The physiology of azoturia is not yet fully understood. However, the condition is characterized by stiffness, pain, and muscle tremor involving the muscles of the hindquarters, except in severe cases where the muscles of the forequarters may be involved as well. Tying-up is a less severe form of azoturia.
Horses worked at irregular intervals and fed high-grain diets are most susceptible to azoturia. Ingested grain is converted to glycogen, which is stored in muscles and elsewhere. If the horses is rested for periods of one or two days whilst on a high-grain diet, large quantities of glycogen are stored in the muscles. Glycogen is used by the muscles as a source of energy when work is being done; the waste product from the chemical change that takes place is lactic acid. If a large volume of glycogen is stored, a large volume of lactic acid is produced when the horse exercises.
If the lactic acid cannot be expelled from the muscle tissue, it damages the muscle fibers, causing the condition known as tying-up. If large areas of muscle fibers are damaged or even destroyed, asoturia results. Some horses that are not on grain diet tie up because they are hypersensitive to lactic acid or because their particular metabolism does not cope with it efficiently.
Some horses seem to be particularly prone to azoturia, and in many cases this is because their muscle cells are not stable, the electrolyte levels that control their permeability being abnormal. Correcting this by giving the horse more or less electrolyte will reduce their susceptibility to azoturia.2
These can vary widely. In mild cases, during or after exercise, the horse steps short in the hindlimbs, giving the appearance of stiffness. In severe cases, the horse will show stiffness, pain, sweating and muscle tremor. The stiffness, involving both the hindlimbs and the frontlimbs, may progress to the point at which the horse cannot move and may lie down. The affected muscles are very hard to the touch, indicating cramp, and the urine may vary in color from dark brown to reddish black, according to the severity of the condition. One important sign is the difficulty the horse may have in passing urine.
Call your veterinarian, who can confirm the condition not only by its history and clinical signs but also by taking a blood count and by doing certain serum enzyme tests.
Stop exercising the horse when you notice that it is tying-up. In all cases except severe ones, walk the horse for thirty minutes. If it appears no better, call your veterinarian. Walking aids in the circulation of blood to the muscles with consequent removal of lactic acid, thus helping to prevent severe cramping.
Keep the horse warm by seeing that it is well rugged. Tempt it with fluids containing electrolytes, which, if drunk in any quantity, will help to flush out the kidneys.
With the aid of information gained form a blood count, the veterinarian can administer a muscle relaxant, diuretics, tranquillizers and anti-inflammatory agents if required, as well as specially prepared fluids and electrolytes by stomach tube or intravenous methods.
All grain should be eliminated from the diet and the horse should be offered a bran mash as a mild laxative. Horses susceptible to frequent tying-up should have a low-level grain diet. Normally the grain level in the diet should be in proportion to the amount of work done. For example, if any one week a horse works for six days, followed by a day off, reduce the quantity of grain in the feed for that day. Recovery can take place within hours, though in severe cases it may take weeks.
Exercise the horse every day, even if it is just walking exercise and consult your veterinarian about the regular use of a particular vitamin supplement as a preventive measure.