FREE SHIPPING over $40
OVER 9000 FIVE-STAR REVIEWS
5% OFF ALL SUBSCRIPTIONS
100% HAPPINESS GUARANTEE
Analyze Diet
0
Home / Equine Research Bank / J Vet Intern Med / Incidence, recurrence, and outcome of postrace atrial fibril...
Journal of veterinary internal medicine2021; 35(2); 1111-1120; doi: 10.1111/jvim.16063

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

Abstract: Atrial fibrillation (AF) impacts performance and horse and jockey safety. Understanding the outcomes of AF identified postrace will better inform regulatory policy. Objective: 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. Methods: 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: 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.
© 2021 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC. on behalf of the American College of Veterinary Internal Medicine.
Get Full Text
Publication Date: 2021-02-19 PubMed ID: 33604980PubMed Central: PMC7995445DOI: 10.1111/jvim.16063Google Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
LinkedInCopy
  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The article discusses a research study into the incidence, recurrence, and impact of atrial fibrillation, which is a type of heart condition, in Thoroughbred racehorses. The results reveal an increased risk of repeat atrial fibrillation in horses that have previously experienced an episode, and this is found to impact performance and overall safety.

Methodology

  • The researchers collected data from the race records of 4684 Thoroughbred racehorses that competed in Hong Kong races between 2007 and 2017.
  • Horses that underperformed were subjected to a heart exam, including a cardiac auscultation and Electrocardiography (ECG).
  • Incidence and recurrence of atrial fibrillation (AF) among these horses were then investigated, with careful comparison made between horses with and without a history of the disease, and between those with short-term and long-term episodes.
  • The Fisher’s exact test, a statistical tool used for small sample sizes, was employed to make these comparisons.

Findings

  • Out of 96,135 racing starts in the period under review, AF was identified in 4.9% of the horses, at an overall rate of 2.7 episodes per 1000 starts.
  • Horses with prior records of AF had an incidence rate five times higher than those without such history, with proportions of 12.8 versus 2.4 episodes per 1000 starts, respectively.
  • Among horses that had been treated for long-term AF, 64% experienced recurrence, a number significantly higher than the 23% recurrence noted in horses with short-term AF.
  • The median time between episodes was 343 days, though the range was broad – from just over a month to nearly three years.

Conclusion

  • Thoroughbred racehorses that have experienced either short-term or persistent episodes of AF are at a heightened risk of a recurrence, but the interim periods can vary greatly.
  • This reveals a considerable burden of AF among these horses, which has implications for their competitive performance and overall wellbeing.

Cite This Article

APA
Nath LC, Elliott AD, Weir J, Curl P, Rosanowski SM, Franklin S. (2021). Incidence, recurrence, and outcome of postrace atrial fibrillation in Thoroughbred horses. J Vet Intern Med, 35(2), 1111-1120. https://doi.org/10.1111/jvim.16063

Publication

Journal of veterinary internal medicine
ISSN: 1939-1676
NlmUniqueID: 8708660
Country: United States
Language: English
Volume: 35
Issue: 2
Pages: 1111-1120

Researcher Affiliations

Nath, Laura C
  • School of Animal & Veterinary Sciences, University of Adelaide, Roseworthy, South Australia, Australia.
Elliott, Adrian D
  • Centre for Heart Rhythm Disorders, Adelaide Medical School, University of Adelaide, Adelaide, South Australia, Australia.
Weir, Joe
  • Hong Kong Jockey Club, Veterinary Clinical Services, Equine Hospital, Hong Kong SAR, Hong Kong.
Curl, Peter
  • Veterinary Regulation, Hong Kong Jockey Club, Hong Kong SAR, Hong Kong.
Rosanowski, Sarah M
  • EVC Global LTD, Hong Kong, Hong Kong.
Franklin, Samantha
  • School of Animal & Veterinary Sciences, University of Adelaide, Roseworthy, South Australia, Australia.

