Five of the eight B vitamins are required as coenzymes in the complex series of steps to convert propionate to glucose in the liver of the goat. For the average dairy owner and breeder to understand what this means and how it can relate to the health and wealth of his or her dairy goat herd, is important and requires delving into some background information as well as figuring out how to apply it to current feed and management systems.
Some time ago, when vitamins were first discovered, it was thought that there was only one B vitamin. Since then it has been established that there are eight, and although they are still classified as a B vitamin, they are very different from each other in structure and function. The eight recognized B vitamins are: B1 (thiamin); B2 (riboflavin); B3 (niacin); B5 (pantothenic acid); B6 (pyridoxine); B7 (biotin, sometimes called vitamin H); B9 (folic acid); and B12 (cobalamin).
Each B vitamin acts as a coenzyme. A coenzyme combines with another substance to form an enzyme. An enzyme is a type of protein produced by living cells that activates chemical reactions. In one way or another, B vitamins play essential roles in hundreds of these biochemical processes. B vitamins often work together in some reactions and in some cases one B vitamin is required to make another B vitamin available to the cell.
Required only in tiny amounts, B vitamins are involved in metabolic processes. Metabolism is defined as the creation of energy when one chemical is changed (broken down) into another. When protein, carbohydrates or fats are metabolized by enzymes, the result is a release of energy.
The interaction of B vitamins is well demonstrated in an important process that occurs in our goats and all other ruminants. Rumen bacteria produce volatile fatty acids (VFA’s) as by-products of the fermentation of plant cellulose, starches and sugars. One of these VFA’s, called propionate, is converted to glucose in the goat’s liver by enzymes. This is the goat’s only source of glucose. Five of the eight B vitamins play a role, as a coenzyme, in the chain of events where propionate is converted (metabolized) to glucose. Since glucose is included as part of the lactose molecule in the mammary cells, all five of these B vitamins are also essential to the production of milk.
B vitamins are called water soluble vitamins since they can be dissolved in water, but not in fat. It is also accepted that B vitamins, with the exception of B12 and folic acid, are not stored in the body for very long, just weeks in most cases and rarely more than a month. This is compared to vitamins A, D, E and K which are fat soluble vitamins. These vitamins are stored for long periods in the fat of the body which means that overdoses of these vitamins can result in a toxic buildup. Excess B vitamins that are not needed by the body are excreted in the urine. Vitamin C is also a water soluble vitamin.
The specialized bacteria that live only in the rumen synthesize (create) all eight B vitamins, as well as vitamin K, inside their cells. They in turn supply these vitamins to other rumen microbes and finally to the goat. Rumen bacteria have their own requirements for some of the B vitamins. Nearly all of the species require biotin (B7) for their own growth and individual species have requirements for one or more of the other B vitamins.
The goat obtains B vitamins when the rumen bacteria are passed to the abomasum (the fourth and true stomach) along with digested feed. Ruminants are unique in that they produce an enzyme which digests bacteria releasing their B vitamin store.
In the rumen, hundreds to thousands times more B vitamins are found inside the bacterial cells than in the free fluid. The wall of the rumen absorbs only a minimal amount of some B vitamins and in normal conditions is completely impermeable to others such as thiamin. B vitamins found in the feed or supplied as a supplement are either used by the microbes or changed by them into a different form, or may be absorbed across the rumen membrane. There is little information on just how much of the dietary B vitamins are degraded in the rumen or manage to be available to the ruminant further on in the intestine.
In studies where the entire rumen has been completely emptied, there is some indication that all B vitamins are absorbed through the rumen wall. And, when large quantities of B vitamins are introduced to the rumen most of them, including thiamin, do appear to be absorbed across the rumen, although the process is slow. However, according to most research, normally in well-fed ruminants few B vitamins are absorbed across the rumen membrane.
