How Much Hay is Wasted?

When a small square bale is open, it falls naturally into individual flakes.

When a small square bale is open, it falls naturally into individual flakes.

Have you ever had the job of feeding hay to a barn full of horses? A common method of feeding hay to horses is to simply toss flakes of hay on the ground. The horses lower their heads and don’t stop eating until it’s all gone—or trampled into the ground. If you’ve ever mucked out a stall or seen a well-used paddock you know—there’s a lot of wasted hay when its fed on the ground.

As one of the researchers, Kr­is­hona Martin­son put it, “If you drop a large round bale on the ground it just be­comes this happy hay fort for your horses. They walk in it, they lay in it, they pee in it, they poop in it.”

Horse Talk – flake: A flake of hay is a section of a square bale (the way it just naturally divides as in the photo above).

Up until recently, no research had been done to find out how much hay is wasted when small square-bales are fed in outdoor paddocks. Kr­is­hona and her fellow researchers at the University of Minnesota wanted to find out.

They designed a study to determine how much hay is wasted, herd bodyweight change, how much hay is eaten, and whether using small square-bale feeders for the outdoor feeding of adult horses is worth the money.

Click to enlarge

Click to enlarge

Three feeder designs were chosen for the study.

a hayrack (shown on the right) that cost $280;

a slat feeder (middle) priced at $349;

and basket feeder (left), that cost $372

A no-feeder control (hay fed on the ground) was also evaluated.

1. What was the range in price, from the least expensive to the most expensive hay feeder?

2. How much do these feeders cost altogether?

The Method

3 horses feeding from hay feeder

Three of the test horses eating hay from the basket feeder.

Two feeders of each type were placed in separate, outdoor, dirt paddocks. Twelve adult horses were divided into four similar herds with an equal number of horses in each herd. The herds were rotated through the four paddocks (one had no feeder). They remained in each paddock for a period of seven days.

3. How many horses were in each herd?

4. How many days would it take for one complete rotation through all four paddocks?

Horses were weighed using a scale before and after each rotation, and the weights added together to give the herd bodyweight. The difference between the before and after weights was called herd bodyweight change.

Imagine you are one of the researchers. It is your job to weigh the horses in one herd, and calculate the herd bodyweight and the herd bodyweight change.

Before releasing them into one of the paddocks each horse steps on the livestock scale. You take the following readings: 1,050 lb (476 kg), 1,160 lb (526 kg), 1,110 lb (504 kg)

5. Calculate the herd bodyweight for this herd.

6. How would you calculate the herd bodyweight change?

A test horse eating out of the hayrack feeder.

A test horse eats out of the hayrack feeder.

For this experiment, grass hay was fed at 2.5% of the herd bodyweight split evenly between two feedings at 8:00 am and 4:00 pm.

7. How much time was there between the morning and afternoon feedings?

8. How much time was there between the afternoon feeding and the morning feeding the following day? 

9. How much hay in total would you feed the herd you weighed?

10. How much hay will you feed at each feeding?

Before each feeding, any hay left on the ground from the previous feeding, referred to as ‘Hay Waste,’ (HW), was cleaned up. Any hay left inside a feeder was also collected. This leftover hay was referred to as orts (O).

Science Talk – orts: a scrap or remainder of food from a meal.

What did the researchers find?

Click to enlarge

Click to enlarge

The table to the left shows the researcher’s calculations based on what they observed and the data they collected. The percent hay waste (HW%) was calculated as the amount of hay waste (HW) divided by the amount of hay fed (HF) minus orts (O). 

Estimated hay intake (EHI) was estimated as the amount of hay fed (HF) minus orts (O) and hay waste (HW).



11. Write the calculation for percent hay waste as a math equation.

12. Write the calculation for percent estimated hay intake as a math equation. 



A large bale fed on the ground.

A large round bale fed on the ground.

Referring to the table above:

13. Which feeding method resulted in the most hay being wasted?

14. Which feeder resulted the least amount of waste?

15. In which column do you find negative numbers?

16. What do these negative numbers tell you about the change in weight of the horses during that week?

17. Which feeding method resulted in the most weight gained over the test week?

Understanding math and science is helpful when managing a stable. Now that you know how to reduce hay waste, if you managed a barn, which feeding method would you choose?

Common Core:
3.NBT.A.2 – 3.NBT.A.2 Fluently add and subtract within 1000 using strategies and algorithms based on place value, properties of operations, and/or the relationship between addition and subtraction.
4.OA.A – Use the four operations with whole numbers to solve problems.
4.MD.A.2 – Elapsed time: word problems
5.NBT.B.7 – Multiply a decimal by a multi-digit whole number
6.NS.B.3 – Fluently add, subtract, multiply, and divide multi-digit decimals using the standard algorithm for each operation.
6.EE.B.6 – Use variables to represent numbers and write expressions when solving a real-world or mathematical problem
6.RP.A.3c – Find a percent of a quantity as a rate per 100

By Deborah Stacey; CC BY 2.0
All other photos courtesy of Krishona Martinson, PhD, University of Minnesota Horse Extension Program

Icon made by Freepik from is licensed under CC BY 3.0

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3 Responses to “How Much Hay is Wasted?”

  1. Esther
    February 15, 2017 at 9:50 am #

    We really enjoyed doing this post of the week since we have horses we keep and feed hay outside to. As of now, we don’t use any feeders. So it was interesting to find out how much hay is going to waste. My daughter’s question though is: if the slat feeder had the least amount of hay waste, why did the herd still loose 7 pounds? It logically does not make sense.

    • HLM
      February 15, 2017 at 2:11 pm #

      Thanks for this great question! I’m going to contact the researchers and see if they can provide an explanation. If they do—I’ll be sure to post their response and let you know.

      That is exactly the kind of question a scientist would ask—then develop an experiment to try and determine the answer!

  2. HLM
    February 15, 2017 at 7:13 pm #

    One of the researchers, Krishona Martinson, was kind enough to respond to Esther’s question!
    “The slat feeder presented the greatest barrier to consuming hay compared to the other feeders; therefore, the horses were not able to consume all of their hay meal between the morning (8:00 am) and afternoon (4:00 pm) which resulted in orts (remaining hay) being collected from inside the feeder each afternoon. However, given an equal amount of time between feedings (i.e. 12 hours), horses would likely have been able to consume their entire hay meal from the slat feeder. Herds (3 horses) lost small amounts of bodyweight when feeding from the slat feeder because they did not have sufficient time to eat their hay meal. Remember, the 7 pounds was the sum of all three horses. Although this weight loss was statistically significant, its likely not biologically significant to the horse. You can read more at:”

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