How Much Hay Should I Buy for My Horse?

I am frequently asked by horse owners regarding the amount of hay they should purchase for their horse(s). Many owners have plenty of pasture for the summer months and are only concerned with how much they will need to purchase to get through the winter. In this article I will illustrate how I go about determining how much hay needed for my horses.

First of all a mature horse will consume approximately 2% of its body weight in dry matter each day. Growing horses or pregnant horses may require more. You will want to adjust this number a little bit but it does serve as a good rule of thumb. Also, I just assume my horses will eat 100% hay – although I do give them grain and other nutrients. However, by using 2% of their weight I know that I may end up having a little bit too much rather than not enough. I have a place to store it indoors and if I did end up with too much it will easily keep until next winter. Furthermore, it is always easier to get rid of hay in the middle of the winter than it is to buy it.

An average riding horse weighs 1000 pounds and therefore will consume 20 pounds of dry matter per day (1000 * 0.02 = 20). However, everything in the world has water in it, there is nothing that is 100% dry. Even "dry" hay has approximately 10% moisture content,we must adjust for this. Therefore, 22 pounds of hay are required to feed a 1000 pound horse. It is also important to consider that some hay will be wasted, either because of mold during storage, there will be parts of the bale the horse won’t eat, or the horse will turn hay some hay into bedding! A good rule of thumb is to adjust by another 10% to account for this waste thereby resulting in 24 pounds per 1,000 pound horse per day. If you do not feed with a hay feeder then this figure should be adjusted further by at least 10% since more hay will be trampled and wasted by your horse.

However, this does not answer a fundamental question of how many bales of hay are required to feed a horse. The complication here is that not all hay is created equal, bale sizes can differ substantially for both small square bales and large round bales. Hay weight can also vary depending on whether it is purely alfalfa, purely grass, or a mixture of both. Finally, some balers pack hay more tightly than others, really the only way to determine how what baler was used is to ask the supplier.

In general though the following is true:

• Soft Core Round Bales 10-12 lbs/cu ft
• Hard Core Round Bales 12-15 lbs/cu ft
• Small Square Bales 6-8 lbs/cu ft

The differences can be mostly attributed to grass verses alfalfa with grass weighing less than alfalfa.

To determine the amount of cubic feet in a round bale requires the volume equation for a cylinder; V = PI*r²*h where PI = 3.14, r = radius or ½ diameter, h = height (in the case of round bales this is the length – a bale is simply a cylinder laying on its side).

So a bale that is five feet in diameter and five feet in length has a volume of 3.14*2.5²*5=98.125 cu. ft. and since there are 10-12 lbs/cu ft. a soft core round bale will weigh 981 to 1178 pounds, depending on how much grass verses alfalfa it contains. This amount of hay will feed a 1,000 pound horse for 40 to 50 days (simply take 981/24 or 1178/24).

To make life easier on those of you who have no desire to work with the math, I have created the following calculator to help you. Note, this uses the assumptions that I illustrated above and it may not reflect exactly how much hay your horse will eat. Some horses eat more than others and some less. Some horses are pickier and therefore there will be more wasted hay. Also, this assumes you have purchased hay with grasses that are eaten by horses and that is not moldy. However, this calculator has worked very well for me.

Horse Hay Calculator

This calculator makes the following assumptions:

• A horse will consumes 2% of its body weight daily.
• Moisture content of hay is 10% - this is typical.
• 10% of hay is waste, either from spoilage, not desired by horse, or pulled out of the
  feeder and trampled by the horse.
• A feeder is used for large round bales - not using a feeder can significantly increase waste.