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Critical Temperature – Preparing Your Horse for Cold Weather

By Justin High, DVM

Right now I am sitting at my computer writing this, and it’s 72 degrees and 83 percent humidity. In less than 24 hours, the temperature is set to drop to 35 degrees with rain and 17 mph winds! I love Texas, but I love it more in the summertime. So, when it comes to preparing our horses for weather like this, we need to plan ahead, just as you would with your stall water, or pipes. 

First off, God made horses with an amazing capacity to stay warm just as they are. For those of you wondering, they can even survive without blankets! Slick-haired show horses require blankets in layers, but since we have modified their hair coats, they are the exception, and not the rule. Keeping your horse warm and healthy in the extreme conditions is fairly simple. Obviously, feed and water are necessities when it’s hot or cold, but when the temperatures plunge, they are the even more critical.

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The key factor to this discussion is what’s called the critical temperature. It varies regionally and is the temperature at which horses require significant increases in digestible energy to maintain internal body temperature. All horses have a set amount of calories they need for maintenance of the basic body functions.  Exercise increases those demands accordingly, just as drops in the outside air temperature below the critical mark. For us in the North/Central Texas area, this critical temp is 45 degrees. 

For each 1 degree F drop below the critical temperature, a horse will require a 1 percent increase in digestible energy. Hair coat, humidity/moisture, and wind chill will also change the demands on digestible energy. For a horse with a wet hair coat, the critical temperature will increase by 10 to 15 degrees. Meaning, a dry horse at 45 degrees will need the same energy in feed as a wet horse in 55-60 degree weather.

I went to vet school for a reason – I’m bad at math. So, I need a simple method to figure changes in feeding rates. 

Say it’s 30 degrees with a wind chill of 25 degrees and no rain. (Always use the actual temp, not just the reported temp)

The average 1000-1100 pound horse requires 16.4 Mcal of digestible energy a day.

Current weather:   45 degrees – 25 degrees= 20 or a 20 percent increase in digestible energy.

So, 16.4Mcal (standard) x 20 percent=3.28Mcal increase demand due to temp change or 19.68Mcal total digestible energy demand.

Horses eat about 2 percent of their body weight a day and to use good, easy numbers the average pound of feed (hay and grain) has about 1Mcal of digestible energy. So, to figure our needed increase in feed we would:

1000 pound horse x 2 percent = 20 pounds of feed with a 3.28Mcal increase demand

1 pound of feed basically equals 1Mcal, so add another 3.25 pounds of feed per day for this horse under these conditions.

Easily, the best way to maintain a warm horse is to increase the hay content in its ration. Notice I did not say put out a round bale! The heat of combustion/digestion is a great way to increase the core temp of a cold horse and meet the increase nutritional demands the weather has placed on our horse. You cannot blanket a bad diet and expect good results.

Long story made short – water intake will make or break you in the winter time. I treat far more colics in the winter than in the summer strictly from horses not drinking enough and developing large and small colon impactions. Normally, a horse will drink about 1 gallon of water per 100 pounds of bodyweight without any other stressors included. Water consumption will decrease as water temperature falls. Without salt supplementation, water intake can drop to just several gallons per day as it approaches the freezing point. Simply adding a teaspoon of stock salt, or even better a mixture of regular salt (NaCl) and Lite salt (KCl), will dramatically increase water consumption even with freezing temperatures. Horse are like us. No one likes to drink cold water when you’re already that way. 

The time to prepare for cold weather is well before it makes its arrival. The colics usually don’t show up until a few days later when the increased feed has outweighed the decreased water intake, and now become an impaction that may require immediate attention. By keeping our horses warm with appropriate increases in their diets, adding salts, and monitoring their water intake we can all get through it.  Maybe not like it – but sure get through it. 

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Dr. Justin High is a veterinarian and partner in Reata Equine Hospital in Weatherford, Texas. He graduated vet school from Texas A&M University and completed an internship at The Littleton Equine Medical Center in Denver, Colo. High’s years of practice focuses on the Western performances horse. Send any comments or questions to justinhighdvm@reataequinehospital.com.