What is liver disease and liver failure?
The liver is one of the most important organs in the horse's body. It weighs approximately 5kg and is located centrally within the abdomen. The liver is involved in many essential biological processes, therefore advanced disease where 60-75% of the liver is damaged can be life threatening and will need careful long term management including suitable dietary management. However, under most circumstances the liver can regenerate therefore clinical signs may not always be obvious although athletic performance may be affected.
- What is the liver's role?
- Detoxification and removal of harmful substances
- The ammonia produced from protein metabolism is converted to urea and secreted.
- Bile production and secretion, which breaks down fats
- Destination for the products of digestion
- Defends against disease, especially infections
- Carbohydrate metabolism: Glucose is converted to and stored as glycogen and glycogen is broken down to glucose to help maintain blood sugar levels
- Fat metabolism: Fatty acids are converted to carbohydrates and stored, and fatty acids are exported to fat stores
- Protein metabolism: Almost all of the blood proteins are synthesised in the liver including albumin, fibrinogen and clotting factors
- Vitamin storage of fat soluble vitamins (A, D, K) and vitamin B12.
- Photoactive chemical production: The liver produces chemicals that protect the body from sunlight
- Iron storage
- Signs of liver disease
- Jaundice: May be visible in the horse's mouth, nostrils or eye areas.
- Loss of condition
- Abdominal pain
- Blood clotting may be reduced, leading to excessive bleeding or increased oedemas
- Discoloured urine
- Head pressing
- Decrease appetite or anorexia
- Photosensitivity (sensitivity to UV light)
- Common causes of liver disease
Ragwort poisoning is thought to be the most common cause of liver disease in horses. Although ragwort is most commonly consumed by horses turned out on very sparse pasture, it is much more palatable when dried in hay. Ragwort contains pyrrolizidine alkaloids, which are naturally occurring chemical compounds, which destroy the liver and stop the liver from regenerating.
- Changes to Dietary Advice
Until recently nutritional management of horses and ponies with liver disease has focused on providing a low protein, low oil and often a high starch diet. However as knowledge of liver disease in horses and other species improves, there appears to be little justification for such dramatic adjustments. In fact, dietary adaption is no longer recommended at all in cases of 'compensated' liver disease unless the current diet is significantly over-supplied with protein and/or starch. The following recommendations only relate to horses with severe liver disease showing signs such as weight loss, jaundice and depression or abnormal blood results such as low serum albumin.
- Aim to meet but not exceed protein requirements. Excessive protein intake may be most detrimental in horses/ ponies displaying neurological signs of liver disease such as head pressing. However encouraging individuals to eat may be more important than restricting protein intake
- Providing sufficient levels of quality protein and in particular lysine is still important
- Although high protein ingredients/ feeds such linseed and soya do not need to be avoided completely, seek advice from a nutritionist before adding them to your horse's diet
- Regulating protein intake is thought to be less important for horses showing other clinical signs of impaired liver function
- Excessively restricting protein intake may lead to the breakdown of lean tissue
- Forage should remain the foundation of the horse's diet and ideally be fed ad-lib
- Be cautious of turning out on 'lush pasture' or providing high protein hay/ haylage, particularly in cases showing neurological sigs of liver damage
- Avoid alfalfa hay which is typically high in protein
- Consider having your hay/ haylage analysed; this is the only way to determine nutritional value
- Grazing for several hours (10-14) is encouraged but pasture must be free from ragwort and all other weeds
- Short periods of turnout may encourage horses/ ponies to 'gorge' large amounts of grass which may disturb the microbial population in the hindgut
- Turning out at night may be preferable for photosensitive animals
- Compound Feeds
- Starch intake should be restricted to a maximum of 1g/ kg bodyweight per meal i.e. 500g for a 500kg horse. However other individual requirements may warrant further restriction of starch i.e. those prone to laminitis
- High starch diets may lead to insulin dysfunction which in turn may exacerbate any insulin resistance associated with liver failure
- Divide compound feeds into small, frequent meals (a minimum of 4 but 4-6 ideally) to help maintain blood glucose levels and prevent the breakdown of amino acids in the liver
Oil can be fed at 0.1-1ml/ kg bodyweight per day in the total diet i.e. 50-500mls per day for a 500kg horse provided there are no signs of malabsorption such as diarrhoea or steatorrhea (fat in the faeces) or other contraindications advised by your vet. Any oil should be introduced gradually, adjusting the quantity fed according to the horse's energy requirements.
- Vitamins & Minerals
- Maintain a balanced diet either by feeding the recommended ration of compound feed, broad spectrum vitamin and mineral supplement or balancer
- After providing a balanced diet, avoid additional supplements containing iron and copper
- Reduced absorption and storage of vitamins A, D and E may be a concern in horses with liver insufficiency and therefore increased supplementation (double NRC requirements) may be advisable
- Vitamin C supplementation may be helpful given that the liver is the main site of production
- Additional zinc may also be may also be advisable if plasma levels are low and/ or concentrations of plasma copper are high