HSI vs SHI

Well, I haven’t blogged in a very long time. My inspiration for my blog stems from trail riding over here on the west side of mountains of Washington state.  I have lived on the Eastern side for many years, and thought nothing of riding my horse/mule up in the mountains with temperatures in the 90’s. 

I was surprised that although the temperatures here are milder than Eastern Washington, humidity plays a huge role. What can be considered as moderate exercise (3 hour conditioning ride-1 hour trotting /loping in an arena) can have the same effect as intense activity as heat and humidity rise. 

As responsible horse owners, you owe it to yourself to understand the H.S.I.  Ahh you ask, what does that stand for?  It stands for the Heat Stress Index, and you need to know how to figure this out.  This  is the formula for your HSI:

Take the sum of the temperature in degrees fahrenheit, plus the percent humidity and this gives you an H.S.I. number.  Easy peasy.  So the temperature today is 78 degrees Fahrenheit and the humidity is 39%. My HSI is 117.  I am good to go (see below) and ride with reckless abandon, except for the fact that I over did it yesterday trying to impersonate a mountain goat riding my mule at Mt. St Helens on the Cinnamon Trail.  This is where the SHI (Stupid Human Index) can often leave you riding with a high HSI number. 

Now, your probably thinking to yourself.  O.k., so I have a number now what?  As a general rule of thumb, if your H.S.I. number is <120, your “good to go.”

If the sum is >150 , especially if the humidity gives you more than half of this number, your horses ability to cool himself will be compromised.  So does this mean you can’t ride if the HSI  >150?  No, not necessarily, it means that you need to either lower the intensity or duration of workout , or ride later in the day.  If the HSI is >180 your horse cannot regulate his body temperature naturally and he should not be forced to work.

There are times when you have little to no choice to ride.  For example, you have an afternoon class at the show, or you are ascending 3000 feet in less than 2 hours and your HSI is now 158 (Not that I would have done something like this, lol)  So what do you do then?  Well, common sense should prevail, but at the very least you need to know the signs/symptoms of dehydration and take appropriate action.

My HSI was 158 for Daisy at the summit.  I took frequent short rest breaks, stood in the shade, and sponged her off in every stream we came to, as well as walked a significant portion of the ride. This prevented her from becoming stressed and dehydrated.  It didn't help me however, as my SHI was running particularly high yesterday.  This is a picture of the ascent through red rock pass.

Anyway, back to the topic of dehydration. Horses don’t just lose water when they sweat; they also lose minerals and salts aka electrolytes.  A horse that is mildly dehydrated will show little symptoms and can be remedied by drinking fresh water. 

The Signs

Skin pinch test:  Pinch an inch of skin on your horses neck in front of the shoulder and pull it towards you.  What happens when you let go?  If your horse is hydrated, it should snap back almost immediately.  If the skin tents and doesn’t snap back, he’s dehydrated.

Other things to look for: The horses stool will become harder and dry looking and the urine will become increasingly yellow and maybe even brown tinged;   your horse may become lethargic.

On an important note, I have heard people on the trail saying, “My horse is so fit, he hasn’t broken a sweat coming up that mountain.”  So, in the advanced stage of dehydration, a horse may quit sweating completely in order to conserve fluids. 

How to Cool Your Horse Effectively:

Move your horse to a shaded area and hose the entire body with cold water.  There has been much discussion on whether this might cause muscle cramping, i.e. tying up.  In a study done previous to the 1996 Atlanta Olympics, it was concluded by Jonathan Forman, DVM University of Illinois, “That if you put nearly freezing water in large volumes all over the muscles of the horse, you can draw a lot of heat out of the muscles and the horse will not tie up afterwards.”  So go ahead and put that ice-cold water on him!  If after 30 minutes your horses pulse does not drop below 64bpm the condition is serious and you should call a vet.  Please remember that I am not a veterinarian and my advice only comes from research articles and experience.  You should always consult with your veterinarian if you think your horse is in trouble. 

  

Useful tips for trail riding.  Most endurance riders carry a sponge either clipped to the saddle or, like me, with a long string attached so you can dip the sponge in the water when crossing creeks and sponge the water over the horses neck.  I have seen others carry a scoop made from milk jugs, so they can scoop up water when they are unable to get their horse down to the creek. Action rider has a great selection of trail riding gear and accessories for those interested. I also like Moss Rock Endurance, Mad Tack, Running Bear and Hought.

Well, I hope you have learned a little about HSI, and if you already knew this, as I know many of you do, then kudos to you for being well informed. Please share this information with others.  I have had horses my entire life, and didn’t learn this until 2 years ago.  It’s not rocket science, but it is very useful and might prevent tying up, colic and heat exhaustion on the trail.  I hope to gather information and blog on Electrolytes, human trail riding comfort items and beginning training on my yearling foxtrotter next.   I will keep everyone updated.

Now get on out there and enjoy the Ray’s!  Cheers!

Squirrel.