All Flakes of Hay are Not Created Equal

I was called out to farm to review a horse that had started to lose weight.  The owner explained to me that the horse had been diagnosed with ulcers, so her vet recommended alfalfa hay. She purchased some nice quality second cutting, and had the test results which showed the hay to be exceptional quality, and containing 1Mcal (1000 calories) per pound. Thus, she could not figure out where the hole in the feeding program was that was causing the horse to lose weight. 

In review, her horses diet was calculated at 21.5 Mcal per day, based on his work schedule and body condition score:

  • 4 flakes of timothy hay per day
  • 4 pounds of grain  per day

Since the horse weighed in at 1000 pounds, we chose to go with 2% of his body weight per day in forage, or 20 pounds.  The old hay had tested at 800 calories per pound. We balanced the diet with 4 pounds of grain at 1430 calories per pound, or 1.43 Mcal.

  • Forage = 16 Mcal
  • Grain = 5.7 Mcal
  • Total = 21 .7 Mcal

The owner explained that she was feeding the same amount of hay as before, and since it was such good quality, it had to be a grain problem.

When we calculated his old diet, each flake of hay averaged 5 pounds each.  That was how we determined 4 flakes would reach the 2% or 20 pound feed rate.  I asked if she had weighed the new hay, and she admitted she had not done so yet.

To her surprise, when we weighed several flakes, they all averaged 3 pounds per flake.  When I showed her the math, the problem was obvious:

  • 1 Flake timothy hay 5lb@ x 4 flakes per day = 20 pounds per day x 800 calories = 16Mcal  (16,000 calories)
  • 1 Flake Alfalfa hay 3lb@ x 4 flakes per day = 12 pounds per day x 1000 calories = 12Mcal (12,000 calories)

With that simple change in hay, she had cut her horse’s caloric intake by 4,000 calories per day over the past month. Armed with this new information, adding more flakes of hay to the daily ration put the horse right back on track.

Why did my horse lose weight during the hot weather?

Several factors influence how much energy it takes to maintain normal body temperature.   Air temperature, humidity, wind velocity, solar radiation and precipitation are all factors that affect how much energy is expended to maintain normal temperature for animals that are exposed to these elements.

We know that horses use more Calories to stay warm in the winter as cold weather has been estimated to increase Digestible Energy requirement about 2.5% for each degree Centigrade below  -10 C (14 degrees Fahrenheit) per the 2007 NRC Nutrient Requirements of Horses, page 10-11.  The “thermal neutral zone” for horses is estimated to be from about 5 degrees C/ 40 degrees F (Lower Critical Temperature) to 25 degrees C/77 degrees F (Upper Critical Temperature).  

It takes horses 21 days to adjust to a higher or lower ambient temperature, with most of the adjustment taking place in 10-14 days and more adjustment taking place over a longer time, so the actual range may depend on what the horse has acclimated to over longer periods of time. 

We do not have good horse data for the impact of temperatures above the Upper Critical Temperature.  If we assume even a 0.5% increase in DE for each degree C above the Upper Critical Temperature (a fairly conservative estimate based on known cold weather changes and other species information), then if the ambient temperature is 35 degrees C/95 degrees F, we would need 5% more DE at the higher temperature just to maintain body weight.  As most horses do not eat more at higher temperatures and may actually consume less, the higher DE requirement for just maintenance might be expected to produce an actual weight loss just from the extra energy required to keep cool. 

Higher ambient temperatures also increase daily water requirements, particularly if horses are working.  The increase can easily be 50 to 100% higher, depending on the combination of factors present on a given day.  If they do not get enough water, they may also lose weight.

To put it in a human perspective, I was judging horse shows this summer when it was 95 to 100 degrees F, 80+% humidity, very little breeze and bright sun.  In addition to a bit of sunburn, I lost some weight and required 24-48 hours to get fully rehydrated even while drinking water all day!

Activity Levels for Horse Feed Directions

When feed companies formulate horse feeds, one of the steps involved is determining how much of a particular feed a horse would need to eat. Within that, horses of different activity levels will require different amounts of feed to meet their varying calorie and nutrient needs. The video below gives a short description of each of the activity levels listed on feeding directions, to help horse owners feed their horses properly.