MeSH Terms

  • Animals
  • Atrial Fibrillation / epidemiology
  • Atrial Fibrillation / veterinary
  • Hong Kong
  • Horse Diseases / epidemiology
  • Horses
  • Incidence
  • Odds Ratio
  • Recurrence

Grant Funding

  • Agrifutures Australia
  • Racing Victoria

Conflict of Interest Statement

Authors declare no conflict of interest.

References

This article includes 67 references
  1. Hitchens PL, Hill AE, Stover SM. The role of catastrophic injury or sudden death of the horse in race‐day jockey falls and injuries in California, 2007‐2012.. Equine Vet J 2014;48(1):50–56.
    pubmed: 25417895
  2. Deem D, Fregin G. Atrial fibrillation in horses: a review of 106 clinical cases, with consideration of prevalence, clinical signs, and prognosis.. J Am Vet Med Assoc 1982;180:261‐265.
    pubmed: 7056674
  3. Kiryu K, Machida N, Kashida Y, Yoshihara T, Amada A, Yamamoto T. Pathologic and electrocardiographic findings in sudden cardiac death in racehorses.. J Vet Med Sci 1999;61:921‐928.
    pubmed: 10487232
  4. Reef VB, Bonagura J, Buhl R. Recommendations for management of equine athletes with cardiovascular abnormalities.. J Vet Intern Med 2014;28:749‐761.
    pmc: PMC4895474pubmed: 24628586
  5. Allen K, Young L, Franklin S. Evaluation of heart rate and rhythm during exercise.. Equine Vet Educ 2016;28:99‐112.
  6. Martin BB Jr, Reef VB, Parente EJ, Sage AD. Causes of poor performance of horses during training, racing, or showing: 348 cases (1992‐1996).. J Am Vet Med Assoc 2000;216:554‐558.
    pubmed: 10687012
  7. Jose‐Cunilleras E, Young LE, Newton JR, Marlin DJ. Cardiac arrhythmias during and after treadmill exercise in poorly performing thoroughbred racehorses.. Equine Vet J Suppl 2006;38:163‐170.
    pubmed: 17402413
  8. Ryan N, Marr CM, McGladdery AJ. Survey of cardiac arrhythmias during submaximal and maximal exercise in thoroughbred racehorses.. Equine Vet J 2005;37:265‐268.
    pubmed: 15892238
  9. Physick‐Sheard PW, McGurrin MK. Ventricular arrhythmias during race recovery in Standardbred Racehorses and associations with autonomic activity.. J Vet Intern Med 2010;24:1158‐1166.
    pubmed: 20584140
  10. Slack J, Boston RC, Soma LR, Reef VB. Occurrence of cardiac arrhythmias in Standardbred racehorses.. Equine Vet J 2015;47:398‐404.
    pubmed: 24819401
  11. Holmes JR. Cardiac arrhythmias on the racecourse.. Equine Exerc Physiol 1987;2:781‐785.
  12. Ohmura H, Hiraga A, Takahashi T, Kai M, Jones JH. Risk factors for atrial fibrillation during racing in slow‐finishing horses.. J Am Vet Med Assoc 2003;223:84‐88.
    pubmed: 12839069
  13. Williams R, Harkins L, Hammond C, Wood J. Racehorse injuries, clinical problems and fatalities recorded on British racecourses from flat racing and National Hunt racing during 1996, 1997 and 1998.. Equine Vet J 2001;33:478‐486.
    pubmed: 11558743
  14. Holmes JR, Henigan M, Williams RB, Witherington DH. Paroxysmal atrial fibrillation in racehorses.. Equine Vet J 1986;18:37‐42.
    pubmed: 3948829
  15. Nath L, Anderson G, Hinchcliff K, Savage C. Serum cardiac troponin I concentrations in horses with cardiac disease.. Aust Vet J 2012;90:351‐357.
    pubmed: 22928683
  16. McGurrin M, Physick‐Sheard P, Kenney D. Transvenous electrical cardioversion of equine atrial fibrillation: patient factors and clinical results in 72 treatment episodes.. J Vet Intern Med 2008;22:609‐615.
    pubmed: 18466256
