Whey Protein for Horses: Benefits & Feeding Guide

Whey protein is a cost-effective, high-quality protein source that is safe to feed to horses. Whey is a common ingredient in commercial horse feeds and is also available as a standalone supplement.

Whey protein is considered a complete protein source for horses because it contains all the essential amino acids that horses cannot synthesize in their body and need to get from the diet. ^[1][2]

Amino acids, which are the building blocks of protein, play a vital role in various physiological processes, including muscle development, tissue repair, and immune function. Adequate protein is also important for hoof health, topline muscles, exercise performance, reproductive health and more.

Whey protein not only provide amino acids, but also contains functional peptides, antioxidants and immunoglobulins which have benefits for horses. ^[3] Feeding whey protein can also help meet the nutritional requirements of lactating mares, growing horses and those in heavy work.

Whey protein should be incorporated as a nutritional supplement alongside a well-balanced diet. The ideal protein levels in a horse’s diet depend on various factors, including age, activity level, breed, and reproductive status.

What is Whey Protein?

Derived from cow’s milk, whey is the fluid that remains after milk is curdled and strained to make cheese. About 15 to 20 percent of whey constitutes protein. This fluid also contains lactose (milk sugar) and milk fat. ^[3]

Whey is not a single protein, but rather a mixture of proteins. The most abundant proteins are β-lactoglobulins (35 – 65% of dry matter), α-lactalbumins (12 – 25%) and serum albumins (5%).

Besides serving as a dietary source of amino acids, some whey proteins or peptides also have bioactive effects – meaning they confer additional health benefits.

For example, β-lactoglobulins can bind retinol (a form of vitamin A) and increase its absorption in the gut. α-lactalbumins bind calcium and other minerals to facilitate their absorption.

Other whey proteins and peptides that have beneficial properties include: ^[3][4]

• • Glycomacropeptide (12%) – a functional peptide that can help regulate appetite

• • Immunoglobulins (8%) – antibodies that can confer protection against microbes such as E. coli and Salmonella

• • Lactoferrin (1%) – binds iron and inhibits bacteria that are dependent on this mineral

• Lactoperoxidase (1%) – enzyme that has antimicrobial effects

The health benefits of various whey proteins have been shown in humans and animal models. More research is needed to assess whether the benefits of whey bioactive proteins would also be seen in horses.

Because protein digestion occurs similarly in horses as in humans and other monogastric animals, ^[5] it is plausible that these benefits would also be found in horses.

Intro to Equine Nutrition

Gain a deeper understanding of your horse's nutrition needs. This free introductory course provides a foundation for horse owners to learn how to balance your horse's diet.

Enroll Now

Types of Whey Protein for Horses

Whey can be processed into various powdered protein-rich supplements for humans and animals. Different formulations vary in their protein content and in how much fat and lactose remains in the product.

Whey Protein Concentrate:

Whey protein concentrate is comprised of whey with the water removed. It retains some lactose, fat, vitamins, and minerals.

The protein content can vary greatly from 34 to 80%. However, standardized products with 80% protein are common. ^[1][6] This is the most cost-effective source of whey and is the form most commonly used in horse supplements.

Whey Protein Isolate:

Whey protein isolate refers to whey fluid that has been microfiltered to remove much of the lactose and fat. The resulting product is almost pure whey protein (90 – 95% protein), with the same amino acid profile as whey protein concentrate. ^[1]

Whey protein isolate is more expensive than whey protein concentrate and is sometimes included in horse supplements or added to their diets on its own.

Whey Protein Hydrolysate:

Whey Protein Hydrolysate refers to protein isolate that is further processed by treating it with several enzymes. The enzymes break down the proteins into fragments of two or three amino acids.

This process improving digestibility and decreasing the allergenicity (allergy risk) of whey proteins. ^[3]

Native Whey Protein:

Native whey protein is a type of whey that is not a byproduct of cheese making. This product consists of whey protein filtered from skim milk that has not been subjected to high temperature pasteurization.

As a result of this processing method, the whey is more intact and may confer greater health benefits in some situations. ^[7] Native whey protein is not commonly used for horses.

Acid whey:

A newer source of whey protein is acid whey, which is a by-product of Greek yogurt and cottage cheese production. It contains functional proteins and peptides, lactose, lipids, vitamins, and minerals. ^[8]

Acid whey is not commonly used for horses.

Nutritional Profile of Whey Protein

The primary reason to supplement whey in your horse’s diet is to increase protein intake. Horses with weak topline or those consuming mature, low-protein forages may need additional protein sources to meet their nutritional requirements and support their health.

Dietary proteins are made up of building blocks called amino acids. These molecules are used by the body for making proteins, hormones, and neurotransmitters.

