(Originally posted July 2012)

      This post is being written 30,000ft in the air as I head from Indy to NYC for a weekend full of a little bit of work and a lot of fun with friends and family. And I have to say, I’m pretty glad to be getting out of the Midwest. Today’s highs in Indianapolis are predicted to be 102F and that’s not counting the humidity! It was already 80 when we left home for the airport at 4:30AM and by 5:15 they had giant fans trying to cool passengers in line at security. While the East Coast is set to be a bit cooler over the next few days, these record highs at home has me worried about our equine friends, most of whom do not have A/C in their stalls.
I’m not the only one concerned. Officials at Churchill Downs in Louisville, KY cancelled racing for both yesterday and today, citing extreme temperatures and humidity. I spoke with the track veterinarian at my local track, Hoosier Park last night (where it was only in the 80s at race time) and while they are most likely going to continue the meet (the humidity is low and 20 mph breezes are predicted) they will have hoses placed all along the paddock and track-side as well as tubs of ice water to help cool horses before and after races.

     So how do these high temperatures and humidity levels affect our horses? Most of the research has been done on exercising horses and has universally shown that horses exercising in both high temps and high humidity have higher core body and blood temperatures, higher heart and respiratory rates, lower cardiac output, worse sweat response, longer recovery and a decreased ability to dissipate heat from their bodies. And while the horses in these studies were being run on treadmills at increased ambient temps you can imagine that even a horse just standing in a sun baked field would experience the same changes.     While we can’t bring our horses into our homes to enjoy the cool refreshment of central air (or even a window unit), we can take some simple steps to keep our horses cool and prevent heat stress.

1)    Shade- Temperatures in direct sunlight are going to be much higher than in the shade, so make sure your horses have the option to get out of the sun. Run in sheds, large trees or even keeping them in the barn can help keep them cool.

2)    Water- In high temperatures, and even more so in high humidity, more water is lost through sweat and increased respiration. Horses should always have access to fresh water but it’s even more important in this weather. So make sure your water troughs and buckets are full (and clean) at all times. If you’re not able to make it to the barn to refill them throughout the day, think about adding extra buckets to your stalls or paddocks.

3)    Electrolytes- Offering a salt or mineral block, placing an E-lyte powder on their feed or administering an electrolyte paste will not only replace important electrolytes lost through sweat but can also increase your horses’ drive to drink plenty of the aforementioned water.

4)    Baths- Cold hosing a horse and allowing them to air dry can help lower body temperature. The cold water will feel great and their wet hair will cool the skin through evaporation. For extreme conditions, water can be mixed 50/50 with rubbing alcohol to increase the evaporative effects. ** but make sure never to get any alcohol mix anywhere near your horses eyes!!**

5)    Ventilation- We all know how good a cool breeze feels. Placing fans in your barn aisles and in front of stalls can help keep things cool. Make sure barn doors and windows are open to let the air flow.

6)    Rest- Though we spend all winter dreaming of the days when we can ride across the fields, basking in the sunshine, extreme temperatures may be a good excuse to catch up on your favorite summer TV and give your horse a break. We discussed earlier that horses exercised in heat and humidity have much higher stress markers and much slower recovery. If you don’t have to train, don’t risk it. If you are getting ready for a big event, or use your horse in your work, plan activities early in the morning or in the evening when the temperatures are cooler.

7)    Protection from the Elements- The hot weather is caused by the sun’s rays, which also causes sunburns. Make sure to apply sunscreen to white noses which can become burnt just as easy as I turn into a lobster at the mere mention of UV rays! Warm weather also brings along biting insects which irritate and agitate your horses. Use fly sprays, fly masks and sheets to help keep your horse comfortable and bug-free.

Hopefully with these measures we can prevent the ill effects of heat stress. But how do you know if your horse is too hot? Signs of heat stress can include prolonged increased heart rate >60bpm and increased respiratory rate >80bpm (horses use deep breaths to try to blow off some of the steam, much like dogs panting, which helps cool blood flow to the brain). Hot horses should sweat as a natural cooling response but excessive sweat (especially in an inactive horse) should be a sign of excessive heat, and horses that stop sweating, despite other signs of overheating should be tending to immediately. Some horses will become agitated and display signs of colic as heat stress mounts. Rectal temperature gives you an estimate of core body temp and horses that reach 103F without having been recently exercised should be treated.

     Treatments include many of the same steps as prevention. Obviously you should immediately stop whatever activity you are doing and get the overheated horse out of the sun, under a hose and in front of a fan. Offer fresh water. Extreme cases, or cases that do not respond to the above measures should be seen by a veterinarian immediately. Prolonged high body temperatures can lead to systemic inflammation, denaturation of proteins and even multi-organ failure. You veterinarian can help lower your horses core temp by lavaging the stomach with cool water (via nasogastric tube) and administering cool fluids intravenously.  Bute or Banamine can also be administered, not necessarily to lower the body temperature but to prevent some of the ill effect of the inflammation induced by excessive heat.

