Probiotics and Pet Health

By Lark Burnham, Ph.D., Animal Nutrition

Microflora and the Gastrointestinal Tract

The gastrointestinal tract (GIT), which extends from the mouth to the rectum, contains approximately 400 different species of microorganisms, called endogenous microflora, and includes bacteria, yeasts, fungi and protozoa. These microflora are acquired at birth from the mother (during the birth process and through direct physical contact afterward), and later from the environment, and are necessary for the health and proper functioning of the GIT.

Beneficial or endogenous microflora play an intrinsic role in both digestion and immunology. They help degrade food, especially in sick animals when enzymes may not be secreted, convert waste material to energy, and are the first line of defense against infection. Digestion in mammals is a cooperative effort between enzymes secreted by the body and those secreted by endogenous microflora. Some animals do not generate the required enzymes, as in those with Exocrine Pancreatic Insufficiency (EPI), or Lactose Intolerance (LI). In these animals, the undigested material must then be degraded by microorganisms in the GIT.

Because conditions in the GIT are not normal for animals with digestive disorders such as EPI and LI, they can cause the proliferation of microorganisms that are usually found only in small numbers. If not controlled, these opportunistic pathogens can cause serious problems such as diarrhea and gas.

The endogenous microflora also play a key role in an animal's immunological response. Infections that enter through the GIT must first overpower the endogenous microflora. Under normal healthy conditions this happens only with a very large initial dose of infectious microorganisms; however, if the animal is stressed, a smaller number can successfully infiltrate the GIT.

Stress and the Gastrointestinal Tract

When a mammal experiences stress, changes in pH or the cessation of nutrient flow can occur, which can kill endogenous microorganisms. The resulting "gaps," or locations within the GIT that are stripped of these naturally protective microorganisms, are an open invitation to opportunistic pathogens. Pathogens continually pass through the GIT, but if the animal is healthy or the pathogen number is low, they will pass through without doing any real damage. Gaps in the protective barrier, however, allow pathogens opportunities to establish themselves. Pathogens can make animals sick by simply competing for available nutrients and starving the beneficial microorganisms, or, more seriously, through the production of toxins. Many forms of food poisoning involve bacterial toxins. Sometimes a very small amount of toxin can cause an animal to become very sick or even die, and this process can occur quite quickly.


The conventional treatment of infection is to use antibiotics, which are like nuclear bombs to bacteria - they kill both good and bad indiscriminately. That means along with the pathogens, many beneficial microorganisms may be killed as well, and sometimes the target microorganisms may even survive while beneficial ones are killed. The original antibiotics were actually derived from microorganisms by isolating various strains of beneficial bacteria. Beneficial microorganisms pack an assortment of biological weapons, both physical and chemical.

Unfortunately, microorganisms possess the capacity to evolve resistance, so antibiotics can become ineffective; pharmaceutical companies must continually search for new antibiotics. Probiotics are microorganisms used to combat other microorganisms, and can provide an alternative to antibiotics that rapidly become obsolete.

Probiotics, which are also known as direct-fed microbials, or DFM, are defined as live microbial feed supplements which beneficially affect the host animal by improving its microbial balance. Probiotic microorganisms, which include bacteria, yeasts, and fungi, are good competitors and can push back pathogens and allow the endogenous microorganisms to recover. They also stimulate the immune system so that the body can fight more effectively. Although probiotic microorganisms are confined to the GIT, they have wide-reaching effects and can help control infections not located in the GIT by activation of the immune system.

One way to think of probiotic microorganisms (which are generally not endogenous species unless isolated and developed for a particular species) is as armed placeholders. They fill gaps until the endogenous microflora, decimated by antibiotics or stress, can recover. Once they are back on their proverbial feet, they give the probiotics the boot. Probiotic microorganisms usually do not attach and become permanent residents.

Because the GIT microflora is so varied (bacteria, yeasts, fungi and protozoa), it may require different types of microorganisms to fill different gaps in the GIT ecology. Different species of all types are vulnerable in differing degree to stress and antibiotics. The best way to ensure that the greatest number of gaps are temporarily filled by probiotic microorganisms rather than opportunistic pathogens is to use a wide-spectrum probiotic, or one that contains the widest possible selection of different species in the required amounts. No one probiotic species is the best in all possible scenarios. All forms of Natur's Way Pet Probiotics contain similar microorganisms, just in varying amounts depending on need.

Numbers of viable probiotic microorganisms are crucial, both the amount of any one species (called colony-forming units, or CFU) and species of biologically different microorganisms. The numbers of beneficial microorganisms must be superior to the invading organisms, even after they have passed the stomach. Scientific literature recommends at least 100,000,000 CFU/g or greater for treating sick animals. The state of the animal and the intensity of the stress experienced dictate the concentration of the probiotic the animal should receive.