Amino Acids

There are 21 amino acids, categorized as either essential or non-essential. Essential amino acids must be supplied in the diet because the body can not make them. Non-essential amino acids can be made in the body from other amino acids or other substrates.

Essential Amino Acids

Whey protein is higher in essential amino acids than most other commonly used protein sources. ^[9]

Here are the ten essential amino acids found in whey protein that must be provided through the horse’s diet:

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

The amino acids lysine, methionine, and threonine are often considered the limiting amino acids. They are most likely to be undersupplied in equine diets to the point of limiting protein synthesis in the body.

Leucine, isoleucine and valine are called branched-chain amino acids (BCAAs) based on their chemical structure. These play a crucial role in muscle growth, repair and recovery by stimulating protein synthesis. ^[2]

Whey protein is particularly high in both limiting amino acids and BCAAs, making it a popular protein supplement for athletes.

Conditionally Essential Amino Acids

Conditionally essential amino acids are amino acids that may become necessary in the equine diet under specific circumstances, including periods of rapid growth or during illness. During these times, the horse’s body requires higher levels of these amino acids to support physiological processes and recover from the stressors.

While they can be synthesized by the horse’s body under normal conditions, the increased demand during certain situations may require additional dietary intake to adequately meet nutritional requirements.

Whey protein contains the following conditionally essential amino acids:

• Cysteine
• Glutamine
• Glycine
• Proline
• Serine
• Tyrosine

Whey is especially high in the sulfur-containing amino acid cysteine, which is critical for making glutathione. Glutathione is an antioxidant that is found in all cells of the body and is required to build strong hooves by supporting keratin synthesis.

Non-Essential Amino Acids

Non-essential amino acids can be made from other amino acids or compounds in the equine body and do not need to be supplied by the diet.

Whey protein contains the following non-essential amino acids:

• Alanine
• Aspartic acid (Aspartate)
• Glutamic acid (Glutamate)

Whey vs. Soy Protein

When compared to plant proteins, whey and other animal proteins contain a higher proportion of essential amino acids and BCAAs. However, animal-based proteins are typically more expensive and may be less palatable at high levels of inclusion.

Soybean meal is commonly used as a protein source for horses because it is widely available, cost-effective and is higher in lysine compared to other plant proteins. Soy is often added to feeds intended for performance horses, lactating mares and growing foals to boost the protein content of the diet.

However, whey protein has a more favourable amino acid profile. The following table displays the amino acid content (as a percent of total protein) for whey versus soy protein. ^[9][10]

Branched Chain Amino AcidsOther Essential Amino Acids

Micronutrients

In addition to amino acids, whey protein is a source of essential minerals, including calcium, magnesium, phosphorus, and potassium. ^[6][11]

The levels of these minerals can vary depending on the processing method. In general, whey products that are refined to achieve a higher protein content will have lower mineral content. ^[6]

In six whey protein concentrate samples, the mineral levels varied within the following ranges: ^[6]

• Calcium: 0.2 – 0.67%
• Magnesium: 0.02 – 0.11%
• Potassium: 0.4 – 1.5%
• Sodium: 0.17 – 1.6%

Given that horses have a relatively high requirement for these macrominerals, feeding whey protein supplements is unlikely to meet these needs.

Benefits of Whey for Horses

The benefits of whey protein relate to its high content of essential amino acids as well as the bioactive effects of various constituent proteins. Whey can be used for horses on low protein diets or those with higher protein needs.

1) Supports Horses with a Protein Deficiency

Mature horses at maintenance (not exercising or breeding) can typically meet their protein requirements from forage (hay and/or pasture) alone. However, growing foals, horses in work, lactating mares and mares in late gestation may require added protein sources.

Over time, horses that are consuming diets low in protein will have slower rates of protein synthesis in the body. This can manifest as: ^[12]

• General non-thriftiness
• Decreased appetite
• Weight loss
• Weak, cracked hooves
• Dull coat
• Loss of topline muscle
• Slow growth in foals
• Low milk production

If your horse is showing any of these signs, more dietary protein may be needed. However, before adding more protein consider consulting with your veterinarian to identify any illnesses or underlying conditions that could be causing these issues.

To determine whether your horse’s protein requirements are met, consult with an equine nutritionist to compare the amount of protein supplied by the diet to their nutritional requirement.

A forage analysis is recommended as hay protein content can vary between 5 – 20%. Mature grass hay is likely to be low in protein whereas early maturity legume forages (such as alfalfa) are likely to be high in protein.

If protein is undersupplied, whey protein is a concentrated option with high essential amino acid content.

2) Highly Digestible Protein Source

Whey protein is desirable not only for its amino acid profile, but also because it is easily digested and highly bioavailable.

