The biggest thing we’re going to want to think about when we think about winter nutrition is calories. Temperature isn’t the only thing we need to think about - wet, snowy and windy conditions (so basically the normal Canadian winters) all increase the horse’s calorie needs, especially when temperatures reach the horse’s lower critical temperature.
The lower critical temperature is the temperature at which metabolic heat production needs to be increased in order to maintain core body temp. During cold adaptation, metabolic rate rises and may become 2-3 times higher than normal maintenance level (Mejdell, Boe and Jorgensen, 2020). Wind and rain further impact the horse’s ability to thermoregulate, as wet or muddy hair can reduce the horse’s natural haircoat’s insulating qualities - a dry hair coat can tolerate more cold before requiring extra calories, sometimes differences as big as 7°C.
This is likely why horses have been reported to have a preference for wearing blankets when it’s rainy or windy (Mejdell et al, 2019), or using shelter during these conditions - in fact, a 20% improvement in heat conservation is reported when shelter is provided (Jorgensen, Mejdell and Boe, 2019; Cymbaluk, 1994).
There is no one specific lower critical temperature (LCT) for the equine species. LCT has a wide range depending on what the horse is adapted to, their body condition, hair coat, feeding, age and breed (Mejdell, Boe, and Jorgensen, 2020).So when we’re thinking about feeding and managing our horses for thermoregulation, we cannot just focus on LCT as a temperature, we need to consider factors that impact the horse’s normal thermoregulatory processes, such as wind chill or rain. In general, LCT can vary between 9°C to -15°C, depending on the situation. Regardless of the situation, when the temperatures are below that LCT, we’re going to want to add more calories to the diet.
What to feed?
When we’re thinking about how to add calories into the diet to support thermoregulation, forage is going to be your best bet. Not only is this the safest way, because your horse’s digestive tract is evolved to be eating foraging throughout the day, but the higher fiber content means that when hay is fermented in the hindgut, more heat is produced than would be when grain is digested in the small intestine.
We can be proactive about this by beginning to feed that extra hay 24 hours before the cold temperatures are expected - If you’re looking at the weather and you see that there’s going to be a big drop in temperature tomorrow night, let’s begin to feed that extra hay today.
If the nutritional value of your hay isn’t great or if you have a horse who cannot safely eat hay, you could incorporate soaked hay cubes or easily digestible beet pulp to your horse’s diet. As always, when adding a new feedstuff into your horse’s diet, you want to do so slowly and gradually, over a couple weeks, so really, feeding more hay is the easiest and safest way to meet increased calorie needs on a really cold day.
If there is sustained cold, then we have the room to gradually add a new feedstuff or tweak their base diet, but if your horse already has the stressor of extreme weather, don’t change their diet up that same day because their gut microbes are already going to be under stress. If you’re using a fat supplement to add more calories, you still have to be careful because horses do not have a gallbladder and require time to adjust to fat content in their diet.
Mindful Feeding Management
Even if we’re feeding extra hay during cold weather, we need to do so mindfully - frequent checks of your horse’s body condition is KEY during winter to ensure they are staying at a healthy weight.
For hard keepers, we want to take off that blanket and assess can we see ribs, if I put my hand on his back does it lay flat or is it more tented because he’s lost weight? This horse may need more calories!
For easy keepers, we want to take off that blanket and make sure we can still feel ribs, see if there’s a big jelly-like fat deposition behind the shoulder, does he have a crease in his back? We'll need to reduce calories in this horse's diet.
From there, we can adjust how suitable the diet is for that horse to make sure we don’t end up with other health issues, especially the easy keepers when spring grass starts to come into play.
Checking body condition at least every 2 weeks, but even weekly during extreme weather, is a great way to stay on top of this and manage your horse’s health proactively.
Did you change your horse's diet after your show season wrapped up? We want to make sure that we’re not cheating our horses of any essential nutrients during the winter - say you’re feeding 6 pounds of a fortified performance feed when you’re showing in the summer, but you cut it down to half that during the winter - this is going to put the horse at risk of not getting enough essential nutrients. Scaling calories when exercise is reduced is a great idea, but just make sure you’re not removing essential nutrients - this is where ration balancers or vitamin/mineral premixes are great for feeding less calories, but the same essential nutrients!
Hydration is CRITICAL!
While less obvious than in the summer months, we want to make sure our horses are staying hydrated. We want to ensure water intake increases as dry matter increases, so hydration is really important to making sure your horse’s digestive tract works properly. Make sure you have water available at all times, especially during turnout. There’s been research that barns that don’t provide water outside during in the winter have an increased risk of colic. Warmer water promotes more intake, so if possible, using a water heater or topping off your horse’s indoor water with some warm water can help encourage them to drink more.
Driving hydration by making sure you’re feeding salt (at least 20-30 grams), electrolytes can sometimes be useful for horses who don’t do a great job drinking, adding some water to their hard feeds.
Honos Hot Take: I don’t really recommend mashes because a lot of times, we’re introducing a feedstuff that your horse’s body isn’t used to, which adds another stressor on top of the cold. I’d rather horse owners just add water to your horse’s normal ration to avoid any digestive upset.
So, that was a lot of info…how much extra hay should I feed?
For a 500 kg horse, an easy to follow generalization is to increase calories by 2.5% per degree below the lower critical temperature (Cymbaluk, 1994), or feed an extra 0.15-0.17 kg hay per °C below the horse’s LCT (Morgan, 1995).
