It’s no secret that bacteria have a bad rap. With constant marketing of hand gels, soaps, wipes and other personal antibacterial products, it’s not surprising that most of the non-scientific public fears bacteria. However, maintenance of the proper microbes in the intestinal tract allows animals to gain nutrients from their food that they cannot absorb from their own digestion. In fact, with over 1 billion bacteria in our intestine, the bacteria outnumber our own cells 10 to 1.

Bacteria present in dogs and humans are similar, which is not surprising given our similar predispositions for eating what is available at any given time. The cat’s microbiome is still being determined. The microbial community of any animal is a dynamic population.

We are what we eat, but are microbes also indicative of where we’ve been? In some ways, they are. Animals that are raised exclusively indoors have different bacteria present in their intestines than those raised with exposure to an outdoor environment (Mulder, 2009). Dogs that run outside frequently could have a different variety of bacteria present in their intestine than more sedentary indoor animals.

In the lab, the growth curve of bacteria may be easily manipulated by changing the media provided for nutrition. Simple sugars are used quickly, and when they are used up the bacteria dies. More complex prebiotic fibers may give the desired beneficial bacteria a prolonged growth curve. In the animal, this gives the commensal bacteria a survival advantage. Products that contain specific prebiotics that target the probiotic are known as synbiotics (Figure 1, p. 36).

Probiotics, which are live bacterial products, have become popular for their proposed benefits to humans. This popularity has now spread to our pets as well. There are many things to consider when deciding how to choose the bacterial species included in a supplement or petfood diet, such as:

  • Will the bacteria survive food processing and through the stomach of the animal so they reach the intestine?
  • Do the bacteria give a desired benefit to the animal?
  • Is the target dose of the live bacteria still known at the time of feeding?

When fed, live bacteria elicit a different immune response than when they are dead. In a 2009 study, Van Baarlen and colleagues investigated the differences in immune response when a probiotic strain of Lactobacillus was fed to mice when the culture was live and harvested when actively growing vs. a killed preparation of the same bacteria. They found that while the live bacteria stimulated intestinal cell proliferation, the dead bacteria stimulated the immune system of the mouse, causing an inflammatory response characterized by TNF cytokine excretion.

Similar results were found in a study conducted by Kemin Nutrisurance with the probiotic Subactil. When fed to mice at live doses from 10 million to 10 trillion bacteria/gram, the Bacillus organism did not elicit an inflammatory response, but a killed dose of the bacteria increased circulating levels of pro-inflammatory cytokines.

With only one layer of cells between the intestine’s microbial population and the rest of the body, it is important to have a friendly relationship with our intestinal bacteria. When searching for a probiotic to maintain that relationship for pets, there are many considerations to contemplate, including lifestyles and nutritional challenges.

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Intrigued? Read Dr. Cutler's entire article on probiotic considerations for petfood.