Proteins in whey are not affected by stomach acid and enter the small intestine largely intact. Enzymes produced by the small intestine and pancreas break down the proteins into single amino acids and peptides (chains of 2-3 amino acids).

In vitro techniques that simulate protein digestion in the gut show that whey protein concentrate is 90% digestible. ^[13] This means that 90% of the protein content is likely to be broken down in the small intestine and available for absorption.

The effect of whey protein on forage digestibility has also been studied. Hindgut microbes are better able to digest low-protein grass hay when whey protein is added to cell cultures. ^[14]

The reason for this could be that the branched-chain amino acids present in whey protein serve as a substrate for the fiber-digesting microbes. ^[14] However, because whey protein is highly digestible in the small intestine, whey protein fed to horses is unlikely to reach the hindgut in large amounts.

3) Improves Diets with Low-Quality Forages

Grass hays typically have a protein content of approximately 11% on a dry matter basis. ^[15] With free-choice access to a hay comprising 10 – 11% crude protein, most horses will be able to meet their protein needs.

However, mature (low-quality) grass hays can be significantly lower in protein content and may not provide sufficient protein, even when offered free-choice.

In general, as grass matures the fibre content increases and the protein content decreases. Your hay is mature and likely has low protein content if it has:

• Coarse, rigid stems
• Few blades or leaves
• Many seedheads visible

Mature, coarse hay might be less palatable and difficult for some horses to eat in large amounts. Combined with the low protein content, horses on a mature grass hay are more likely to experience protein deficiency.

If your forage is less than 8% crude protein, it is likely that your horse will need additional protein sources in their diet.

4) Maintains Protein Intake on a Forage-Restricted Diet

Although free-choice hay intake is optimal for gut health and the psychological well-being of equines, some horses may need restricted access to forage.

Horses that are overweight, have equine metabolic syndrome (EMS) or are prone to laminitis may need reduced energy and sugar intake. One way to do this is to restrict forage intake by eliminating pasture access, rationing hay or using a grazing muzzle or slow-feeder hay net.

It is typically recommended to feed at least 2% of body weight as forage. For horses that need to lose weight or improve insulin sensitivity, forage intake can be restricted to 1.25 – 1.5% of bodyweight, under the supervision of a veterinarian or an equine nutritionist.

Forage restriction is effective for reducing calorie intake, but also decreases protein intake. This can put the horse at risk of protein deficiency, potentially leading to topline muscle loss and weak, cracked hooves.

To maintain protein intake while controlling access to hay, whey protein can be added as a concentrated amino acid source. The amount of whey protein concentrate to add depends on the degree of forage restriction and your horse’s needs.

For example, a 500 kg / 1,100 lb horse fed 7.5 kg of mid-quality hay (1.5% of body weight) would need 100 grams of whey protein concentrate to reach an optimal protein intake.

5) Muscle Development in Growing Horses

Growing horses have a high requirement for dietary protein and amino acids to build muscle mass and support other growing tissues. ^[12]

Whey protein has a similar amino acid profile to muscle protein and is therefore considered an ideal dietary protein for growing animals. ^[9]

Complete feeds designed for foals typically contain 14 – 16% crude protein and use whey protein concentrate as a primary protein source. Studies in piglets show that whey protein supplementation supports lean muscle development in growing animals to a greater extent than soy protein. ^[16]

Because horses and pigs have similar protein digestion in the small intestine, growing foals may also have improved muscle development with whey added to the diet.

6) Helps Build Topline

Low protein intake can lead to weak topline because of slow protein synthesis in muscle tissue. Supplementing with whey can ensure that protein and amino acid requirements are adequately met to encourage topline muscle growth.

However, it is important to note that a weak topline can arise from numerous factors including:

• Gut health issues such as gastric ulcers
• Dental issues
• Old age
• Lack of exercise
• Poor saddle fit
• Health conditions such as PSSM or PPID

If you are concerned about your horse’s topline, consult with your veterinarian to identify and address contributing factors. Changing your horse’s diet and exercise program may help to build topline in your horse.

7) Supports Muscle Recovery after Exercise

Based on studies in humans and other animals, whey protein can support muscle repair after exercise or physical exertion. ^[10][17] It provides the amino acids needed for repairing and rebuilding muscle tissue, helping animals recover faster from workouts and strenuous activities.

This benefit is typically linked to the high BCAA content of whey protein. In particular, leucine stimulates protein synthesis and supports muscle repair following exercise. However, not all studies in humans and animal models show a benefit with BCAA or whey protein supplementation. ^[18][19]

Research in exercising horses

There is a limited number of studies that have investigated BCAA or whey supplementation in horses. So far, supplementing BCAAs in exercise-trained horses has not shown a performance benefit, but may support the immune system and exercise recovery. ^[20]

In the lone study examining the effects of whey protein supplementation on exercising horses, conditioned Thoroughbreds were given either pure leucine or whey protein hydrolysate. ^[21]

The objective of this study was to determine whether leucine or whey protein could elevate plasma insulin levels when combined with glucose. Insulin is a hormone that aids in the storage of glucose as glycogen in the muscles.