Generally, for the cold-adapted adult horse with a winter coat, the lower critical temp is -15°C, but young and old horses, or horses who are underweight, can be more sensitive to the cold.
So not to turn this into math class, but say you have an adult horse who is at a good weight, and it’s -20°C. This is 5° below their assumed lower critical temp, we’ll want to provide 5 x 2.5% more calories, so 12.5% more calories. An easy way to do that is to throw another kilogram of hay - flakes can range from 0.8 to 2.5 kg, so in a lot of cases, an extra flake might do the trick. Weighing your flakes is always recommended to get an idea of how much hay you’re feeding too!
We also have to remember that shelter and blanketing can play a role in calorie expenditure too!
Consider Blanketing: Nonblanketed horses will need more calories than blanketed horses - research has reported that at temperatures ranging from -3 to -12°C, nonblanketed horses eat 0.2% more hay per day, which is around an extra kilogram, or 2 Mcals (DeBoer et al, 2020), so making sure these horses especially have access to enough hay is really important.
Type of blanketing can impact calorie needs too, as different weights of blankets insulate more than others - for instance, thermographic imaging after cold exposure has shown that 200g and 400g blankets result in similar body surface temperatures, but significantly warmer than horses who were not blanketed or wearing a rainsheet (Hammer and Gunkleman, 2020).
So in this scenario, if your horse is wearing a blanket that doesn’t have insulation, you may need to feed more additional hay - again, there’s a TON of factors that impact how many additional calories your horse may need in cold weather.
Consider Shelter: If your horse’s coat is wet, calorie needs can even double! Studies have shown that horses can adapt to temperatures as low as -15*C, after 21 days (3 weeks), so supporting their caloric needs during extreme weather may not be how we’re going to feed them all winter.
Free-choice access to hay that is appropriate for the horse allows them the opportunity to adjust their feed intake accordingly (Mejdell, Boe and Jorgensen, 2020), which again speaks to how important it is to choose an appropriate forage for your horse - hay testing is a great tool for this.
For overweight horses, we don’t want to provide too many extra calories, but as the act of fiber digestion itself produces heat, using slow feed devices so the horse can eat hay all day, just slower, can help promote heat production and normal digestive function. Strategically managing their diet to allow maximal forage intake (ie, removing unnecessary concentrate sources of calories) is recommended.
In Summary
Horses are well adapted to thermoregulate during the cold, as long as they can increase feed intake and keep their coat dry
Free-choice access to a hay that is suitable for your horse is is often the easiest, safest, and most effective way to meet increased caloric needs
When free-choice isn’t possible or practical due to management or individual horse health concerns, feeding a couple extra flakes of hay during cold weather and ensuring your horse has access to hay throughout the day can be an option too
Frequently check your horse’s body condition to stay ahead of weight changes
Make sure you’re promoting hydration
Since winter is just a stressor, like other stressors like competition, it makes it extra important for your horse’s foundational nutrition and feeding management to be really solid. So strategies like appropriate forage selection, hay testing, minimizing time without feed, which are all KEY strategies in your horse’s nutrition plan, become extra important in stressful situations like cold weather. Working with your vet and a nutritionist can help you better tailor your horse’s nutrition to them as an individual.
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REFERENCES
Cymbaluk, NF. 1990. Cold housing effects on growth and nutrient demand of young horses. Journal of Animal Science 68(10): 3152-3162.
Cymbaluk, N. 1994. Thermoregulation of horses in cold, winter weather: A review. Livestock Production Science 40 (1994): 65-71.
DeBoer, M., Konop, A., Fisher, B., Martinson, K. 2020. Dry Matter Intake, Body Weight, and Body Condition Scores of Blanketed and Nonblanketed Horses in the Upper Midwest. Journal of Equine Veterinary Science 94(2020): 103239.
Feindt, R. Nd. Managing Cold Stress and Your Horses.
Hammer, C., Gunkelman, M. 2020. Effect of Different Blanket Weights on Surface Temperature of Horses in Cold Climates. Journal of Veterinary Science 85(2020): 102848.
Iowa State Extension Office. Increase Hay Intake for Winter. Accessed online from: Increase Hay Intake for Winter | Equine Science
Jorgensen, GHM., Mejdell, CM., Boe, KE. 2019. The effect of blankets on horse behaviour and preference for shelter in Nordic winter conditions. Applied Animal Behaviour Science 218: 104822.
Mejdell, CM., Jorgensen, GHM., Buvik, T., Torp, T., Boe, KE. 2019. The effect of weather conditions on the preference in horses for wearing blankets. Applied Animal Behaviour Science 212 (2019): 52-57.
Mejdell, CM., Boe, KEB., Jorgensen, GHM. 2020. Caring for the horse in a cold climate - Reviewing principles for thermoregulation and horse preferences. Applied Animal Behaviour Science 232 (2020): 105071.
Morgan, EKM. 1995. Climatic energy demand of horses. Equine Veterinary Journal 27(S18): 396-399
University of Minnesota Extension Office, 2022. Caring for Your Horse in the Winter. Accessed online from: https://extension.umn.edu/horse-care-and-management/caring-your-horse-winter#:~:text=Lower%20critical%20temperature%20and%20energy%20needs&text=For%20every%20degree%20below%2018,will%20keep%20a%20horse%20warmer.
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