  17. Vernemmen I, De Clercq D, Decloedt A, Vera L, Van Steenkiste G, van Loon G. Atrial premature depolarisations five days post electrical cardioversion are related to atrial fibrillation recurrence risk in horses.. Equine Vet J 2020;52:374‐378.
    pubmed: 31583742
  18. Linz D, Hesselkilde E, Kutieleh R, Jespersen T, Buhl R, Sanders P. Pulmonary vein firing initiating atrial fibrillation in the horse: oversized dimensions but similar mechanisms.. J Cardiovasc Electrophysiol 2020;31:1211‐1212.
    pubmed: 32108401
  19. Verheyen T, Decloedt A, van der Vekens N, Sys S, De Clercq D, van Loon G. Ventricular response during lungeing exercise in horses with lone atrial fibrillation.. Equine Vet J 2013;45:309‐314.
    pubmed: 23094848
  20. Benito B, Gay‐Jordi G, Serrano‐Mollar A. Cardiac arrhythmogenic remodeling in a rat model of long‐term intensive exercise training.. Circulation 2011;123:13‐22.
    pubmed: 21173356
  21. Guasch E, Benito B, Qi X. Atrial fibrillation promotion by endurance exercise: demonstration and mechanistic exploration in an animal model.. J Am Coll Cardiol 2013;62:68‐77.
    pubmed: 23583240
  22. Aschar‐Sobbi R, Izaddoustdar F, Korogyi AS. Increased atrial arrhythmia susceptibility induced by intense endurance exercise in mice requires TNFα.. Nat Commun 2015;6:6018.
    pmc: PMC4661059pubmed: 25598495
  23. La Gerche A, Heidbuchel H. Can intensive exercise harm the heart? You can get too much of a good thing.. Circulation 2014;130:992‐1002.
    pubmed: 25223770
  24. Elliott AD, Linz D, Verdicchio CV, Sanders P. Exercise and atrial fibrillation: prevention or causation?. Heart Lung Circ 2018;27:1078‐1085.
    pubmed: 29891251
  25. Maron BJ, Pelliccia A. The heart of trained athletes: cardiac remodeling and the risks of sports, including sudden death.. Circulation 2006;114:1633‐1644.
    pubmed: 17030703
  26. Reef VB, Levitan CW, Spencer PA. Factors affecting prognosis and conversion in equine atrial fibrillation.. J Vet Intern Med 1988;2:1‐6.
    pubmed: 3221350
  27. Decloedt A, Schwarzwald CC, De Clercq D. Risk factors for recurrence of atrial fibrillation in horses after cardioversion to sinus rhythm.. J Vet Intern Med 2015;29:946‐953.
    pmc: PMC4895430pubmed: 25917409
  28. De Clercq D, Decloedt A, Sys SU, Verheyen T, Van Der Vekens N, van Loon G. Atrial fibrillation cycle length and atrial size in horses with and without recurrence of atrial fibrillation after electrical cardioversion.. J Vet Intern Med 2014;28:624‐629.
    pmc: PMC4858013pubmed: 24611990
  29. Decloedt A, de Clercq D, van der Vekens N, Verheyen T, van Loon G. Noninvasive determination of atrial fibrillation cycle length by atrial colour tissue Doppler imaging in horses.. Equine Vet J 2014;46:174‐179.
    pubmed: 23738919
  30. Decloedt A, Verheyen T, Van Der Vekens N, Sys S, De Clercq D, van Loon G. Long‐term follow‐up of atrial function after cardioversion of atrial fibrillation in horses.. Vet J 2013;197:583‐588.
    pubmed: 23823082
  31. De Clercq D, Van Loon G, Tavernier R, Duchateau L, Deprez P. Atrial and ventricular electrical and contractile remodeling and reverse remodeling owing to short‐term pacing‐induced atrial fibrillation in horses.. J Vet Intern Med 2008;22:1353‐1359.
    pubmed: 19000247
  32. Hesselkilde EZ, Carstensen H, Haugaard MM. Effect of flecainide on atrial fibrillatory rate in a large animal model with induced atrial fibrillation.. BMC Cardiovasc Disord 2017;17:289.
