In contrast to overfeeding, some horses are not given enough feed for their weight and daily exercise.
Daily rations should therefore be adjusted. (see the clumn "Your horse / Calculate your horse diet).
Some horses are also overfed with regard to protein content.
Excessive protein is particularly harmful to horses.
Protein requirements are generally low (not more than 400 to 700 g of equine digestible nitrogen matter, EDNM, per day for a horse weighing 550 kg exercised for 1 to 1.5 hours a day).
When horses lose weight, the immediate reaction is to increase the feed ration to provide more energy; however, increasing the feed ration very often leads to excessive daily protein intake.
This is true when the protein content exceeds 900 grams of EDNM per day.
This then overburdens the liver and the kidneys which have to filter the excessive protein, transformed into ammonia then into urea.
If the liver continues to be overburdened for several weeks or months, this will cause the horse to lose weight.
Large quantities of excess protein unable to be digested by the enzymatic flora in the small intestine are found in the large intestine, and disrupt the microbial flora. Pathogenic (harmful) flora will then become established in the large intestine, producing amines and Salmonella and Clostridium type toxins which pass into the blood (enterotoxaemia).
This is generally evidenced, in addition to weight-loss problems, by the risk of skin problems, colic, laminitis, poor recovery after exertion and horses which sweat heavily or pass excessive amounts of urine.
Feed quantities should thus be drastically reduced while maintaining forage (5 to 7 kg a day).
You should also ask your veterinary surgeon for advice; the latter may prescribe a hepatic/renal cure for your horse, and analyse the problem if it persists.