, genetic predispositions, and endocrine disorders' effects on performance. Our aim is to use a one-health lens to describe current comparative research so that veterinarians can employ cutting-edge preventative, diagnostic, and therapeutic recommendations. Identified key gaps in knowledge include whether equine metabolic osteoarthritis exists, if steroid joint injections are safe in horses with endocrine disorders, and if the return to performance percentage improves with concurrent treatment of endocrine and musculoskeletal disorders. Key takeaways include that the relationship between endocrine disorders and musculoskeletal disease in the horse goes beyond laminitis to include lameness, muscle atrophy, suspensory ligament degeneration, osteochondritis dissecans, and potentially metabolic osteoarthritis. Approaches learned from human and equine comparative studies can offer insight into injury recognition and management, thus mitigating the impact of endocrine disorders on performance in both species. Readers interested in an in-depth description of current and future research involving pathophysiology, novel interventions, and multiomic approaches to identify individuals with athletic limitations induced by endocrine disorders are invited to read the companion Currents in One Health by Manfredi et al, AJVR, February 2023.

A one-health approach to identifying and mitigating the impact of endocrine disorders on human and equine athletes

Endocrinopathies affect multiple species in ever-increasing percentages of their populations, creating an opportunity to apply one-health approaches to determining creative preventative measures and therapies in athletes. Obesity and alterations in insulin and glucose dynamics are medical concerns that play a role in whole-body health and homeostasis in both horses and humans. The role and impact of endocrine disorders on the musculoskeletal, cardiovascular, and reproductive systems are of particular interest to the athlete. Elucidation of both physiologic and pathophysiologic mechanisms involved in disease processes, starting in utero, is important for development of prevention and treatment strategies for the health and well-being of all species. This review focuses on the unrecognized effects of endocrine disorders associated with the origins of metabolic disease; inflammation at the intersection of endocrine disease and related diseases in the musculoskeletal, cardiovascular, and reproductive systems; novel interventions; and diagnostics that are informed via multiomic and one-health approaches. Readers interested in further details on specific equine performance conditions associated with endocrine disease are invited to read the companion Currents in One Health by Manfredi et al, JAVMA, February 2023.

The Safety and Efficacy in Horses of Certain Nutraceuticals that Claim to Have Health Benefits

Equine nutraceuticals are promoted as useful therapies to help optimize health and athletic performance, often without the benefit of independent research to support product efficacy and safety. This review focuses on 4 main categories of equine supplements that are frequently used as nutraceuticals: (i) supplements to support metabolic health, (ii) gastric support products, (iii) common ingredients that are included in supplements designed to support hoof health, and (iv) supplements to support joint health.

Evaluation of an oral joint supplement on gait kinematics and biomarkers of cartilage metabolism and inflammation in mature riding horses

Twenty stock-type horses (589 ± 126 kg BW; 13 ± 8 yr) were used in a completely randomized design for 28-d to evaluate the impact of a joint supplement on gait kinematics, inflammation, and cartilage metabolism. Horses were stratified by age, sex, body weight (BW), and initial lameness scores and were randomly assigned to one of two dietary treatments consisting of either a 100-g placebo top-dressed daily to 0.6% BW (as-fed) commercial concentrate (CON; n = 10; SafeChoice Original, Cargill, Inc.), or an oral joint supplement (SmartPak Equine LLC) containing glucosamine, chondroitin sulfate, hyaluronic acid, methylsulfonylmethane, turmeric, resveratrol, collagen, silica, and boron (TRT; n = 10). Horses were group-housed with ad libitum access to coastal bermudagrass hay (Cynodon dactylon) and allowed to graze pasture 2 h/d. Horses were exercised progressively 4 d/wk at 45 min each. On days 13 and 27, blood was harvested followed by a 19.3-km exercise stressor on concrete. Horses traveled at the walk, with no more than 15 min at the trot. Every 14 d, BW and BCS were recorded, and blood was collected for plasma prostaglandin E2 (PGE2), serum collagenase cleavage neopeptide (C2C), carboxypropeptide of type II collagen (CPII), and chondroitin sulfate 846 epitope (CS846) analysis. Kinematic gait analysis was performed every 14 d (Kinovea v.0.8.15) to determine stride length (SL) and range of motion (ROM) of the knee and hock at the walk and trot. Data were analyzed using PROC MIXED of SAS. All horses increased BW and BCS over time (P ≤ 0.01). Hock ROM increased in TRT horses (P ≤ 0.02) at the walk and tended to increase at the trot compared to CON (P = 0.09). At the walk, SL and knee ROM increased over time, independent of dietary treatment (P ≤ 0.01); no time effect was observed at the trot (P > 0.15). Regardless of treatment, C2C and CPII increased over time (P ≤ 0.05) and no effect was observed for CS846 or PGE2 (P > 0.12). In response to the exercise stressor, CPII and PGE2 decreased (P ≤ 0.05) from day 13 to 14, and CS846 and PGE2 tended to decrease (P ≤ 0.10) from day 27 to 28, independent of dietary treatment. In conclusion, hock ROM at the walk and trot was most sensitive to dietary treatment. Supplementation did not alter biomarker concentration of collagen metabolites or systemic inflammation in the 28-d period, but a future study utilizing arthrocentesis may be warranted to specifically evaluate intra-articular response to dietary treatment.

