Will Whey Protein Improve My Horse’s Topline?

An equine nutrition expert addresses toplines, horse protein needs, and if whey is the way to go.

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Will Whey Protein Improve My Horse's Topline?
If you’re struggling to develop your horse’s topline and feel that there might be a nutrition issue, evaluate your horse’s diet. | iStock

Q: I’ve struggled to build my horse’s topline. His loin is under developed despite being in regular dressage training. A friend at the barn suggested that I add whey protein to his diet. I am curious to learn if this is a good idea and why it might help.

A: Having a strong back musculature, or topline, plays an important role in your horse’s ability to carry you as a rider in a way that a) protects his spine and other tissues and b) allows him to successfully fulfill athletic demands.

Horses can struggle with topline development for many reasons and, while nutrition can play a role, it’s important to rule out other potential issues. For example, saddle fit and training methods can impact a horse’s ability to use himself correctly and, thus, develop strong musculature. Similarly, pain associated with joints or conditions such as polysaccharide storage myopathy might also have an impact. For this reason, I strongly recommend your veterinarian assess your horse to rule out any other issues before assuming it’s nutritional.

I also recommend body condition scoring your horse and make sure he’s not lacking in condition overall. If you determine that the horse is generally underweight, you’ll probably need to increase calorie intake, as this is likely contributing to your lack of topline. If however you determine that the horse generally has good fat cover, the ribs are covered, etc., but his topline is still underdeveloped, then this might be associated with insufficient dietary protein.

How much protein does a horse need?

How much protein a horse needs depends on the horse and the physiologic state. I rarely find a crude protein deficiencies in mature horses’ diets; they typically only require about 10 or 11% crude protein in their diets, which most forage sources easily meet. However young, growing horses require 12 to 14%, and this might pose more of a challenge to meet.

Most good grass hays can meet mature horse protein requirements and provide 10% or higher crude protein; alfalfa typically provides 18% or more. Grain hays such as oat hay can fall short, with an average crude protein of closer to 8%.

In reality, though, your horse doesn’t have a crude protein requirement, but rather an amino acid requirement. Amino acids are the building blocks that make up proteins, and there are 21 amino acids of which nine are essential for mammals (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine with others being conditionally essential). An essential nutrient is one that must be provided by the diet because the animal can’t make that nutrient itself. Each protein contains a range of these various amino acids with some providing a greater proportion of essential amino acids than others. The greater the proportion of essential amino acids in a protein the better quality that protein is said to be.

In an ideal world the amino acid composition of the diet you feed would exactly match the amino acid needs for your horse. Unfortunately, we need more research in this area before we are close to this level of accuracy in equine nutrition, although other species such as swine and poultry, have feeds more along these lines. The amino acid provided in the lowest quantity compared to the animal’s need is said to be the limiting amino acid. For equine diets lysine is typically the limiting amino acid followed by methionine which is why you often see them being singled out on feed labels with guaranteed levels.

Diet Design Tips

Grass hay is made up of medium- or low- quality protein and does not provide a great deal of lysine. This is particularly an issue if you limit your horse’s hay intake. Alfalfa, on the other hand, provides more lysine, so its protein is considered to be of better quality. Many performance horse owners I work with believe that they see a benefit in their horse’s topline when they feed some of the forage ration as alfalfa, and this might be part of the reason.

Another complicating factor associated with hay protein is that the more mature a hay is, the more protein is associated with the structural carbohydrate fractions. This is potentially important because protein digestion and amino acid absorption needs to occur in the small intestine. However, structural carbohydrates require microbial fermentation to be broken down to release the protein contained within. Microbial fermentation occurs in the hindgut, which comes after the small intestine. Therefore, any protein and amino acids released at that point have missed the opportunity to be absorbed and instead are converted by the bacteria to ammonia. So, while a hay analysis can suggest a particular forage has adequate amounts of protein it’s possible that not all that protein is actually available for the horse. This is likely a bigger concern for grass and grain hays because alfalfa has so much more protein and tends to have higher digestibility.

