Horses are not designed ideally to digest meat and animal fats. For one thing, horses don't masticate (chew) effectively to accomplish adequate breakdown of meats. For another, horses have no gallbladder, which is a storage reservoir for bile formed in the liver. One function of bile is to emulsify fats. The liver can only make so much bile on demand, and without the extra bile salts available in a gallbladder, the capacity to digest fats is reduced. Emulsification is the breakdown of fat globules entering the duodenum into tiny droplets in order to provide a larger surface area for enzyme digestion. Lipase (enzyme) secreted by the pancreas breaks the fat droplets down into fatty acids and glycerol for absorption into the lymphatics. So, a meat meal is likely to leave undigested fats in the tract which could cause digestive upsets and interfere with absorption of fat soluble vitamins.
The canine teeth in herbivores like horses are considered to be defensive, and not about mastication. There is nothing else in the dentition of horses that indicates being that of a carnivore or omnivore.
The horse has two stomach compartments unlike a carnivore with only one very large chamber, and in the upper non-glandular squamous portion, the pH is near neutral (7) , which needs to be maintained to prevent ulceration of the vulnerable stomach wall.
Denser feed drops to the lower glandular more acidic portion of the horse's stomach, where pH is 1 to 2 and walls are protected by mucosa.
A meat-eating carnivore with one large stomach compartment can maintain a very acidic gastric pH of 1-2 even while food is present because of the enormous capacity to secrete additional HCL (hydrochloric acid). which would risk acid ulceration of the squamous portion of the equine stomach. This ability to maintain such a low pH throughout the stomach is essential to killing off the huge numbers of pathogenic bacteria ingested in raw eggs or decaying flesh (meat), as well as to facilitate adequate breakdown of the meat proteins.
In addition to plant proteins, horses get their animal proteins from digesting their own gut bacteria, so they don't need meat or dairy as a protein source. The pancreatic and intestinal enzymes that digest proteins (proteases) may or may not be sufficient in horses to break down the proteins in a meat meal.
Blood meal, for example, should not be fed to horses, and feeding eggs or meat is just asking for problems with digestion that may at best cause a minor upset that goes unnoticed, and at worst may result in colic or development of potentially serious infection.
Registered Nurse and 59 years with horses