Why kidney disease is so difficult to detect in horses

Kidney disease is relatively rare in horses, but its symptoms are often nonspecific and therefore not always immediately recognized, meaning that treatment is often delayed. In many cases, kidney disease is a concomitant or secondary condition of other diseases.

INHALT
The kidney and its functions Causes and classification Symptoms Diagnosis Treatment Forecast Prophylaxis
The kidney and its functions

Horses have two kidneys, each consisting of the renal medulla and renal cortex and surrounded by a capsule. The left kidney is located below the transverse processes of the first lumbar vertebrae, while the right kidney is located slightly further forward, below the last ribs. Along with the liver, intestines, and skin, the kidneys are among the most important detoxification organs in the body. The kidneys excrete waste products and breakdown products from protein metabolism as well as all other toxins. The kidneys also play a key role in fluid and electrolyte balance, the production of vital hormones, and blood pressure regulation. Several thousand liters of blood flow through the kidneys of a horse every day and are filtered there. The end product of filtration in the kidneys is urine, which is excreted via the urinary organs (renal pelvis, ureter, bladder, and urethra).

Diagram of the urinary organs of a horse
1 Kidney | 2 Ureter | 3 Urethra | 4 Bladder
Causes and classification

Kidney disease in horses can have a wide variety of causes. On the one hand, kidney damage can occur secondary to serious infectious diseases, colic, tumorous, muscular, inflammatory, or allergic underlying conditions. However, feeding errors (too much protein), high blood loss, dehydration, toxins, long-term or high-dose medication, or circulatory problems can also strain the kidneys and cause permanent damage. If the kidneys are no longer able to function properly, this is referred to as renal insufficiency.

A distinction is made between acute and chronic renal failure. Acute renal failure describes the sudden onset of impaired kidney function, which is not necessarily accompanied by damage to the kidney tissue. It can be caused by prerenal (upstream of the kidney), renal (within the kidney) or postrenal (downstream of the kidney) factors. Prerenal causes include major acute blood loss, high physical stress, colic, and other gastrointestinal disorders, all of which lead to reduced blood flow to the kidneys due to impaired cardiac output. Renal causes include medications, toxins, and all infectious and non-infectious kidney diseases. Postrenal acute renal failure is caused by an obstruction of the urinary tract and the associated backflow of urine into the kidney. This can be caused by urinary stones, enlargement, injury, or inflammation.

Chronic renal failure is a permanent dysfunction of the kidneys that is always accompanied by damage to the kidney tissue. Unlike the liver, however, the kidneys have very little or no ability to regenerate, meaning that damaged kidney tissue is irreversibly destroyed.

Symptoms

Due to the high compensatory capacity of the kidneys and the initially rather unspecific symptoms, kidney disease in horses often remains undetected for a long time. Only when more than 75% of the total kidney tissue is damaged does kidney disease usually become apparent in the chronic stage through clear clinical signs or changes in the blood count.

The first noticeable symptoms are usually very unspecific. The onset of detoxification disorders can lead to riding problems, tension, behavioral changes, or even perceptual disorders. Undetoxified urea has a narcotic effect and causes the animals to become sluggish and tired.

The characteristic symptoms of chronic kidney disease include frequent urination, which may later become bloody, increased drinking, and weight loss. A dull, lackluster coat and disturbances in the coat change also occur. In addition, fever, weakness, fatigue, loss of appetite, stomach ulcers, and fluid retention in the lower abdomen (edema) are often seen.

Acute kidney failure can develop independently from chronic kidney disease or from the causes mentioned above. Affected horses appear apathetic, can pass little to no urine, and have a rapid pulse. Acute kidney failure is always considered a life-threatening emergency that requires immediate veterinary treatment.

Diagnosis

Although clinical examination and a detailed preliminary report can provide the attending veterinarian with initial indications of kidney disease, an accurate diagnosis and functional analysis of the kidneys can only be made with the help of comprehensive blood and urine tests. The parameters urea (the end product of protein metabolism), creatinine, and certain electrolytes are particularly important for this, but they should always be evaluated by the attending veterinarian in conjunction with all other blood values and the condition of the animal. An additional ultrasound examination can also be used to visualize and assess the position, size, and structure of the organ. This examination can usually only be performed in clinics by specialized veterinarians.

Treatment

In cases of acute inflammation, it is primarily important to stimulate urine production and thus the excretion of toxins by administering appropriate infusion solutions. This is usually done in the form of a continuous drip infusion in a clinic. Herbal active ingredients such as nettle, dandelion, or birch leaves also have diuretic properties and can be used as a complementary treatment.

Anti-inflammatory or antibiotic medications should be avoided as much as possible, as they put additional strain on the kidneys. In the case of bacterial kidney inflammation, the veterinarian will administer an antibiotic that is as gentle on the kidneys as possible.

Due to the irreversible destruction of kidney tissue, chronic kidney disease is incurable. Unfortunately, there is no dialysis available for horses, so rapid intervention is particularly important, especially in view of the low regenerative capacity of the kidneys, in order to preserve and protect the remaining functional kidney tissue as much as possible. Please discuss the exact treatment plan for your individual case with your veterinarian.

In consultation with the veterinarian, the diet of a horse with kidney disease must also be adjusted. In general, great care must be taken to ensure that there are no harmful or toxic substances in roughage or concentrated feed. The animal must have free access to fresh, clean drinking water at all times. To protect the remaining healthy kidney tissue, the feed ration should be low in protein but contain all essential amino acids, which must be supplemented if necessary.

Forecast

Acute renal failure that does not result from a chronic condition is generally curable. The prognosis depends largely on the time of diagnosis and the start of treatment. Chronic renal failure has a significantly poorer prognosis, as kidney tissue that has been destroyed cannot regenerate. With appropriate therapy and adapted feeding and care management, kidney function can be stabilized for a certain period of time.

Prophylaxis

Due to the many different causes, kidney disease in horses cannot be completely prevented. However, a balanced diet tailored to the horse's performance level with a protein content that is not too high and unrestricted access to fresh drinking water can already contribute greatly to ensuring that the kidneys function properly and to preventing possible damage.