Folacin

What it is
Yeast and liver extracts are known to have considerable nutritional benefits and have been used for centuries as tonics for sickly children and ailing animals. As analytical techniques improved in the 1920s and 1930s more and more compounds with nutritional importance were isolated from yeasts and liver. In 1935 an anti-anaemia factor for monkeys was found in both yeast and liver concentrates and was designated vitamin M. A few years later a water soluble anti-anaemia factor for chicks was extracted from liver and called vitamin Bc. Then, in 1940, a material encouraging the growth of bacteria was found in spinach, identified as an organic acid and named folic acid. In the mid-1940s all three factors were found to be the same substance and its chemical nature and configuration were determined. For a time it was known as vitamin B9. It is now known that there are several related compounds showing similar activity; these are generically grouped as folacin.

Chemically a folic acid molecule consists of three parts: a two-ring pteridine nucleus, glutamic acid and a para-aminobenzoic acid group (PABA). Additional molecules of glutamic acid may be joined by further peptide linkages but such compounds seem to be bi- ologically inactive. Conversely the inclusion of further hydrogen atoms or methyl groups produces folacin-active compounds.


What it does
Folacin compounds are very active in metabolism in transferring single-carbon groups from one compound to another. These may be simple methyl groups (-CH3), formic acid residues (-COOH) or similar one-carbon units which are carried loosely joined to nitrogen atoms in the folacin molecule. Folacin is directly involved in breaking-down and building-up specific amino acids such as threonine and histidine in the synthesis of purine and similar nitrogen-containing bases and the transport of methyl groups donated by methionine and choline.


If too much is given
Although there is some evidence of folic acid glutamates being stored in livers, kidneys and muscles, excesses of folic acid are excreted. There is no indication from any research that excessive supplies are harmful to horses or any other animal species.


Biosynthesis
The folic acid molecule contains para-aminobenzoic acid (PABA) which few micro-organisms are able to synthesise. However, given supplies of PABA, many micro-organisms can produce folacin. Such organisms are present in large numbers in the caeca of horses. There are considerable doubts regarding the effectiveness of caecal synthesis and the benefit to horses of any synthesised folacin.


How it is measured
The folacin contribution of a feed is usually determined by assaying biochemically the folic acid content in mg/kg. No International Unit for the biological activity of folacin has ever been defined. In addition to biochemical assays biological assessments can be made using chick- or rat-growth tests. Some of the folacin determined by biochemical assay of feed ingredients may be organically bound and biologically unavailable.


Assessment of status
The assay of folate levels in blood serum has been used effectively to investigate the folacin status of horses. The folate levels in livers may be better indicators of overall folacin status. It is also possible to determine folate status by measuring the amount of folate-dependent enzymes which should plateau when adequate folacin is available or the build-up of a metabolite which is normally broken down by a folate-dependent enzyme.


Antagonists
Several compounds interfere with the synthesis or metabolism of folacin. Sulphonamides seem to be accepted by many micro-organisms as alternatives to PABA. Thus simultaneously the growth of the bacteria and the biosynthesis of folic acid are inhibited. This is one of the principal modes of action of sulphonamides. There are also analogues of folic acid which contain amino groups instead of hydroxyl groups in the pteridine nucleus. These are not only non- effective as vitamins but actually inhibit the normal role of true folacin.


Relationships with other ingredients
There is a close relationship between folacin and vitamin B12 since both are involved in the transfer of one-carbon groups. It is found that a vitamin B12 deficiency frequently leads to a secondary folacin deficiency with a depletion of tissue folate levels.
This secondary loss of folacin can be prevented or alleviated by a supply of methionine. Folic acid metabolism can also be affected by a deficiency of iron.


Requirements and allowances
A certain amount of folacin is essential for metabolic activities. The actual quantity required depends on the availability of vitamin B12, iron, and methyl group donors such as choline and methionine. The daily requirement has to be absorbed from the digested feed through the intestine and some biologically-bound folacin is unavailable. It is therefore very difficult to determine a minimum requirement based on dietary supplies. There are also differences in the calculated requirements depending on criteria used in their determination. For example, normal blood cell production requires more folacin than the minimum needed for basic survival.

Most species, where research has been completed to determine folacin requirements, appear to need a minimum of 0.5mg folic acid per kg feed.

Horses kept in stables show considerably lower levels of serum folates than grazing horses. It has been found from research that intensive exercise over a 6-month period significantly decreased serum folate levels; it has also been discovered that the performance and endurance of horses with low plasma folates are somewhat poorer than those with ”normal” levels. Tests with oral folic acid supplements have shown a poor effi- ciency of absorption so comparatively large daily supplies are needed to increase plasma levels of stabled horses to levels similar to those found in grazing horses.

The obvious relationship between methionine and folacin has not yet been quantified but it would seem reasonable to assume that folic acid requirements are higher when methionine supplies are marginal.
The suggested levels of folacin supplementation of feeds for horses is shown above.


Contents of feed ingredients
It is sometimes difficult to know whether published figures for folacin contents refer to free or total folacin. Low concentrations of free folacin occur in feeds rich in energy such as the cereals while by-products lower in energy have higher contents. Animal protein meals and extracted oilseed cakes have the highest amounts. Folacin is present in all green-leafed vegetables including grass species.

    mg / kg   mg / day
Adult performance horses in training  
10
   100
Adult performance horses in light work   10   50
Ponies, hacks & hunters   5   15
Mares & stallions   5   20
Young horses 1-2 years   5   15
Foals & yearlings less than 1 year   10   10-30


Stability
Crystalline folic acid is fairly stable to air and heat but is degraded by light and particularly by ultra-violet radiation. It is affected by acids and alkalis. In spite of its classification as a water soluble vitamin it is only sparingly soluble in cold water but rather more soluble in hot water. It is unstable in the presence of water and remains potent for less than 24 hours in solution. Heat accelerates the rate of loss. Losses in pelleting are often about 20-30% and tend to increase with higher pelleting temperatures. At least 20% additional folic acid should be added to pelleted feeds to compensate for losses.