Written by: Kim French

How climate change is affecting horse health around the world.

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While there is plenty of debate in scientific circles as to whether climate change is the result of human activity or just part of the ongoing natural cycle of warming and cooling of the Earth, there is little doubt that our terrestrial climate is changing.

With average temperatures rising almost two degrees Fahrenheit since the early twentieth century, and an increase of atmospheric carbon dioxide and methane levels, our planet’s climate is trending warmer. This evolution becoming a cause for concern for horse breeders and owners looking ahead over the next few decades.

Challenge of Heat and Cold

All living organisms must adapt to their environment, and horses are no different. The two biggest threats to breeding and keeping horses healthy and well-cared-for in the face of climate change shifting towards warmer global temperatures are the increase of susceptibility to infectious disease and complications of reproduction due to environmental factors.

With temperatures trending higher, seasonal climate patterns include summers that are hotter, winters that are actually colder, an increase in severity of storms which can cause floods, tornadoes and hurricanes and inversely, longer periods of droughts in certain geographic locations.

Horses can become overheated or suffer heat exhaustion-related illnesses during times of very warm temperatures. The need for more water and shade becomes evident in hot summer months, and the availability of good-quality fresh forage may be compromised in times of drought.

The colder winters associated with this type of climate change necessitate adequate shelter for longer periods of time, which negates any natural foraging and renders a horse’s diet completely dependent on human provision. A high-calorie, high-fibre diet in cold months is crucial to keep an adequate body temperature.

More severe storms can bring massive floods, and with it water-related problems, from life-threatening river surges to muddy pastures that can cause hoof problems and the presence of insects which can be carriers of infectious disease.

A Hotbed of Disease

In a 2006 presentation at the 17th International Conference of Racing Analysts and Veterinarians held in Antalya, Turkey, noted microbiologist Gary Muscatello, PhD, BVSc, of the University of Sydney Faculty of Veterinary Science stated, “The general principles of a warmer environment and changing weather patterns influence many factors, which encourage disease outbreaks, disease transmission, and the emergence of new diseases.”

Muscatello went further to state that “the disease-causing pathogens themselves replicate at a higher rate, and subsequently can potentially generate more virulent, novel strains,” which would in turn cause newer disease outbreaks.

In a 2009 Cambridge University study by Dr. Paul Gale et al., climate change was “predicted to increase the risk of incursion from entry of vectors for … viruses to some degree, the strongest effects being predicted for African Horse Sickness Virus (AHSV), Crimean-Congo Hemorrhagic Fever Virus (CCHFV), and West Nile Virus (WNV).”

African Horse Sickness virus causes circulatory and respiratory lesions, and is insect-borne. Culicoides midges, a type of fly, carry and can transmit AHSV by biting horses. They have also been known to transmit Bluetongue virus, another potential disease endemic for the horse population of sub-Saharan Africa.

Mortality rates of AHSV can be as high as 90% depending on the strain, and full recovery from acute illness caused by the virus is rare. Laboratory testing is the only sure method of diagnosing AHSV, but respiratory symptoms include cardiovascular edema, interlobular edema, spasmodic coughing, and fever. There is, however, a vaccine for the disease.

Crimean-Congo Hemorrhagic Fever Virus is a tick-borne virus most notably found in eastern Europe, the Mediterranean region, central Asia, the Middle East, northern Africa and the Indian subcontinent. CCHFV is asymptomatic in the equine, but infected horses can act as an “amplifying host” and pass the stronger strain of virus to humans through tick bites, mainly from ticks of the genus Hyalomma. The fatality rate in humans infected with CCHFV can be as high as 40%.

West Nile Virus is endemic to North America. While infection must be clinically verified in the laboratory, equine symptoms include depression, ataxia, lameness, partial paralysis and other neurologic signs accompanying fever. Vaccination against WNV is the primary form of protection against the disease, but cases are still found at varying times of the year. In Ontario, two cases were reported in August of 2017. Most cases are detected in the months of August and September, but “cases can occur into October if environmental conditions permit the survival of the mosquito vector species.”

Drought Dangers

The challenges of these and other types of climate change-induced illnesses are many and complex. Bacterial infections, breakdowns of pasture lands, water contamination, and severe drought all pose threats to horses in a rapidly-changing climate.

Pigeon Fever, for instance, is on the rise. Rarely seen prior to 2009, in 2011 following a historic drought in Texas, there were 40-50 cases in the fall. The corynebacterium, which lives in the soil, seems to rear its head once it rains after a prolonged drought and manure provides a food source for the organism.

Also in Texas in the fall of 2011 was a much higher instance of salmonella in adult horses than is usual for that time of year, again following the first significant rain after months of drought. In this case it was unclear whether it was released in the soil or manure due to the rain, or arrived with all the hay being brought in from out-of-state during the drought.

Drought also seems to trigger an increase in rabies, a fatal neurological disease that is easily preventable with a regular vaccination. It is believed that the water shortage attracts wild animals who may be carriers to ponds and troughs in horses’ fields, thus exposing them.

Baby Blues

Reproduction issues may also arise in conjunction with climate change. Onset of seasonal ovulation has been proven to be affected by changes in temperatures. A 10-year study concluded in 1994 by M.V. Guerin and X.J. Wang analyzed the time of onset of seasonal ovulation in mares and found a “significant variation” between years. They surmised that “environmental temperature may therefore play an important adjuvant zeitgeber [a cue given by the environment to reset the internal body clock] for the timing of the first ovulation of estrus in the mare.” Guerin and Wang also showed a “significant negative correlation between the mean weekly temperatures and the time of ovulation.”

Muscatello and fellow researcher Peter Knight found that “reduced rainfall may decrease pasture growth with resulting adverse effects on breeding activities.” Their study supported the findings of E.M. Carnevale in 1997 that “mares grazing pasture have been shown to begin ovulating sooner than those being fed hay.”

The ramifications of high temperatures ruining pasture land become abundantly clear: if there isn’t enough rain to support the pasture, and mares are hay-fed for long periods, their ovulation cycles will be delayed. When taking into consideration rigid breeding seasons for race horses, those dates may become compromised as mares will become fertile later than normal.

Maintaining vigilant animal husbandry in efforts to stay ahead of any possible complications brought upon by climate change is the best course of action. Water conservation while providing ample amounts of clean water is a must. Pasture management through rotation, reseeding, and having a ‘sacrifice’ paddock during rainy weather becomes even more important to maintain healthy plant growth and longevity. Manure management should remain a priority to help prevent a myriad of possible disease processes. Immunizations should be kept up to date, and regular veterinary check-ups should be afforded.

Understanding how current and future climate shifts can affect the health and safety of your horses will ensure you are prepared to keep them comfortable and secure in the ‘new normal’ of weather conditions.