Large, single-cell rumen protozoa have a requirement for many B vitamins and do not make their own. They probably get most of what they require when they eat bacteria, which they enjoy in large numbers, but may use up some of those vitamins free in rumen fluid. This could account for some of the ruminal loss of supplemented vitamins. It is known that in normal conditions rumen protozoa use biotin that is available in the diet and seem to have some negative effect on bacterial use or synthesis of biotin under certain conditions.
In order to understand the fate of B vitamins either synthesized by bacteria, present in feed or supplemented by keepers, researchers have placed sophisticated sampling tubes in the duodenum, (the pouch located between the fourth stomach and the intestines) to sample the contents and look for levels of B vitamins that enter the intestines to be absorbed. The results seem to pose more questions than they answer. Depending on the study, either all of the B vitamins that exist free in the rumen disappear before they reach the duodenum, or some, and not always the same ones, do and some do not. The explanations are as varied as the results. Some vitamins may pass through in different, yet still bioavailable forms or attached to other molecules. Almost all researchers state that they do not completely understand whether B vitamins are absorbed in the rumen, used by the rumen microbes, destroyed or degraded by the rumen microbes, or possibly absorbed in the other stomachs or in the duodenum before they reach the sampling apparatus. The most consistent thing known about the fate of B vitamins in the rumen is that the available data is quite inconsistent.
Attempting to study the vitamin requirements of rumen bacteria or the type of B vitamin that each synthesize is a challenge. Rumen bacteria do not like living in laboratory conditions, much preferring the specific requirement of the rumen environment and company of other species which may provide them with necessities that scientists cannot duplicate. They resist being studied as an individual. The B vitamin requirements of some rumen bacteria are known, and it is known that other bacteria produce B vitamins but which species produce or use what is still largely a mystery.
It has been accepted that ruminants do not require B vitamin supplements since the bacteria supply all that they need. However, some new studies have shown that supplementation of some of the B vitamins have positive effects on hoof health, milk production, as well as other health benefits in ruminants.
Niacin has been extensively studied because supplementation in pregnant dairy cows has shown to decrease the incidence of ketosis. Even though niacin has been determined to completely disappear in the rumen, suggesting that the microbes destroy it when supplemented, it seems to wind up getting into the system to help where needed.
Biotin is another B vitamin that has been supplemented with positive results. Biotin is important in helping to build the structure of the hoof wall. Numerous studies have shown that supplementing biotin in the feed of cows improves the health of the hoof wall and decreases the occurrence of several common hoof problems especially those seen in wet conditions. At the same time it was noticed that there was also a positive effect on milk production. In a significant number of trials the amount of milk produced by lactating dairy cows increased when supplemented with biotin. In some experiments there was also an increase in the amount of biotin present in the milk. There also appeared to be a positive effect on conception rates in some cows.
It is suspected that biotin may not be increasing milk production, but is helping to bring production up to what would be a normal level if the cow were not deficient in biotin. Modern dairy cows have been bred to produce more milk than nature intended. The rumen bacteria may not be able to keep up with the high demand of heavy lactating dairy cows. Biotin is a coenzyme required in activating four different enzymes involved in milk production, and it is essential for converting propionate into glucose. It is possible that if a lactating ruminant, such as a dairy goat, is slightly deficient in biotin this could mean that some of these important reactions may not be working efficiently. Adding biotin to the diet would then bring milk production up to full potential. This idea is supported by the fact that biotin supplements help when given up to a certain amount. Supplementing beyond that limit ceases to have a positive effect on production.
Since biotin supplementation clearly improves the health of the hoof this may add to the positive effect on milk production and conception rates. Cows (and goats) that can move around more comfortably produce more milk and are more efficient breeders.
With two exceptions, deficiencies of B vitamins are rare in ruminants. Thiamin, or vitamin B1, acts as a coenzyme in producing a neurotransmitter molecule which is critical to proper functioning of the nervous system. A deficiency of thiamin causes the disease seen in goats called polioencephalomalacia (PEM) or what is commonly called goat polio. If thiamin levels are low, this neurotransmitter cannot be formed and communication between nerves is interrupted. The result is a goat that shows signs of excitability, tremors, muscle spasms and convulsions.