    pmc: PMC5723027pubmed: 29221440
  33. Club HKJ. Department of veterinary regulation welfare and biosecurity policy.. Hong Kong Jockey Club 2019;54.
  34. de Solis CN. Ventricular arrhythmias in horses: diagnosis, prognosis and treatment.. Vet J 2020;261:105476.
    pubmed: 32741491
  35. nHong Kong Jockey Club racing index; 2020. https://racing.hkjc.com/racing/english/index.aspxn
  36. Kim H‐Y. Statistical notes for clinical researchers: chi‐squared test and Fisher's exact test.. Restor Dent Endod 2017;42:152‐155.
    pmc: PMC5426219pubmed: 28503482
  37. Naylor JM, Yademuk LM, Pharr JW, Ashbumer JS. An assessment of the ability of diplomates, practitioners, and students to describe and interpret recordings of heart murmurs and arrhythmia.. J Vet Intern Med 2001;15:507‐515.
    pubmed: 11817055
  38. Chen S‐A, Hsieh M‐H, Tai C‐T. Initiation of atrial fibrillation by ectopic beats originating from the pulmonary veins: electrophysiological characteristics, pharmacological responses, and effects of radiofrequency ablation.. Circulation 1999;100:1879‐1886.
    pubmed: 10545432
  39. Schwarzwald CC, Schober KE, Bonagura JD. Echocardiographic evidence of left atrial mechanical dysfunction after conversion of atrial fibrillation to sinus rhythm in 5 horses.. J Vet Intern Med 2007;21:820‐827.
    pubmed: 17708405
  40. van Loon G. Atrial Pacing and Experimental Atrial Fibrillation in Equines Faculty of Veterinary Medicine.. Merelbeke, Belgium: Ghent University; 2001.
  41. De Vos CB, Pisters R, Nieuwlaat R. Progression from paroxysmal to persistent atrial fibrillation: clinical correlates and prognosis.. J Am Coll Cardiol 2010;55:725‐731.
    pubmed: 20170808
  42. Young LE. Cardiac responses to training in 2 year old thoroughbreds: an echocardiographic study.. Equine Vet J 1999;31:195‐198.
    pubmed: 10659251
  43. Young LE, Wood JL. Effect of age and training on murmurs of atrioventricular valvular regurgitation in young thoroughbreds.. Equine Vet J 2000;32:195‐199.
    pubmed: 10836473
  44. Sanchis‐Gomar F, Perez‐Quilis C, Lippi G. Atrial fibrillation in highly trained endurance athletes—description of a syndrome.. Int J Cardiol 2017;226:11‐20.
    pubmed: 27776250
  45. Else RW, Holmes JR. Cardiac pathology in the horse. 2. Microscopic pathology.. Equine Vet J 1972;4:57‐62.
    pubmed: 4666289
  46. Boden LA, Charles JA, Slocombe RF. Sudden death in racing Thoroughbreds in Victoria, Australia.. Equine Vet J 2005;37:269‐271.
    pubmed: 15892239
  47. Lyle CH, Uzal FA, McGorum BC. Sudden death in racing Thoroughbred horses: an international multicentre study of post mortem findings.. Equine Vet J 2011;43:324‐331.
    pubmed: 21492210
  48. DeLay J. Postmortem findings in Ontario racehorses, 2003‐2015.. J Vet Diagn Investig 2017;29:457‐464.
    pubmed: 28382856
  49. Molesan A, Wang M, Sun Q. Cardiac pathology and genomics of sudden death in racehorses from New York and Maryland racetracks.. Vet Pathol 2019;56(4):575–585.
    pubmed: 30917748
  50. Frost L, Overvad K, Tjønneland A, Fenger‐Grøn M. Lean body mass is the predominant anthropometric risk factor for atrial fibrillation.. J Am Coll Cardiol 2016;69:2488‐2497.
    pubmed: 28521886
  51. Physick‐Sheard P, Kraus M, Basrur P, McGurrin K, Kenney D, Schenkel F. Breed predisposition and heritability of atrial fibrillation in the Standardbred horse: a retrospective case–control study.. J Vet Cardiol 2014;16:173‐184.
