Small Changes in Hay Have a Big Impact on Your Horse

102_2349 (Small)You just received a new load of hay in to your barn. It smells so good, and looks just like the last load you got from your regular supplier. But is it really the same? While it might be similar, growing and harvesting conditions vary with every single cutting, and that can have an impact on the nutrition contained in that sweet-smelling pile of bales in front of you.

Generally speaking, the differences aren’t going to be very big – but the next time your horse mysteriously starts losing weight, or losing muscle condition over his topline, you might want to question your hay supplier or get your hay tested.

For example – if your hay got rained on after it was cut, the rain can shatter the leaves, which is where much of the highly digestible protein is found in your hay.  And given how much of your horse’s daily diet is made up of hay, a small decrease in protein can have a big impact.  Let’s take a look at the math behind this:

A 1000 lb horse should eat 1.5-2.0% of its body weight per day in forage – that’s 15-20 lbs!

  • Hay A has 10% protein: 20 lbs of hay x 0.10 protein = 2 lbs of protein intake per day
  • Hay B has 8% protein: 20 lbs of hay x 0.08 protein = 1.6 lbs of protein intake per day

In this scenario, you’d have to feed an extra 5 lbs of Hay B per day to be feeding the same total protein as Hay A provides!

But how much difference does this really make, you ask? If your horse’s intake is already on the low end of protein requirements for his size and activity level, then a 2% drop in hay protein would potentially show up in 2 to 6 weeks. Over that time, all else being consistent, a decrease in general muscle tone, and muscling over the topline, will start to appear. Fortunately, it’s pretty easy to combat – in many cases, simply tossing in an extra flake or two of hay per day, or adding a ration balancer or 1 – 2 lbs of grain per day, at feeding time will combat the decreases – and what horse won’t love you for that?

What are Essential Amino Acids in Protein, and Why Do They Matter?

Nutrition articles frequently refer to protein quality and essential amino acids. When we use the term crude protein, we are essentially talking about a calculation based on measured nitrogen. Protein is about 16% nitrogen by weight, so if we measure the amount of nitrogen and multiply it by 6.25, this gives us a measurement of crude protein. It does not tell us anything about the quality of the protein. If you tested pure nitrogen this way, it would be 625% protein!

Digestible protein is that amount of the protein that is actually digested by the animal. In an over simplified example, if you fed 100 grams of protein and measured 50 grams in the feces, the protein would be 50% digestible.

What is really important to simple stomached animals (horses included) is the content of essential amino acids in the protein. We commonly talk about 10 essential amino acids (EAA), the amino acids that must be in the diet as the animal cannot synthesize them. These are:

  • Phenylalanine
  • Valine
  • Threonine
  • Tryptophan
  • Isoleucine
  • Methionine
  • Histidine
  • Arginine
  • Leucine
  • Lysine

A common memory aid in many nutrition texts books is to use the first letters of these 10 as PVT TIM HALL. (All of you who had a non-ruminant nutrition course still remember this acronym!)

The other 12 amino acids can generally be synthesized in the body and do not need to be in the diet, although there must be a supply of appropriate substrate to produce them. Animal nutrition text books cover this topic in excellent detail.

Limiting Amino Acids

Limiting Amino Acids

When we talk about limiting amino acids, these are the essential amino acids most likely to be restricting the use of the total amount of amino acids present. In most species, lysine is the first limiting amino acid, with methionine and threonine close behind. We commonly talk about amino acids as the building blocks of protein. If you are once you run out of an essential amino acid, you cannot build any more animal protein and the rest of the amino acids are used inefficiently for energy.

If you have a horse on a diet that is calculated to have adequate “crude protein”, but essential amino acids are not present, the horse simply cannot use the protein to build and maintain muscle, hair, hoof and skin and you will see changes in the appearance of the horse, such as loss of muscle mass, rough hair, scaly hoof surface.

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.