Illini HorseNet Papers
Illinois winters can be unpredictable. Prolonged periods of rather mild seasonal temperatures may be punctuated by brief or extended periods of extreme cold and/or wind. During these "cold snaps", your horse's diet should be adjusted to meet the extra energy demands of maintaining normal body temperature.
Increase dietary energy when the external temperature is below the horse's lower critical temperature The external environmental temperature at which the horse's body requires extra energy for temperature maintenance is called the lower critical temperature. At ambient temperatures below the lower critical temperature, body functions such as growth and weight gain may be compromised without extra dietary energy. For most horses, this lower critical temperature is estimated to be about 45°F. During windy days, the wind chill temperature should be used to assess whether or not the lower critical temperature has been reached, rather than simply the ambient air temperature. Several different factors including humidity, wind, rain, sun and snow, coat thickness and relative dryness combine to affect a horse's true lower critical temperature. When the horse's hair coat becomes wet, the lower critical temperature may increase by as much as 10 to 15°F.
The dietary energy required for supporting various body functions including temperature maintenance, growth, lactation, pregnancy and exercise is expressed as mega calories (Mcal) of digestible energy (DE). For each 1°F decrease below the lower critical temperature, the horse requires a 1% increase in digestible energy to maintain normal body temperature. The following formula may be used to calculate the increased DE requirement for a horse as a result of cold temperatures and wet, windy conditions: critical temperature - actual temperature = % increase in DE required.
Example: Here is an example of adjusting dietary energy intake for an 1100 pound pregnant broodmare during the 10th month of gestation, housed outdoors, during dry weather with an air temperature of 25°F and a wind chill that results in an actual temperature of 15°F.
Step 1. Subtract the actual temperature (including the wind-chill adjustment) from the critical temperature (accounting for wet conditions if necessary): 45°F - 15°F = 30°F, equivalent to a 30% increase in DE requirements.
Step 2. Because an 1100-pound pregnant mare in the 10th month of gestation requires 18.5 Mcal of DE per day (see Feedstuffs annual Reference Issue and Buyers Guide) and because the horse in this example requires a 30% increase in DE, do the following calculations: 18.5 Mcal x 30% = +5.5 Mcal increase. The dietary energy requirement is therefore: 18.5 Mcal + 5.5 Mcal = 24 Mcal DE/day.
Step 3. Next, determine the amount of feed necessary to supply these increased calories. A 1,100-pound mare will typically consume about 19 pounds of ration daily (about 1.7% of her body weight) under thermo neutral conditions. Because the recommended DE concentration of the ration (grain mix plus forage) fed to this mare should be about .90 Mcal DE/lb of feed (see Feedstuffs annual Reference Issue and Buyers Guide), we can calculate the increase in feed as follows: 5.5 Mcal ÷ .90 Mcal/lb of feed = 6.1 pounds of additional feed to provide the 24 Mcal DE/day needed under the cold conditions defined in the example.
Step 4. Determine the total amount of feed the horse requires by adding the 6.1 pounds of additional feed to the 19 pounds of feed the horse requires under normal conditions: 19.0 + 6.1 = 25.1 pounds per day of total ration.
General nutrition management tips for horses during cold weather:
- Monitor your horse's body condition frequently during cold weather. Thick winter hair may obscure poor body condition, and the need for additional dietary energy. However, do not over feed horses that are obese.
- Feed more hay than grain for horses in good body condition. The heat of digestion is greater for hay than for grains, because hay is digested with the help of microbes in the horse's cecum and colon, and these organisms give off metabolic heat that helps to keep the horse warm. Horses in good flesh can use the extra heat from digesting hay, but don't need the extra calories from starchy grains that may add to obesity problems.
- Increase both the hay and concentrate intake for horses that are below average body condition. These horses need both the extra heat from forage digestion and extra calories from starchy grains in order to gain weight and improve body condition. Horses in especially poor condition may need even more calories in the form of added dietary fats and oils.
- Provide 10-12 gallons of warmed water to each adult horse per day. Many horses will not drink sufficient water to allow for adequate feed intake and for normal body functions if the water is near freezing. Most horses will begin to drink less water than is recommended when the water temperature is below 45° F and they prefer the water temperature to be about 65° F. Impaction colic may result when horses consume dry feeds and do not consume adequate water.
- Feed the grain mix in the form of a wet mash during very cold weather. Offering the horse's typical grain concentrate as a wet mixture with warm water is one way to increase water consumption in horses that are reluctant to drink during cold weather.
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