Protein in Horse Feed & Hay

Newly born, Ella takes in her worldHorses of all ages require adequate amounts of protein for maintenance, growth, reproduction and work, with growth and reproduction being the most critical time periods.  Proteins are important building blocks for body cells.  Feed intake, growth, physical activity, physical endurance, condition, production of milk and fetal development can all be impaired if protein intake is inadequate.

Most every horse owner can name the protein level of the feed they are currently using.  “A 12% sweet feed” is a common answer when asked that question – but how important is that protein percentage?  While the total protein in the horses’ diet is important, horses actually require essential amino acids, even though crude protein is what is required by law to be listed in a guaranteed analysis.  Many feed manufacturers are moving towards listing the amino acids on the tag, which can help horse owners to see the quality of the protein sources being used.

Beyond the grain portion of the diet, a major factor to watch for regarding protein in an equine diet is the hay source.  After all, hay makes up the majority of the diet, and thus a lot of the protein in the diet comes from the hay. Horse owners need to figure in what their hay sources are providing, and balance it together with their grain source, to determine what their horses are consuming.

Listed below are protein percentages required by the major categories of horses – please note that these are for the TOTAL DIET, not just the grain portion.

  • Foals: 16-18%
  • Weanlings: 14-16%
  • Yearlings: 12-14%
  • Mature horses: 10-12%
  • Lactating mares: 12-14%

In order to figure out the total protein in your horses’ diet, follow this simple calculation:

( (Lbs Hay x Protein in Hay) + (Lbs Grain x Protein in Grain) ) / Total Lbs Fed = Protein in Total Diet

To have an accurate estimate of protein in your hay, it is best to have it tested.  Check with your local extension office or feed store for labs in your area that will do the testing.  Hay protein can vary dramatically from one cutting to the next, and from one field to the next.  Rainfall, stage of growth when harvested, and a variety of other factors can also influence the quality of the hay.  Alfalfa hays are typically considered to be higher protein that timothy or other grass hays, however if alfalfa is harvested late, perhaps due to weather concerns that make it tough to get in the field, it can have lower proteins than some grass hays that are harvested at the proper time.  Thus, it is always a good idea to know the facts behind your hay source rather than “guesstimating”.

A final point that must be made about protein:  Increased protein levels are not generally responsible for a “hot” horse.  Protein is a very inefficient source of energy, and its main use in a mature horse is the re-building of muscle and other body cells after exercise.  Instead, it is the starch and sugars in a horses diet, as well as the calorie intake to calories used (exercise level) ratio, that are primarily responsible for a “hot” horse.  But that’s a topic for another blog post!

Amino Acids in Horse Feeds

Limiting Amino Acids

Most horse owners can quickly tell you the crude protein level in the feed they are giving their horses.  But, what horse owners really need to know about, is the amino acid content.  Protein is made up of amino acids – similar to how a chain is made up of links.  There are two basic categories of amino acids: essential and non-essential.  Essential amino acids must be provided in the diet, as the horse cannot manufacture them on their own in the digestive tract, where the non-essential amino acids can be manufactured.

There is another key thing to know when it comes to amino acids – there are “limiting” amino acids.  This means that if a horse runs out of a “limiting” amino acid, it can’t utilize any of the remaining amino acids present in the feed.  If the horse has enough of the first most limiting amino acid, but then runs out of the second most limiting amino acid, it can’t use the remaining amount of the third most limiting, and so on.

In horses, the first three most limiting amino acids, in order, are lysine, methionine, and threonine.  Generally speaking, if these three amino acids are present in sufficient quantities, the ingredients used to provide them also provide the remaining amino acids in sufficient quantities.  It is becoming increasingly common to see these three listed on the guaranteed analysis of horse feed tags, as it is an indication of the quality of the protein sources and the balanced nature of the feed.