Feeding A Horse With Liver Damage

The liver is the largest gland in the body, weighing on average between 5 - 9kg depending upon the size of the horse. It is situated immediately behind the diaphragm and in front of the stomach and it is held in position by six ligaments and the pressure of the surrounding organs. It is one of the accessory glands of the digestive system, the others being the pancreas and the salivary glands. At cellular level the liver is a simple organ made up of identical functional cells called hepatocytes, which act identically to the liver as a whole. These cells are continually metabolically active.

It is thought that the liver has over 100 different functions, which can be divided in to 5 basic categories:

• Digestive and secretory function: The liver produces bile, which is necessary for fat digestion and neutralization of the small intestinal contents. The horse has no gall bladder and the bile duct is wide to compensate for this. Bile is therefore continually produced in a dilute form and carried through the liver via the bile duct. The bile duct branches through the liver tissues and carries not only bile, but many waste metabolites, including hormones and enzymes.
• Metabolic function (CHO, Protein, Fat metabolism): The liver is the main store of utilizable energy. After a meal has been eaten glucose is absorbed and stored as glycogen in the liver and muscles. When blood glucose drops glycogen is mobilized and when blood glucose rises glycogen is deposited. This is mediated by several hormones including insulin. The liver is also involved in the metabolism of lipids. When the horse is using its fat stores as a major energy source e.g. Starvation or when energy requirements exceed energy intake, large amounts of fat appears in the liver. Accumulation of fat in the liver is a sign of rapid fat mobilization in preparation for its metabolism to provide energy. In well-fed horses protein intake often exceeds protein requirement. The liver is able to breakdown excess amino acids and non-essential amino acids. When the liver breaks down the amino acids it removes the amino group, which is excreted as urea and the remaining carbon structure can be used as an energy source, although this is not highly recommended!
• Synthetic function (Clotting factors, proteins): The liver is a major player in the manufacture of almost all the major plasma proteins and low volume proteins such as clotting factors.
• Storage function (Vitamins & minerals etc): The liver is a vital storage organ for minerals such as iron and copper as well as vitamins (Vitamin A, D, and B12) and other proteins.
• Detoxification: The detoxification function is directed firstly at possible toxic substances absorbed from the intestinal tract. These are delivered to the liver by the portal blood system and therefore pass the liver first before entering the general circulation. The liver filters the toxins out so that they cannot gain access to other tissues. Some of these toxins can cause damage to the liver itself e.g. Ragwort in horses.

What can go wrong?

When many other organs are damaged it usually means that cells are completely destroyed with total loss of function. Most, however, can repair and regenerate within reason but in the case of the liver it is far more complex!! Anything less than complete destruction of the cells results in a variety of deficits and damage may result in reduced synthetic function but the only sign maybe a drop in blood proteins, which is not bad enough to assume liver damage.

The common features of liver disease include:

Weight Loss
– Lethargy / depression
– Ascites / peripheral oedema
– Haemorrhagic diathesis
– Icterus
– Soft Faeces
– Photosensitisation
– Hepatic encephalopathy
– Failure of anabolic function
– Failure of synthetic function

Over the past few years the number of deaths due to ragwort poisoning has increased dramatically. Acute, severe poisoning from ragwort is rare, since it is unpalatable and rarely eaten by choice and more often it is the small but frequent ingestion of Ragwort poison causing repeated and minor damage to the liver over a period of time. Ingestion of Ragwort will result in ingestion of the pyrrolizidine alkaloid, which passes to the liver via the hepatic portal vein. On arrival the toxin starts to damage the hepatocytes, eventually leading to shrinking and progressive fibrosis of the liver. Clinical signs will show once more than 75% of the liver is damaged. Liver failure cannot be treated and only nutritional assistance can be provided to assist with regeneration. The best nutritional management that can be given is prevention rather than cure!

For horses suffering from liver damage nutritional therapy involves:

• High CHO diets: Readily digestible carbohydrate sources e.g. Oats are readily utilized to provide glucose and decrease the need for the liver to manufacture glucose. Remember that feeding soluble carbohydrates should be done with care to reduce starch overload, so frequent small feeds are recommended. For liver damage, it is usually suggested that between 5-6 small feeds are given to help prevent peaks and troughs in blood glucose levels.
• Low but quality protein sources: Ammonia build up needs to be reduced so protein intake needs to be monitored but essential and branched chain amino acids need to be provided. Branched chain amino acids (BCAA’s) may help with some of the neurological symptoms of liver damage and because they are essential amino acids they are not extensively taken up by the liver. Feeding additional BCAA’s also seems to improve the attitude of the horse. Feeds such as molassed sugar beet pulp and maize are high in BCAA’s and therefore a good inclusion in to the diet of a liver damaged horse.
  
• Quality forages: Good quality forage is essential for any horse to ensure a healthy digestive system and to satisfy the horses need to chew and for saliva production. Firstly horses should be encouraged to graze, as pasture is a rich source of vitamin E, which helps to support immune function. At all other times access to hay should be provided. Horses with liver damage require forage of low to medium quality protein but it must be hygienic ally clean and legume forages, such as alfalfa should be avoided. Horses with liver damage often have poor appetites so hay can be dampened with some diluted molasses to improve consumption and it is sometimes better to feed small haynets on a frequent basis rather than over facing the horse with one large one.
• Milk thistle: Anecdotal evidence suggests that milk thistle maybe beneficial and is increasingly being recommended.
• Cider vinegar: This maybe effective at decreasing blood ammonia, feed about 240ml to a 450kg horse (Mair, 2000)
• Other Vitamins: Additional B complex vitamins including folic acid and vitamin K should be supplemented or administered, since, while the healthy liver usually processes these vitamins, the unhealthy liver may do less successfully. Zinc supplementation may also help, as it is involved with the processing of amino acid breakdown products and deficiencies have been noted in humans with liver disease-associated mental abnormalities. Any additional supplementation of extra vitamins or minerals should not be done without seeking advice from your vet first. Vitamins such as A, D and K are stored in the liver and could become toxic. Excess vitamin D can lead to renal failure and excess vitamin K may cause haemolytic anemia.

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If you would like any further information, please feel free to contact our nutritional team on 01622 718487 or email info@saracenhorsefeeds.co.uk