    pubmed: 25087649
  52. Leroux A, Detilleux J, Sandersen C. Prevalence and risk factors for cardiac diseases in a hospital‐based population of 3,434 horses (1994–2011).. J Vet Intern Med 2013;27:1563‐1570.
    pubmed: 0
  53. Kraus M, Physick‐Sheard P, Brito LF, Sargolzaei M, Schenkel FS. Marginal ancestral contributions to atrial fibrillation in the Standardbred racehorse: comparison of cases and controls.. PLoS One 2018;13:e0197137.
    pmc: PMC5953485pubmed: 29763439
  54. Kraus M, Physick‐Sheard P, Brito L, Schenkel F. Estimates of heritability of atrial fibrillation in the Standardbred racehorse.. Equine Vet J 2017;49:718‐722.
    pubmed: 28391631
  55. McGurrin MKJ, Physick‐Sheard PW, Kenney DG. Transvenous electrical cardioversion of equine atrial fibrillation: patient factors and clinical results in 72 treatment.. J Vet Intern Med 2008;22:609‐615.
    pubmed: 18466256
  56. Rosanowski S, Chang Y, Stirk A, Verheyen K. Descriptive epidemiology of veterinary events in flat racing thoroughbreds in Great Britain (2000 to 2013).. Equine Vet J 2017;49:275‐281.
    pubmed: 27208544
  57. Heliczer N, Mitchell K, Lorello O. Atrial fibrillation management in a breeding stallion.. J Vet Cardiol 2017;19:299‐307.
    pubmed: 28336184
  58. Buhl R, Carstensen H, Hesselkilde EZ. Effect of induced chronic atrial fibrillation on exercise performance in Standardbred trotters.. J Vet Intern Med 2018;32:1410‐1419.
    pmc: PMC6060327pubmed: 29749082
  59. Broux B, De Clercq D, Decloedt A. Atrial premature depolarization‐induced changes in QRS and T wave morphology on resting electrocardiograms in horses.. J Vet Intern Med 2016;30:1253‐1259.
    pmc: PMC5089572pubmed: 27209267
  60. Reef V, Davidson E, Slack J, Stefanovski D. Hypercapnia and hyperlactatemia were positively associated with higher‐grade arrhythmias during peak exercise in horses during poor performance evaluation on a high‐speed treadmill.. Vet J 2020;266:105572.
    pubmed: 33323171
  61. Slack J, Stefanovski D, Madsen T, Fjordbakk C, Strand E, Fintl C. Cardiac arrhythmias in poorly performing Standardbred and Norwegian–Swedish Coldblooded trotters undergoing high‐speed treadmill testing.. Vet J 2020;267:105574.
    pubmed: 33375960
  62. Suyama AC, Sunagawa K, Sugimachi M, Anan T, Egashira K, Takeshita A. Differentiation between aberrant ventricular conduction and ventricular ectopy in atrial fibrillation using RR interval scattergram.. Circulation 1993;88:2307‐2314.
    pubmed: 7693363
  63. Zipes DP. Heart‐brain interactions in cardiac arrhythmias: role of the autonomic nervous system.. Cleve Clin J Med 2008;75:S94.
    pubmed: 18540155
  64. Chang S‐L, Tai C‐T, Lin Y‐J. Electrophysiological characteristics and catheter ablation in patients with paroxysmal supraventricular tachycardia and paroxysmal atrial fibrillation.. J Cardiovasc Electrophysiol 2008;19:367‐373.
    pubmed: 18179522
  65. Jesty SA, Kraus MS, Johnson AL, Gelzer AR, Bartol J. An accessory bypass tract masked by the presence of atrial fibrillation in a horse.. J Vet Cardiol 2011;13:79‐83.
    pubmed: 21324767
  66. Viu J, Armengou L, Decloedt A, Jose‐Cunilleras E. Investigation of ventricular pre‐excitation electrocardiographic pattern in two horses: clinical presentation and potential causes.. J Vet Cardiol 2018;20:213‐221.
    pubmed: 29573995
  67. nPPS import criteria; 2020. https://racing.hkjc.com/racing/english/racing-info/pps_import_critieria.aspn

