Associations between postrace atrial fibrillation and measures of performance, racing history and airway disease in horses.

BACKGROUND: Atrial fibrillation (AF) is the most common performance limiting arrhythmia in racehorses. High dose exercise and airway disease promote AF in humans. Few studies have investigated epidemiological factors associated with AF in horses. OBJECTIVES: Explore variables relating to performance, exercise volume and postrace endoscopic findings in horses with AF. ANIMALS: A total of 164 horses with poor race performance and postrace AF were compared to 321 horses with poor performance without AF (PP) and 314 horses performing to expectation (TE). METHODS: Horse-level and race-level variables for horses racing in Australia and Hong Kong from 2009 to 2021 were compared using univariable and multivariable logistic regression. Postrace endoscopic exercise-induced pulmonary hemorrhage (EIPH) and tracheal mucus accumulation (TMA) grades for AF and PP horses were compared using chi-squared analysis. RESULTS: Variables that were significant in the multivariable model of AF compared to TE were distance (lengths) behind the winner, (odds ratio [OR]; 95% confidence interval [95% CI], 1.41 [1.32-1.51], P < .0001), cumulative prize money per start before the event (OR [95% CI] 1.02 [1.01-1.03], P = .01) and age (OR [95% CI] 0.72 [0.55-0.92], P = .01). More AF horses had EIPH grade ≥ 3 (23/109; 21.1%) than PP horses (7/213; 3.3%; OR [95%CI] 7.9 [3.3-20.2], P < .0001). CONCLUSIONS AND CLINICAL IMPORTANCE: Acute race performance was substantially impaired by AF but career earnings before the event were not inferior. Exercise volume did not promote AF. Higher grades of EIPH found in AF horses suggests a mechanistic relationship between these conditions.

Differentiation of equine mesenchymal stem cells into cells of osteochondral lineage: potential for osteochondral tissue engineering.

Damage to the hyaline cartilage of the joint surface and osteochondral fractures are key factors leading to the development of osteoarthritis in racehorses, representing a significant cause of racehorse retirement. To tissue-engineer an osteochondral unit that is suitable for joint repair, incorporation of a zone of calcified cartilage should be considered so as to mimic itsin vivocounterpart. To date, equine mesenchymal stem cells (eMSCs) have been reported to have multilineage differentiation potential. Yet the generation of a zone of calcified cartilage using eMSCs has not been reported. This work is an initial attempt to generate a zone of calcified cartilage using eMSCs as the single source of cells and collagen as the scaffolding material. Main advantages of using eMSCs over equine deep zone chondrocytes for the generation of a zone of calcified cartilage include no donor site morbidity and their ease of expansion in culture. Initially, we fabricated cartilage-like tissues and bone-like tissuesin vitroby differentiating eMSCs toward chondrogenic and osteogenic lineages for 21 d, respectively. We then aggregated the cartilage-like and bone-like tissues together with a layer of undifferentiated eMSCs-collagen gel in between to generate a 3-layer osteochondral unit. A zone of calcified cartilage was found between the cartilage-like and bone-like layers after a 14-day culture in chondrogenic differentiation medium. These results provide a solution toward tissue engineering of equine osteochondral units with interfacial zone without using chondrocytes harvested from the deep zone of healthy articular cartilage, and contribute to the future development of osteochondral tissue engineering strategies for human cartilage injuries in the long run.

Incidence, recurrence, and outcome of postrace atrial fibrillation in Thoroughbred horses.

BACKGROUND: Atrial fibrillation (AF) impacts performance and horse and jockey safety. Understanding the outcomes of AF identified postrace will better inform regulatory policy. HYPOTHESIS/OBJECTIVES: To investigate the outcomes after episodes of AF identified postrace and determine whether affected horses are at increased risk of additional episodes compared to the general racing population. ANIMALS: Total of 4684 Thoroughbred racehorses. METHODS: Race records for Thoroughbred horses racing in Hong Kong from 2007 to 2017 were reviewed. Horses that performed below expectation were examined by cardiac auscultation and ECG. Incidence and recurrence of AF were compared between horses with and without a history of AF and between horses with paroxysmal and persistent episodes using Fisher's exact test. RESULTS: There were 96 135 race starts during the study. Atrial fibrillation was identified in 4.9% of horses, with an overall incidence of 2.7 episodes per 1000 starts. The incidence of AF in horses after any previous episode (12.8 per 1000 starts) was higher than for horses with no previous episode (2.4 per 1000 starts; odds ratio [OR], 5.3; 95% confidence interval [CI], 3.8-7.6). Recurrence was seen in 64% of horses previously treated for persistent AF, which was higher than recurrence in horses with paroxysmal AF (23%; OR, 5.9; 95% CI, 1.6-21.2). Median duration between episodes was 343 days (range, 34-1065). CONCLUSIONS AND CLINICAL IMPORTANCE: Thoroughbreds are at increased risk of recurrent AF after both paroxysmal and persistent episodes, but the duration of time between episodes varies widely. These findings support a substantial burden of AF among individual Thoroughbred racehorses.