A horse’s protein requirement is expressed in the unit Digestible Crude Protein for horses (DCP-h, or in Dutch: VREp). The amount of DCP-h a horse needs differs between mares/geldings and stallions and depends on the horse’s body weight. Sometimes, horses require more protein — for example, to produce milk or to build muscle mass. The standard requirement for a mare or gelding weighing 600 kg is 365 grams of DCP-h. If your horse has poor muscle development, is still growing, is in the last three months of pregnancy, or is nursing a foal, its protein requirement will be higher. You can have your hay tested for protein content using a forage analysis. For feed products such as concentrates or forage replacements, the DCP-h content is usually listed on the packaging.

Providing Extra Protein

If you want to give your horse extra protein, the simplest way to do this is by letting it graze in a pasture. Unfortunately, that’s not possible for everyone or for every horse, and you won’t know exactly how much protein the horse is consuming. Nevertheless, grazing is often the best and fastest way for thin or poorly muscled horses to gain condition. There are many feed sources rich in protein. These may include ingredients like soy or alfalfa (lucerne). Grass pellets are another source of additional protein. There are also individual protein supplements available, made from sources such as spirulina or pea protein.

Soy for Horses?

Soy is a well-known feed ingredient, commonly used in dairy cow rations. It is often included in high-protein horse feed or concentrates. However, soy is not a food that horses naturally consume in large quantities. Moreover, a lot of soy is derived from genetically modified plants, which are resistant to insecticides. The long-term effects of GMOs and insecticides on horse health are not well understood. Finally, soy production is a major driver of deforestation — especially in the rainforest — which contributes to biodiversity loss and has a negative impact on the climate.

Conclusion: Preferably No Soy

Some horses need more protein than their regular diet provides. In some cases, allowing these horses to graze for longer can help, but alternative feed options can also support protein intake. Alfalfa (lucerne) is one option, though it should not be fed in large quantities, and it’s best to avoid very coarse or prickly alfalfa. Large amounts of alfalfa can interfere with magnesium absorption, and prickly alfalfa can irritate the horse’s sensitive stomach lining. Our preference is therefore for grass pellets or specialized protein supplements made from spirulina or pea protein.