Tack n' Talk

Online Equestrian Resource

Hay testing…isn’t it just numbers!

Along with equine nutritionists, I have been going on about testing hay especially for digestible energy.  Over the past few years,  feed companies have been providing quite a bit of information on their labels.  Since we know the grain value, is testing hay now actually important?  Why not just throw your horse 2 flakes of hay during the evening…and call it a day!

It is common sense that the amount of energy your horse needs rises in direct proportion to what you expect him to do, how fast, how long and how hard do you want him to perform. At the lowest end of the spectrum are the horses that are idle, pasture pals, while the opposite end of the scale are racehorses. Your horse more than likely falls somewhere in between.

Please be aware that work isn’t the only element that can raise your horse’s energy requirements above the maintenance level. Environmental conditions, his physical fitness, your horse’s personality, breed type and temperament, and metabolic types are just some of the factors that can play a role in energy requirement. Pregnancy and a horse’s size can also have something to do with energy requirements!  So we need to be aware of many factors when we do our horse’s energy calculations.

Also note that not all the energy contained in the horse’s feed is fully accessible to your horse, Digestible Energy (DE) is what describes the usable portion of total energy, or Gross Energy (GE), so it is very important when you do test your hay to have the testing done for horses.  Do not think that testing is just numbers and by sending it to a cattle lab is good enough!  It is very important to know that DE is the portion of energy which is not lost in the horse’s feces. Please note that DE, however, does not take into account energy lost in urine and energy lost as heat in the actual digestion and absorption of food.

A second way of calculating the energy contents of feed is to use the familiar Calorie count – the amount of heat generated by burning to raise the temperature of a kilogram of water by one degree Celsius. A third way is using total digestible nutrients or TDN. This is generally expressed in either weight or percentages. TDN is the sum of a feed’s digestible carbohydrates, protein and fats multiplied by 2.25 (fats provide about 2.25 times more energy than carbohydrates or proteins). One kg TDN is equal to about 4.4 Mcal (when dealing with large animals including horses, nutritionists generally ugse Megacalorie (Mcal which is 1,000 kilocalories). Note: If you use TDB as your formula you MUST have the TDB value for horses not cattle. Cattle are much more efficient, digestion speaking, than horses so the calculations for energy available from forages (hay) are generally 5 – 15% higher. If you formulate your ration using the cattle TDN, you more than likely will be providing too little feed!

Horses that are nursing, growing, or doing heavy work have relatively high energy requirements.  The list below contains the equations for calculating the energy requirements (DE) for different classes of horses:

  1. Weanling: DE (Mcal/day) = 1.4 + (.0136 x BW) + (4.54 x ADG)
  2. Yearling: DE (Mcal/day) = 1.4 + (.0136 x BW) + (7.27 x ADG)
  3. 2 Yr. Old: DE (Mcal/day) = 1.4 + (.0136 x BW) + (9.1 x ADG)
  4. Maintenance: DE (Mcal/day) = 1.4 + (.0136 x BW)
  5. Early Pregnancy:  DE (Mcal/day) = Maintenance DE
  6. Late Pregnancy: DE (Mcal/day) = Maintenance DE x 1.2
  7. Early lactation: DE (Mcal/day) = (Maintenance DE) + (.04 x BW x 0.36)
  8. Late lactation: DE (Mcal/day) = (Maintenance DE) + (.03 x BW x 0.36)
  9. Light work: DE (Mcal/day) = (Maintenance DE) x 1.25
  10. Moderate work:  DE (Mcal/day) = (Maintenance DE) x 1.50
  11. Heavy work:  DE (Mcal/day) = (Maintenance DE) x 2

Terminology
BW = body weight in pounds.
ADG = the average daily gain (ADG) in pounds per day (weanlings = 1.75 lbs; yearling = 1.25 lbs; 2 year olds = 0.50 lbs).
Early Pregnancy is the first 8 months of pregnacy while the late pregnancy is the last 3 months of pregnancy.
Early lactation is the first 3 months of lactation and late lactation is the second 3 months of lactation.

As a general rule, your horse if given the opportunity,  will choose to eat enough feed to meet their energy needs.   That’s why this writer believes this is one reason to offer your horse hay 24/7!  However, as an example a light-working horse, DE should be 20.5 Mcal/day. From the hay analysis, hay may have .76 to .94 Mcal/pounds or higher of DE.  You can understand why having your hay analyzed is a great idea as it is the only way to determine the actual nutrient content of the hay.  Once this is established you will be sure your horse is consuming an adequate diet and you’ll be able to adjust his hay requirements appropriately.

 

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