    While every horse is at risk for heat stress, there are some that should be given special considerations. Older horses suffering from Cushing’s Disease will not shed out their winter coats. This extra fuzz traps heat in and prevents cooling. These horses should be body clipped to help them keep cool (don’t worry, clipping the hair now won’t affect its ability to grow back once the weather turns cooler). Horses with known respiratory problems such as Inflammatory Airway Disease or Heaves should also be monitored closely. Hot dry conditions can exacerbate their airway disease and decreased air exchange may contribute to higher body temps. Finally, foals who are being treated with a macrolide antimicrobial (erythromycin, azithromycin or clarithromycin) for Rhodococcus pneumonia should be kept in out of the sun. There have been reports of idiosyncratic hyperthermia in foals on erythromycin (though we should be cautious with all three) and drug induced heat combined with high ambient temps is a recipe for heat stroke.

     So as the numbers on the thermostat continue to rise, take some simple precautions to help keep your horses cool and healthy and keep a close eye out for any signs of heat stress.

Don't forget the dogs!
Dogs can also develop heat stroke in these high temps. Make sure if they are outside they have plenty of shade and fresh water (and a kiddie pool can go a long way to cool them down). And NEVER leave a dog in a car in the summer, even with the windows rolled down the temperatures inside can be lethal!

The birds are chirping, daffodils are popping up all over our yard (despite the demolition done to the bulbs this fall courtesy of a runaway stump-grinder) and the sun is shinning! March 20, 2012 marks the first day of spring in the northern hemisphere. So to kick off the new season here is the first installment of a 3-part series of blog posts. While we may all be excited to get back in the saddle and out on the trail, there are a few horse health topics we can’t forget, the darker side of this influx of warm air… And speaking of warm air, I don’t think anyone can argue that its been a mild winter and at least here in Indiana we seem to be moving right onto summer without much of a transition. Forget “In like a lion.” More like “In like an iguana baking in the desert sun!”  Two weekends ago, I wore long-johns to practice and could barely keep my fingers from turning blue. Last Saturday, it was 80 degrees at the kick-off of our first game. That kind of sudden heat really makes you re-evaluate your fitness level.

But what else does this sudden heat wave bring to life, besides the flowers and grass (and we’ll get to the evils of the spring grass next week)? Bugs! With no more overnight frosts, mosquito season is upon us, and much earlier than normal. Now I know what that means for me, coating myself in OFF and calamine lotion and being driven to insanity by hundreds of itchy bites. But it also has implications for our horses and their mental well-being. Mosquitoes can carry a group of viruses that cause encephalitis, or infection in the brain. These viruses include West Nile Virus (WNV), Eastern Equine Encephalitis (EEE, often called Triple-E) and Western Equine Encephalitis (WEE). There is also a Venezuelan Equine Encephalitis (VEE) but that hasn’t been seen in this country since the 1970s, though some people in southern Texas and Florida consider it a threat.

Life Cycle of the Viruses:
The virus has a life cycle that mainly involves wild birds. Remember it was a veterinarian who discovered West Nile Virus in crows in New York City back in 1999. Mosquitoes pick up the virus when they feed on an infected bird and then transfer the virus to horses, or humans, when they bite them. These viruses cannot live outside of a host and do not survive in the environment for long and the virus does not exist in high enough levels in the horse’s blood stream to transmit to other mosquitoes, horses or humans. Therefore isolation of infected cases is not required.

Clinical Signs:
EEE, WEE and WNV all act very similarly in the horse. The virus replicates in lymph nodes and infects the neurons in the brain. Clinical signs can appear anywhere from 2-3 days to as long as 3 weeks after infection. Signs may include: fever, depression, loss of appetite or neurologic signs (incoordination, staggering, hyperexitable, head pressing, leaning on walls, low head carriage, drooping lips/tongue or recumbency). Some horses may have intense puritis, or itchiness. Many horses infected with West Nile Virus will display very fine fasciculations of the muzzle that are often only noticed by seeing their whiskers quiver.  The course of the disease is between 2 to 14 days and fatality rates range from 33% with WNV, to 50% with WEE and up to a staggering 90% with EEE. The only treatment is supportive care (IV fluids/nutrition, anti-inflammatories and corticosteroids).  Horses that are lucky enough to recover may have residual neurologic deficits.

Prevention: Prevention includes vaccination and mosquito control (removal of stagnant water sources and liberal use of fly-sprays). When given properly (three initial shots 4-6 weeks apart, followed by an annual booster) the vaccines have been shown to be close to 100% effective.  The American Association of Equine Practitioners recommends that the, “annual re-vaccination must be completed prior to vector season in the spring. In animals of high risk or with limited immunity, more frequent vaccination or appropriately timed vaccination is recommended in order to induce protective immunity during periods of likely exposure. In areas where mosquitoes are active year-round, many veterinarians elect to vaccinate horses at 6 month intervals to ensure uniform protection throughout the year, although this practice is not specifically recommended by manufacturers of vaccines.”

So with the early onset of the warm weather, and hatching of billions upon billions of mosquito eggs, I would strongly recommend moving up your horse’s vaccination schedule to cover them against these devastating diseases as soon as you can. The bugs aren’t going to wait to bite your horse just because you’re not due for your spring shots till April! 

And don't forget about Fido and Fluffy! While dogs and cats rarely get these viral encephalidities, mosquitoes carry heartworm disease and the warm weather will bring out other undesirable critters like fleas and ticks which carry a whole set of diseases of their own like tape worms and Lyme Disease. So, if you take a break from your flea/tick/heartworm prevention in the winter, now is the time to start back up again!!