Probiotic microorganisms can be freeze-dried to retain full viability and potency until mixed with water, which happens naturally once ingested. Some strains of bacteria are able to go dormant if availability of nutrients or environmental conditions becomes unfavorable for growth. Powdered or granulated forms must be kept dry until fed to maintain full potency. Other conditions such as heat and sunlight can also kill probiotic microorganisms, even in the dry state. For the longest shelf life for any probiotic, keep tightly sealed and refrigerated. Dried forms may also be frozen once, but not repeatedly thawed and refrozen. Freezing can extend potency past the expiration date. Paste and liquid probiotics must be refrigerated, and cannot be frozen. They have a similar shelf life if kept sealed and refrigerated. Probiotics come in at least three different concentrations:

  1. Maintenance — should be fed daily for everyday stresses such as weather and occasionally being left alone. Usually supplied as a powder or granules.
  2. Intermediate — should also be fed daily for chronic stresses and many digestive problems. Usually supplied as a powder.
  3. Concentrated — can be fed one or more times daily for treatment of a sick animal until the animal is eating normally. Available in either paste or liquid.

Because maintenance probiotics help reestablish proper microbial balance in the GIT, it can take from 10 to 14 days to become fully active. The more concentrated forms start to work within just a few hours.

One common concern about probiotics is whether they survive past the stomach. One of the most effective probiotic microorganisms is Lactobacillus acidophilus, a lactic acid-producing bacteria that actually lives in the stomach. It prefers acid (the name means "acid lover") and will secrete enough acid on its own to maintain a pH uncomfortable for many opportunistic pathogens. Research has shown that L. acidophilus generates enough acid during nursing to postpone the secretion of hydrochloric acid in the young mammal.

Other probiotic microorganisms prefer the less acidic environs of the large intestine, and will successfully pass through the stomach and continue to the colon. There are always some probiotic microorganisms that succumb to the extreme conditions in the stomach, and that is why the initial dose needs to be as high as it does. This will ensure that the proper number of viable microorganisms reaches their target locations. Some probiotic products boast about special encapsulation or other methods that are purported to bypass the stomach. These elaborate marketing schemes are not necessary as long as the product delivers the recommended number of viable probiotic microorganisms.

Handling and storage of probiotics can greatly influence the actual numbers of viable microorganisms that are fed to your pet. If you buy off-the-shelf or from a distributor, do you really know what you are getting? That package may indeed have had the CFU of the various organisms listed on the label when it left the manufacturer, but that does not mean it has that many when you actually make the purchase. The most effective probiotics are the freshest ones, and the ones that have spent the least time away from the manufacturer.

Illness and the Gastrointestinal Tract

When an animal becomes ill, the GIT is shut down and energy and other nutrients are shunted to the immune system. Normally, there is only about a day's worth of ready energy stored in the muscles (as glycogen, or animal sugar), and when this runs out the metabolism must burn fat for energy. Depending on the severity of the illness, the animal may not have time to complete this time-consuming metabolic process. As soon as the GIT shuts down, the clock starts ticking, and if the immune system cannot defeat the infection before energy runs out, the animal will die.

Probiotic microorganisms can metabolize food left in the GIT after it shuts down. The energy derived from this metabolism, mainly volatile fatty acids (VFA) or short-chain fatty acids (SCFA), is readily absorbed by the lining of the digestive tract, thus buying the animal more time.

A serious complication of undigested food in the GIT after it shuts down is the arrival of highly fermentable nutrients in the large intestine. This happens when sugars and starches that would normally have been digested enzymatically are fermented in the large intestine. Pathogenic bacteria may proliferate and cause diarrhea, which in itself can be fatal.

There are some problems with antibiotics: they may or may not kill the initial invading microorganisms, and they can kill beneficial microorganisms, which leaves the host open for secondary infections. Probiotics are strongly recommended when also using antibiotics, and at twice the usual rate. Since antibiotics can kill probiotic microorganisms, the doses should be staggered to maximize the benefits. Probiotics can prevent secondary infections and may help the animal recover faster.

Any conditions that result in changes in nutrient flow or pH can affect endogenous microflora. Many of these microorganisms are attached to the walls of the GIT and depend on nutrients coming to them, and when they don't, or the pH in their niche changes even a tenth of a point, they can die. Diseases that affect non-GIT organs can impact nutrient flow and may exacerbate the initial condition. The digestive tract, the microflora, and the immune system are all intrinsically connected, and what hurts one will impact the others. Very few diseases are isolated in nature, and can have repercussions throughout the animal's body.

Probiotics should be selected based on the health and stress level of the animal, and they work well with any veterinary therapy. Both cats and dogs benefit from the regular use of probiotics.

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