The reason for this deficiency in ruminants is thought to happen due to the presence of an enzyme called thiaminase which destroys or alters thiamin. It is known that the production of thiaminase is related to rumen bacteria, but it is not known exactly under what condition or which species produces thiaminase. It is suspected that diets high in concentrates which causes a more acidic environment in the rumen may either promote the growth of thiaminase-producing species or in some way increases the activity of the enzyme. Another possibility is that for some reason one or more species of rumen bacteria may produce a thiamin “look-a-like” molecule which competes for the uptake of normal thiamin. There is also evidence that high levels of sulfur in the diet produces PEM in beef cattle. Sulfur in the rumen produces hydrogen sulfide gas which is toxic to the rumen bacteria. In addition, some plant species contain thiaminase which may cause a thiamin deficiency if ingested.
Thiamin is not stored in the body and is quickly depleted under high energy requirements. It is one B vitamin which must be continuously supplied. Therefore, if conditions in the rumen cause a destruction of thiamin the goat rapidly becomes deficient. When a ruminant develops PEM, any thiamin given orally will be degraded by the presence or high activity of thiaminase in the rumen. To correct a thiamine deficiency, B1 must, therefore, be given as an injection.
B12 or cobalamin is the largest B vitamin molecule and has the most complex structure of all vitamins. Unlike other B vitamins which can be synthesized in plants, it is only synthesized by bacteria and they require an atom of cobalt in order to make a molecule of B12. Along with assisting in the metabolism of fats, carbohydrates, and proteins, B12 has the very important role in helping to produce all the red blood cells in the body. It also helps maintain the protective sheaths around nerves and to repair DNA. B12 works with folic acid in the production of an essential amino acid called methionine. In order for folic acid to be used by cells it has to be altered by B12. A deficiency of B12 therefore, results in a deficiency of available folic acid.
Rumen bacteria use B12 during the fermentation process of forming propionate. B12 is used in the liver of the goat in the chain of chemical reactions which convert propionate to glucose. Obviously, B12 is an important vitamin, so fortunately it is very potent. In most animals only a small amount in the diet is required. In addition, unlike other B vitamins, B12 can be stored in the liver for a long period of time. Ruminants, however, have a higher requirement for B12 than monogastric animals because the rumen microbes produce a large amount of propionate which requires B12 to convert it into usable molecules. Propionate can build up in the blood stream if there is a deficiency of B12.
Several factors can lead to a B12 deficiency. Since each molecule of B12 requires one atom of cobalt, a diet deficient in cobalt results in a B12 deficiency since the rumen bacteria cannot synthesize it. Diets high in concentrates lead to a high level of propionate production and therefore a high demand for B12. These diets also promote the synthesis of molecules that are similar to B12 but are not beneficial. Therefore, a high concentrate diet causes a higher demand for B12 but at the same time has a negative influence on the amount produced by rumen bacteria.
Severe parasite infections can damage the lining of the intestinal wall, reducing the amount of B12 that is absorbed. At the same time, chronic bleeding from the actions of these parasites causes an anemia which requires B12 to help restore lost red blood cells.
Symptoms of B12 deficiency include depressed appetite, and poor growth in young ruminants. B12 supplied in the feed is not well absorbed through the wall of the rumen and most will be used by the microbes since they have a high requirement. B12 is most useful as an injected supplement when required until the underlying cause of deficiency is corrected.
There are many ongoing studies related to understanding the role rumen microbes play in supplying our goats with their necessary B vitamins. Current focus is on producing B vitamin supplements that are ruminally protected which may help improve the overall health and productivity of goats, cows, sheep and other ruminants.
Karin Christensen has been a scientific illustrator for over 25 years. She recently developed a series of animations on the unique biology of the goat which has proven to be very popular learning tool for people of all ages and levels. She has kept a small herd of dual-purpose Nubian goats for 10 years. For more information: www.imagecyte.com.