The Rumen And The Hoof
By Karin Christensen
Certain conditions in the rumen can lead to laminitis (founder) of the hoof due to the overgrowth of some species of rumen bacteria.
A balanced population of bacteria in the rumen consists of about a dozen or more different species. Fibrobacter succinogens, Ruminococcus albus and R. flavefaciens are the most common species of rumen bacteria. Called cellulolytics they specialize in the digestion of cellulose. Cellulose, the major component of plants, is made up of long strings of glucose held together by strong bonds. These bacteria have enzymes, which break up the cellulose into individual glucose molecules which they use for their own functions in a process called fermentation. This process produces byproducts called volatile fatty acids (VFAs), which are waste to the bacteria but once absorbed across the rumen membrane are essential for metabolic processes by the goat. The rumen also has a population of single cell protozoans and even a unique fungi, but it's the bacteria that play the major role in digestion of forage material and in feeding the goat.
Other rumen bacterial species, such as Streptococcus bovis, specializing in the digestion of the starches or sugars found in the seeds of plants, are normally found in lower numbers in the rumen since ruminants are not naturally starch eaters. When a ruminant is fed an overabundance of grain which contain high amounts of starch and sugar, these bacteria will overgrow on the additional food source. Starch digesting bacteria typically produce lactic acid as a byproduct of fermentation. Lactic acid is not a VFA that is absorbed across the rumen membrane.
Yet other species of rumen bacteria which are also present in low numbers are able to convert lactic acid into usable VFAs. It takes some time for a population of these bacteria to build up so the change to grain needs to be gradual. Although, even once these bacteria grow in number, a diet that includes starch will usually result in a chronic, mild acidosis.
If the grain is fed in sudden high amounts excess lactic acid will rapidly accumulate causing severe acidosis. Cellulolytic bacteria are sensitive to acidic conditions which inhibits their ability to digest cellulose. They will not die, at least not right away, but are unable to function. The starch-digesting bacteria, which are not sensitive to a slight acidic pH, continue to digest starches making things worse.
The inside surface of the rumen is not protected by mucus like the lining of our stomachs or the goat's fourth stomach. Acidic conditions in the rumen, even briefly, will cause inflammation, ulceration and scarring of the lining. Worse, these conditions will promote the growth of bacteria called Fusobacterium necrophorum, which can utilize lactic acid. This bacterium infects the ulcers on the rumen membrane and if it can make its way through the ulcer into the blood stream it ends up in the liver causing abscesses. This is a common problem in feedlot cattle that are fed high amounts of grain and one reason why antibiotics are commonly used in these operations.
F. necrophorum also produces endotoxins and if the conditions in the rumen remain acidic for long periods the cells lining the rumen begin to produce an enzyme that causes tissue degradation. If these endotoxins and enzymes get into the blood stream they will cause the hoof tissue to become inflamed and in some cases the hoof wall will fall off.
Lactic acid producing bacteria can also secrete polysaccharides, which produces foam causing frothy or feedlot bloat. The foam traps the gas bubbles, which can't be released. If the gas pressure gets too high the lungs are compressed, suffocating the goat.
When excess grain is fed, undigested starch passes through the rumen and eventually winds up in the intestine. Since ruminants are not starch eaters they do not have the necessary enzyme in their intestines to break down the starch molecules into simple sugars that can be absorbed across the intestinal membrane. Instead, a bacteria named Clostridium perfringens that normally lives in the intestine in small numbers readily digests the excess starch. C. perfringens will rapidly overgrow and produce toxins that cause the disease we know as enterotoxemia.
It has become a popular misconception that many of the diseases we see in goats are related to the dying off of the population of microbes in the rumen. As a result a common recommendation is to use a probiotic product or yogurt to replenish the rumen bacteria or restart the rumen.
However, probiotic products contain mostly Lactobacillus species (lactic acid producing bacteria) and others that colonize the intestine. They do not contain any rumen microbes which can only survive in the unique environment of the rumen requiring strict conditions of pH, temperature and are anaerobic which means that oxygen will kill them. Researchers have a difficult time cultivating rumen bacteria in the laboratory even using sophisticated equipment, finding that the population quickly shifts from what's normal in the animal. Some species and all the protozoa can't handle life outside the rumen, dying in a short time.
Microbes are established in the rumen only by transfer from the mouth of one goat to another. A doe will clean her newborn kid's face and mouth and in the process inoculate it with the first few bacteria which quickly grow into a large colony by the time the kid is ready to eat forage. Some bacteria can survive for a very short time in airborne droplets of saliva which are transferred from goat to goat when they feed close together.
Fortunately, we rarely need to worry that the entire colony of microbes die off. Outside of starvation, the goat would need to be given high doses of oral antibiotics or have experienced serious long-term acidosis to kill off most of the microbes. Even then there would be a few species left that were able to survive the harsh conditions. But, the goat is healthiest when the rumen contains a large colony of diverse bacterial species. Therefore, if for some reason a goat needs an inoculation of rumen microbes, the old tried-and-true method of removing fresh cud from a healthy goat and immediately placing it in the mouth of the sick goat is about the only way.
As always, prevention is always the best course. Grain and sugars should be fed in low amounts and changes in feed should occur gradually over a period of a few weeks to allow the population of microbe species to adjust. Microbes and goats have been living in a symbiotic relationship since the beginning. They have it all worked out as long as we do not upset the balance.
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