When a dog starts a new diet, the microbial community in its gut changes. The wall bacteria multiply to dominate the scene and the old guard flees in defeat. As the microbial species battle for control, their metabolic byproducts, many of which are critical to Fido’s overall health, also change.
The dynamic dance between nutrients, microbes, and their chemical products is well documented in dogs and other mammals, but until now scientists have only guessed at the timing of microbial transformation. A new study by zoological scientists at the University of Illinois documents that change occurs in less than a week.
“While I’m doing animal nutrition research, we’ve been debating how long we should feed a new diet before collecting samples when everything stabilizes,” says Kelly Swenson, professor of human nutrition at Kraft Heinz. Department of Animal Sciences and Division of Nutritional Sciences at University I and co-author of the new study. “No one has ever tested it definitively.”
It turns out that microbes stabilize very quickly. They start producing completely new chemicals within two days of the dogs transitioning to the new diet. And it only takes six days for the microbial communities to shift and stabilize.
“Metabolites change very quickly, within days. The bacteria respond by metabolizing and coping with the substrates given to them in the new diet. Then it takes a few more days to sort out the pecking order of the microbes, if you will,” says Swanson. . “Our data shows that everything stabilizes by day six, so animal nutrition researchers can confidently take a sample and find a stable microbiome for 10 days.”
Swanson’s team fed the dogs regular dry food for two weeks before abruptly switching to the new diet for an additional 14 days. Half of the dogs ate canned foods high in fat and protein, while the other half ate high-fiber flakes. At the same time, the researchers collected feces two days after the diet change and every four days thereafter. Because science requires repetition, the researchers did it all twice, the second time putting the dogs on the opposite experimental diet.
The team extracted from each stool sample microbial metabolites, those chemical products of microbial metabolism that can affect the overall health of the dog. They also identified the species of bacteria in the stool samples to show how the microbial community changed over time. Finally, they correlated metabolites with bacterial species, which had not been done before for most bacteria.
“Oftentimes we feed the diet and collect the feces, but there’s kind of a black box in terms of what’s going on in the gut. We know what some types of bacteria are metabolizing, but certainly a lot of it is unknown,” says Swanson. “Our correlations are a starting point for connecting some of the dots, but a more focused study is still needed.”
The main aim was to track changes in the micro-organisms over time, but the study also confirmed previous findings suggesting greater health benefits of a high-fibre diet compared to a high-fat, high-protein diet for dogs. These findings were not a surprise, but the fact that the two extremes of diet reached equilibrium in the same time period was unexpected. For both diets, the team found changes in metabolites on the second day and changes in the bacterial community on the sixth day.
Swanson says the generalities of the study may be applicable to other mammalian microbiome systems, especially those like pets and livestock that eat the same controlled diet every day. For example, the speed with which the gut microbiome responds and stabilizes after dietary changes may be universal. And although individual species and strains of bacteria may differ in dogs, humans, and other mammals, the metabolite/species correlation may be similar in different hosts.
Is there a takeaway for dog owners? Swenson says that although his study involved a very drastic change in diet, his results support the general recommendations for gradually transitioning to a new brand of dog food.
“People usually suggest transitioning pets to a new diet within seven days. Our research shows that the microbes can completely change in that time,” he says. “When you change your diet, the body has to adapt, but the microbes have to change too. If they’re not in a happy state, you end up with loose stools or flatulence. So it’s probably good to do it a little bit more at home gradually than in the laboratory.”
This research was conducted in partnership with NomNomNow, Inc., a direct-to-consumer manufacturer of fresh pet food and health products. Nom Nom has an extensive pet health and microbiome database, enabling them to participate in a variety of microbiome-focused research in the pet population.
“We are very excited about the results of this trial,” said Ryan Honaker, director of microbiology at Nom Nom. “Understanding the microbiome is central to our efforts to improve pet health, and this study brings us one step closer to discovering how the canine gut actually responds to a new diet.”