For your horse to be able to synthesize the proteins, he needs the amino acids be present in the right ratio. If one of the necessary amino acids is present at inadequate levels, this will negatively impact protein synthesis. When you combine the issue of protein quality, protein availability, and the concept of limiting amino acids and the need to have the right amino acids present in the right amounts for protein synthesis, it starts to become clear that all these factors play a role in your horse’s ability to generate anything made up of protein.

If your horse’s lack of topline development is due to dietary protein the goal is to improve the overall protein quality of the ration so that more of the essential amino acids are provided in a digestible format. Skeletal muscle is made up of a broad range of amino acids with the greatest being lysine at about 79 mg/g of muscle tissue, followed by leucine at 77 mg/g and the other branch chain amino acids isoleucine and valine.

It might be tempting to supplement individual amino acids; however, I caution against this because amino acids need to be present in a balanced manner. By giving just one amino acid you run the risk of upsetting this balance. Rather, it’s preferable to provide a source of better quality protein that will supply a range of amino acids.

This is why soybean meal is a common ingredient in horse feed. Soybean meal is the highest quality plant based protein source commonly available as a feed ingredient. Soybean meal provides just more than 60 mg of lysine per gram of protein, which is significantly more than a mid-maturity grass hay with 35 mg of lysine per gram of protein, and even alfalfa with 51 mg of lysine per gram of protein. Correctly offering your horse a commercial feed will often ensure he receives adequate lysine, along with other essential amino acids.

whey protein powder
Whey protein comes from milk and is left after manufacturer’s separate curds from it during cheese making. Once carefully dried to a powder, a highly concentrated source of protein remains. | iStock

So, what does all this have to do with whey protein?

Whey protein comes from milk and is left after manufacturer’s separate curds from it during cheese making. Once carefully dried to a powder, a highly concentrated source of protein remains. The protein is also very high-quality with more than 60% of the amino acids being essential amino acids, in particular the branch chain amino acids leucine, isoleucine, and valine. With skeletal muscle being made up of a high concentration of these branch amino acids, adequate branch chain amino acid availability is important for muscle repair after exercise. Supplementing horses with whey protein might help support development of lean muscle mass.

However, research in this area is limited and inconclusive. It’s also important to understand that whey protein comes in several different forms. Most commonly available are whey protein concentrate and whey protein isolate. The concentrate is the whey exactly as it was when the curds were removed meaning that it still contains lactose, fat, and various vitamins and minerals. Protein content can vary widely and care needs to be taken as horses over 3 years old are less able to digest lactose, which can lead to digestive distress. The isolate form is a more consistent product and has had much of the fat and lactose removed. As a result, the product is almost pure whey (90% plus) and is considerably more expensive.

Equine whey protein supplements do exist, and I recommend them over those created for people, because those made for people are often for making protein shakes and contain other ingredients and additives that might not be suitable for your horse.

Take-Home Message

If you’re struggling to develop your horse’s topline and feel that there might be a nutrition issue, evaluate your horse’s diet. Consider the sources of protein in the ration and see whether there are easy affordable steps you can take that will improve the overall protein quality and digestibility of the ration. This ultimately might or might not involve supplementing whey protein.


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Written by:

Clair Thunes, PhD, is an equine nutritionist who owns Clarity Equine Nutrition, based in Gilbert, Arizona. She works as a consultant with owners/trainers and veterinarians across the United States and globally to take the guesswork out of feeding horses and provides services to select companies. As a nutritionist she works with all equids, from WEG competitors to Miniature donkeys and everything in between. Born in England, she earned her undergraduate degree at Edinburgh University, in Scotland, and her master’s and doctorate in nutrition at the University of California, Davis. Growing up, she competed in a wide array of disciplines and was an active member of the U.K. Pony Club. Today, she serves as the district commissioner for the Salt River Pony Club.

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