Citations

This article has been cited 9 times.
  1. Natterson-Horowitz B, Wright K, Van Steenkiste G, Decloedt A, Gagnon AL, Cai X, Mazmanian A. Arrhythmias across the tree of life: comparative insights for human electrophysiology. Front Cardiovasc Med 2025;12:1652591.
    doi: 10.3389/fcvm.2025.1652591pubmed: 41567384google scholar: lookup
  2. Kapusniak A, Lara NM, Hitchens PL, Bailey S, Nath L, Franklin S. Use of Artificial Intelligence to Detect Cardiac Rhythm Disturbances in Athletes: A Scoping Review. J Vet Intern Med 2025 Nov-Dec;39(6):e70257.
    doi: 10.1111/jvim.70257pubmed: 41017277google scholar: lookup
  3. Nissen SD, Bastrup JA, Haugaard SL, Marion-Knudsen R, Schneider M, Kjeldsen ST, Carstensen H, Hopster-Iversen C, Nattel S, Jepps TA, Buhl R. Horse model of spontaneous atrial fibrillation share proteomic changes with humans. Sci Rep 2025 Aug 28;15(1):31694.
    doi: 10.1038/s41598-025-16885-7pubmed: 40877415google scholar: lookup
  4. Kjeldsen ST, Nissen SD, Christensen NC, Haugaard SL, Schneider MJ, Vinther Z, Sattler SM, Carstensen H, Jøns C, Hopster-Iversen C, Buhl R. Validation and clinical application of implantable loop recorders for diagnosis of atrial fibrillation in horses. Equine Vet J 2025 Mar;57(2):449-458.
    doi: 10.1111/evj.14112pubmed: 39031582google scholar: lookup
  5. Nath LC, Saljic A, Buhl R, Elliott A, La Gerche A, Ye C, Schmidt Royal H, Lundgren Virklund K, Agbaedeng TA, Stent A, Franklin S. Histological evaluation of cardiac remodelling in equine athletes. Sci Rep 2024 Jul 19;14(1):16709.
    doi: 10.1038/s41598-024-67621-6pubmed: 39030282google scholar: lookup
  6. Nath LC, Elliott A, La Gerche A, Weir J, Forbes G, Thomas G, Franklin S. Associations between postrace atrial fibrillation and measures of performance, racing history and airway disease in horses. J Vet Intern Med 2023 Nov-Dec;37(6):2573-2583.
    doi: 10.1111/jvim.16878pubmed: 37740606google scholar: lookup
  7. White R, Nath L, Hebart M, Franklin S. Assessment of P Wave Indices in Healthy Standardbred Horses. Animals (Basel) 2023 Mar 16;13(6).
    doi: 10.3390/ani13061070pubmed: 36978611google scholar: lookup
  8. Kjeldsen ST, Nissen SD, Buhl R, Hopster-Iversen C. Paroxysmal Atrial Fibrillation in Horses: Pathophysiology, Diagnostics and Clinical Aspects. Animals (Basel) 2022 Mar 10;12(6).
    doi: 10.3390/ani12060698pubmed: 35327097google scholar: lookup
  9. Ter Woort F, Dubois G, Tansley G, Didier M, Verdegaal L, Franklin S, Van Erck-Westergren E. Validation of an equine fitness tracker: ECG quality and arrhythmia detection. Equine Vet J 2022 Feb 9;55(2):336-43.
    doi: 10.1111/evj.13565pubmed: 35138653google scholar: lookup
Subscribe to our newsletter
Join 99,344 horse owners like you who receive our email updates on horse health and nutrition.