The results of this study revealed that leucine increased insulin levels, whereas whey protein did not. Consequently, the efficacy of whey protein supplementation in replenishing glycogen stores in exercising horses remains uncertain. ^[21]

7) Supports Antioxidant Systems

Whey enhances the endogenous production of glutathione, a powerful antioxidant found in all cells of the body. ^[2]

Glutathione and the enzyme glutathione peroxidase are high in the sulfur-containing amino acid cysteine. Because whey is abundant in this amino acid, feeding whey helps support the synthesis of these antioxidants.

Antioxidants neutralize free radicals, which are reactive compounds that are naturally produced during metabolism. If too many free radicals accumulate in cells they can damage DNA, protein, and fats leading to cell death.

Exercising horses experience higher levels of oxidative stress and could benefit from improved antioxidant status. ^[22]

How much Whey Protein to Feed

Most equine diets are significantly oversupplying protein above nutritional requirements, even for performance horses. However, there are some cases in which horses may need additional protein.

How much whey protein to feed will depend largely on the quality of your forage. Horses on pasture have much higher protein intake than those on hay.

As an example, the following table indicates how many grams of whey protein concentrate (80% crude protein) to feed to horses of different physiological states. When the forage is low quality (i.e. 7% crude protein), the amount of WPC to feed is higher than when mid-quality (i.e. 10% crude protein) hay is available.

These diets are formulated for a 500 kg (1,100 lb) horse fed free-choice hay, along with two tablespoons of salt and Mad Barn’s Omneity® to meet vitamin and mineral requirements.

Omneity® P – Pellets

5 stars		85%
4 stars		8%
3 stars		4%
2 stars		1%
1 star		1%

582 Reviews

Learn More

• 100% organic trace minerals
• Complete B-vitamin fortification
• Optimal nutrition balance
• Our best-selling equine vitamin

Note that the sole scientific study conducted on feeding whey to mature horses utilized whey protein hydrolysate. The feeding rate employed in the study was 0.3 grams per kilogram of body weight, which equates to approximately 150 grams per day for a 500 kg (1,100 lb) horse. ^[21]

Larger dosages of whey protein concentrate are needed for gestating and lactating mares if no other protein sources are added to the diet. At higher doses, whey protein may be unpalatable or prohibitively expensive.

When large amounts of supplemental protein are needed, whey protein can be fed along with other common protein sources, including:

• Soybean meal
• Canola meal
• Alfalfa (hay/pellets/cubes)

Considerations when Feeding Whey Protein

Whey protein typically has a mild and slightly sweet flavor, which can be appealing to horses. However, individual preferences vary among horses, just as they do among humans.

When feeding whey protein to your horse, it’s important to consider a few factors to ensure proper usage and integration into their diet. Here are some guidelines to follow:

• Consult with an Equine Nutritionist or Veterinarian: Before adding whey protein or making any significant changes to your horse’s diet, it is recommended to consult with an equine nutritionist or veterinarian. They can provide guidance specific to your horse’s individual needs and determine the appropriate amount and duration of supplementation.
• Choose the right product: Different forms of whey protein are available, including concentrates, isolates, and hydrolysates. Concentrates (80% crude protein) and isolates (90% crude protein) are appropriate for mature horses. Whey protein concentrate with lower protein content is higher in lactose. While likely not a concern for young horses, this may cause digestive issues for mature animals.
• Gradual Introduction: Introduce whey protein to your horse’s diet gradually to allow them to adjust to the new feed over several days or weeks. This helps avoid digestive upset and allows the horse to adapt to the taste and texture of the feed.
• Mix it With Other Feeds: Whey protein can be mixed with other feeds to enhance palatability. You can add it to your horse’s regular grain ration, pelleted feed, or forage. Mix it thoroughly to distribute the whey protein evenly throughout the feed.
• Follow Recommended Dosage: Feed the dosage provided by the manufacturer or advised by your equine nutritionist or veterinarian. The recommended feeding rate will depend on the horse’s size, age, activity level, and specific nutritional needs.
• Monitor the Horse’s Response: Observe your horse closely for any signs of digestive issues or adverse reactions. If your horse shows signs of discomfort, decreased appetite, or unusual behavior, consult your veterinarian immediately.

Remember, whey protein should not replace a well-balanced diet but can be added as necessary. Ensuring an appropriate feeding regimen for your horse requires regular monitoring, periodic reassessment of their nutritional needs, and continuous professional guidance.