Thiamine-Vitamin B1 What it is Thiamine was the first vitamin to be studied in detail. It was found that the disease beriberi in people eating polished rice was prevented by adding rice bran back to the diet. The substance in rice bran with this effect was found to be an amine and the term vitamin was coined (vital-amine). Research has shown that thiamine, also called vitamin B1, is an essential dietary requirement for all animals. Aneurin was another name given to the vitamin. What it does Thiamine forms an essential part of several enzyme systems. These mainly involve the release of energy from absorbed or stored carbohydrates and fats. There are three main routes for releasing energy: glycolysis -- for example, the release of energy in working muscles; the citric acid cycle which occurs within cells; and the pentose phosphate cycle which takes place mainly in the liver, kidneys, adrenal cortex, mammary glands and blood erythrocytes. Enzymes are responsible for each of the chemical changes. Thiamine pyrophosphate (TPP) is a coenzyme factor directly involved with each energy-releasing process. It also seems to have a direct role in the activity of the nervous system, stimulating peripheral nerves. Increasing the thiamine supply above the basic minimum nutritional requirement can have an apparent calming effect on an excitable horse. If too much is given Horses have been fed extremely large amounts of thiamine without any apparent harmful effect. Thiamine is soluble and easily destroyed in the liver and kidneys so any amounts extra to the animal’s needs are rapidly excreted. Additional thiamine may have a tranquillising effect but gross excesses increase the pulse rate. Biosynthesis Most plants and unicellular organisms, such as bacteria, are able to manufacture and store thiamine. In particular, the micro-organisms found in the caeca of horses synthesise thiamine as part of their normal metabolic activities. Recent research suggests that horses may absorb about a quarter of the thiamine liberated in the caeca but this is unlikely to provide enough to meet their metabolic requirements. How it is measured Thiamine is used chiefly in the form of its chloride-hydrochloride salt (usually called thiamine hydrochloride). The activity of vitamin B1 preparations is usually expressed in mg thiamine hydrochloride. The mononitrate is also used and for most practical purposes it has a similar vitamin value to the hydrochloride. Pure thiamine is 78.7% of the hydrochloride or 81.1% of the mononitrate. Some older documents refer to an International Unit. This is not now in use but was the activity of 3mg of thiamine hydrochloride. Assessment of status The thiamine contents of blood and urine can be determined by assay. In deficiency situations the level in blood drops by 15-20% but fluctuations due to food intake can be greater so no conclusions can be reached. Measurements of the excretion of thiamine in the urine provide information on uptake but give no reliable indication of status. The best method of assessing status is to measure the amount of a thiamine-dependent enzyme. Transketolase is the best indicator and can be measured in International Units per litre of blood. It can also be determined indirectly by measuring the reactivation effect which compares the enzyme action on a carbohydrate with and without additional TPP. The comparison is expressed as a percentage and is positive in thiamine deficiency. 15-24% is a mild deficiency; over 25% is a pronounced deficiency. Antagonists Many substances have anti-thiamine activity. These may break down thiamine (the thiaminases) or interfere with its activity as a vitamin. Thiaminases are found widely in fish, ferns (including bracken) and micro-organisms such as bacteria and moulds. Kale, beet and field peas also contain thiaminases. Interfering substances may block absorption from the intestine or may be structurally similar and displace TPP from important metabolic reactions. Amprolium, a coccidiostat added to poultry feeds, interferes with thiamine phosphorylation and membrane transport. So if horses are fed poultry feed or feeds containing significant amounts of any of these antagonists there can be problems of induced thiamine deficiency. Requirements and allowances It is very difficult to determine a horse’s real thiamine requirement because of the uncertainty surrounding the value of caecal synthesis. Logically, active horses mobilising energy at a rapid rate need more thiamine than resting horses. Very young, growing horses need 500mg thiamine per day for every kg liveweight whereas non-active adult horses need rather less. Lactating mares require about 250 mg/day/kg liveweight. Thiamine-deficient horses should be given ten times their normal allowances by injection. This needs to be repeated every two to four days since excess thiamine is excreted via the urine and not stored. The needs for thiamine change if the horse is in a cold or hot environment. The neutral temperature range is 18--25 ° C; outside this range the horse has to use additional energy to keep warm or keep cool. If the temperature drops below this zone by, say 8° (to 10° C) the need for thiamine increases by as much as 20%, but if the temperature rises by, say 7° (to 32° C) the thiamine requirement decreases by 20%. Parasitic infestations can also increase thiamine requirements since both host and parasites compete for the thiamine in the food. Horse feeds should be supplemented with 8 mg thiamine per kg so that active performance horses receive about 80 mg/day and resting horses about 50 mg/day. Mares and stallions need 30-35 mg/day, young horses about 25 mg/day and foals and very young horses 8 -- 25 mg/day. The other ingredients of the diet should supply the remainder of the allowances. Contents of feed ingredients Most vegetable products contain some thiamine. It is often concentrated in the outer layers of seeds, seed germ and growing areas of roots, leaves and shoots. Fermentation products are good sources. Stability Thiamine is affected by hot, humid conditions. The extent of breakdown increases as the storage temperature increases above 20 ° C, particularly if there is free moisture in the air or in the feed. Destruction is further accelerated by high pH (over 6). There are some losses during pelleting and greater losses during extrusion. Pelleted feed should be supplemented with an additional 40% thiamine as the hydrochloride or mononitrate to allow for production and storage losses. Livestock conditions suggesting further needs Poor growth and performance may result from marginal supplies of any vitamin.