top of page

Why Feed More Than Hay? Part III: Protein

Updated: Nov 25, 2022

As expected, the high cost of fertilizer this year has resulted in lower protein levels across forage sources. Therefore, this is a super time to discuss the third reason to feed your horse more than hay or pasture; for protein quantity and quality. How do you ensure that your horse does not suffer from protein deficiency in the coming months?


If you have not already read "Why Feed More Than Hay Part 1: Calories" and "Why Feed More Than Hay?: Part II: Viramins and Minerals", you might want to come back to these links.

There was a time in my career, that I didn't think much about adding protein to horse diets. If you look at the crude protein requirements of an average 500 kg (1,100 lb) mature horse in moderate work, it's only about 768 grams of crude protein (National Research Council, 2007). At 2% of body weight intake, that could easily be met with an 8% crude protein forage source. However, over the years, as I've consulted with more and more performance horses of every discipline at every corner of the USA and gained new knowledge from my nutritionist mentors, I've changed my mind.


The first thing that you need to know is that the CRUDE PROTEIN test is just that...crude. It gives you some estimate of quantity, but no estimate of quality. Crude protein analysis of feedstuffs is a simple estimation of nitrogen content. That means the information coming back to you is about how much nitrogen is in the sample. The trouble is that we don't know what that nitrogen is attached to- even motor oil, wood shavings, and the bottom of my shoe have a crude protein level! When you submit a sample for analysis they will either break down the sample and extract each nutritional component (wet chemistry), or they will shine light waves at the sample and see what bounces back, relate it to an equation, and spit out a rough crude protein estimate. Most of you will pay for the light waves method, known as Near Infrared Spectroscopy (NIR), because it's cheaper. There are some forages and feedstuffs that this is an exceptionally useful tool, but when it comes to mixed grass hay, the reliability of these light wave estimates breaks down. All of this is to say, that an 8% crude protein forage may NOT actually be meeting your horse's protein requirements. This is especially true if your horse is an active performance horse, suffers from myopathy, is older, younger, or lactating!


Protein Quantity

The next useful thing for you to know are the averages! Let's start with grass hays, since they are the most variable and often the ones lacking in crude protein quantity and quality. If you look at all Equi-Analytical's Common Feed Profiles database (accessed on October 21, 2022) of over 106,725 grass hay samples taken from all over the USA between 2004 and 2022, you see that the average crude protein is about 11%. That more than meets the average horse's protein requirements when fed at 22 lbs per day. However, problems might arise when the crude protein level falls significantly below that for several categories of horses; high performance, myopathy, senior horses, young horses and lactating horses. Poor quantity and quality of protein can lead to poor toplines, potbellies, stunted growth, muscle atrophy, lack of stamina, and even developmental joint disorders in young horses. In the last few months, I've seen a 5% crude protein hay that was being fed to performance horses and seniors, and a 7% crude protein hay being fed to lactating mares and foals. So, definitely something worth knowing, right!?! (See test results below.)


Reasons for low crude protein grass hays include the following...

  1. The farmer cut the field at a very mature stage.

  2. Poor soil quality

  3. The farmer did not fertilize appropriately.

  4. Unfavorable weather conditions.

  5. Long term storage of hay.

Poor quantity and quality of protein can lead to potbellies, stunted growth, muscle atrophy, muscle soreness, lack of stamina, and even developmental joint disorders in young horses.

Now let's compare the average grass hay to an alfalfa-grass mix hay that I was presented with recently! I was quite shocked when I received the forage test back for a local sample. The crude protein on this roughly 50:50 alfalfa-grass hay was only 9.2%! Considering that full alfalfa hay averages about 18-21% crude protein, I would expect a typical 50:50 blend to be between 12-16% crude protein. The relatively low crude protein in this haystack says something about the methods the farmer used to grow the forage. Likely there was too little fertilizer added. Since this forage was being fed to multiple broodmares at peak lactation and expecting to be bred back, it was very good that the owner got this forage analysis done. We were able to fortify the diet with a mare and foal feed and a ration balancer.

Protein Quality

The last thing that I'd like to touch on about protein is the QUALITY of that protein. The quality of protein in a forage or feedstuff is determined by the blend and ratio of various amino acids. You might have heard of the limiting amino acids lysine, methionine and threonine, or maybe one of the other essential amino acids such as glutamine, carnitine, leucine, valine, ect. One way that we can estimate protein quality is to look at the Lysine content of our forage source. That average 500 kg (1,100 lb) mature horse in moderate work needs a minimum of 33 grams of lysine per day which is the limiting amino acid for horses. In the above grass hay samples, we have 0.18 and 0.26% lysine which means your horse would consume only 18 grams or 26 grams, respectively, of lysine when eating 22 lbs of either hay. This is way too low for my comfort, and why I am such a huge fan of ration balancers that have a significant amount of crude protein and lysine in them (25-35% crude protein).

Some nutritionists even question the quality of protein in alfalfa hay, arguing that the blend of amino acids may not be optimal for an equine athlete performing at very competitive levels or for horses suffering from myopathy (i.e. PSSM, RER, HYPP, ect). This is why I refer to the additional protein in a fortified feed product as "cheap insurance". As your hay or pasture quality varies from year to year, cutting to cutting, and even bale to bale, it gives me great confidence to add a little protein "insurance" in the form of a ration balancer, performance or senior feed or other amino acid supplement. In addition, even when fed very good quality hay, there is evidence that supplementation with branched chain amino acids is beneficial to elite sport horses and those with myopathy. I won't expand on this here, but you can can check out a recent article called "Performance Boosting Supplements: What are they and do they work?" by CLICKING HERE.

How to Prevent Protein Deficiency

So, the big question likely bouncing around in your brain right now, is how do you know if your horse has a protein quality or quantity deficiency? The simple answer is to get a forage test done. There are three steps; 1) obtain a representative sample of your forage source, 2) send to an appropriate lab, and 3) interpret the results by comparing them to your horse's needs. The first step is the hardest, and definitely requires the most "activation energy". You'll need to find a forage probe to take a great series of samples! You can buy these probes online for roughly $120-$180, borrow one from your county's conservation district or land grant university extension office, borrow from a friend, or have a feed/supplement rep come out and do one for you. Once you acquire a forage probe and take 10-12 representative samples, it's easy to mail into a lab (I prefer Equi-Analtyical), and then receive the results. Then, reread this article!


As you have now learned, protein is a good reason to feed your horse something other than just hay or pasture. After calories, vitamins and minerals, it's the next most common reason to compliment a forage source. Which fortified feed, high protein commodity, or supplement you use depends on your horse's needs. More specifically, the most appropriate protein rich product will depend on the difference between your forage quality and your horse's performance level. If you need some ideas for protein sources, you can contact Natalie for a private nutrition consult. Start with a FREE 15 Minute Discovery Call.




454 views0 comments

Related Posts

See All
bottom of page