Effects of Orally Administered Resveratrol on TNF, IL-1β, Leukocyte Phagocytic Activity and Oxidative Burst Function in Horses: A Prospective, Randomized, Double-Blinded, Placebo-Controlled Study

Resveratrol, a phytophenol, is a commonly used equine nutraceutical supplement touted to exert anti-inflammatory effects. The effect of orally administered resveratrol on tumor necrosis factor (TNF), interleukin-1β (IL-1β), leukocyte phagocytic activity or oxidative burst function have not been reported in horses. The objective of this study was to determine the effects of a commercially available, orally administered resveratrol product on innate immune functions in healthy adult horses. Whole blood was collected from 12 horses prior to and following 3 weeks of treatment with either the manufacturer’s recommended dose of resveratrol or placebo. Phagocytosis, oxidative burst and pathogen associated molecular pattern (PAMP) motif-stimulated leukocyte production of TNF and IL-1β were compared pre- and post-treatment between treatment groups. Phagocytosis and oxidative burst capacity were evaluated via flow cytometry. Tumor necrosis factor and IL-1β were measured using cytotoxicity and ELISA assays, respectively. There were no significant differences in phagocytosis, oxidative burst or stimulated TNF or IL-1β production between resveratrol and placebo treatment groups. Orally administered resveratrol at a routinely recommended dose for a duration of 3 weeks did not significantly affect phagocytic activity, oxidative burst function or PAMP-stimulated leukocyte cytokine production.

Association of sustained supraphysiologic hyperinsulinemia and inflammatory signaling within the digital lamellae in light-breed horses

Background

Hyperinsulinemia is associated with equine laminitis, and digital lamellar inflammation in equine metabolic syndrome‐associated laminitis (EMSAL) is modest when compared with sepsis‐associated laminitis.

Objectives

To characterize digital lamellar inflammation in horses in a euglycemic‐hyperinsulinemic clamp (EHC) model of laminitis.

Animals

Sixteen healthy adult Standardbred horses.

Methods

Prospective experimental study. Horses underwent EHC or saline infusion (CON) for 48 hours or until the onset of Obel grade 1 laminitis. Horses were euthanized, and digital lamellar tissue was collected and analyzed via polymerase chain reaction (pro‐inflammatory cytokine and chemokine genes—CXCL1, CXCL6, CXCL8, IL‐6, MCP‐1, MCP‐2, IL‐1β, IL11, cyclooxygenases 1 and 2, tumor necrosis factor alpha [TNF‐α], E‐selectin, and ICAM‐1), immunoblotting (phosphorylated and total signal transducer and activator of transcription 1 [STAT1], STAT3, and p38MAPK), and immunohistochemistry (markers of leukocyte infiltration: CD163, MAC387).

Results

Lamellar mRNA concentrations of IL‐1β, IL‐6, IL‐11, COX‐2, and E‐selectin were increased; the concentration of COX‐1 was decreased; and concentrations of CXCL1, CXCL6, MCP‐1, MCP‐2, IL‐8, TNF‐α and ICAM‐1 were not significantly different in the EHC group compared to the CON group (P ≤ .003). Lamellar concentrations of phosphorylated STAT proteins (P‐STAT1 [S727], P‐STAT1 [Y701], P‐STAT3 [S727], and P‐STAT3 [Y705]) were increased in the EHC group compared to the CON group, with phosphorylated STAT3 localizing to nuclei of lamellar basal epithelial cells. There was no change in the lamellar concentration of P‐p38 MAPK (T180/Y182), but the concentration of total p38 MAPK was decreased in the EHC samples. There was no evidence of notable lamellar leukocyte emigration.

Conclusions and Clinical Importance

These results establish a role for lamellar inflammatory signaling under conditions associated with EMSAL.