SPECIAL REPORT: The microbiome: Knowns, assumptions, and possibilities
From the 2024 Kemin Intestinal Health Symposium
By Kristin Bakker
Dr. Todd Callaway took a deep dive into the microbial world to share some of the take-aways he’s gleaned from the last decade or so of research on the microbiome.
During the 2024 Kemin Intestinal Health Symposium, Callaway, associate professor in ruminant nutrition and gastrointestinal microbiology in the University of Georgia department of animal and dairy science, went through some of what researchers know and what they think they know about the microbiome and how the data can influence production-related challenges in livestock operations.
He said a lot of the questions being asked in microbiome research aren’t necessarily of high importance to the industry because researchers just don’t know which questions matter most. No one knows for sure yet what’s going on in the animal.
What we know or think we know
“We still don’t know what we don’t know. We always said the rumen and the gut is like a black box. Well, it still is. We’ve got a really good flashlight, but we still don’t know what’s going on in there,” Callaway said.
He referred to the core microbiome and questioned how much it matters in research. Every species has a microbiome, yet feed efficiency, growth rate and other factors can vary a lot from animal to animal – one important area where not enough is known yet.
It’s known that the microbial population is important to energy capture. A 2005 study by Ley et al. showed that germ-free mice could consume 30% more calories but remained thinner than mice with a microbial population. When the germ-free mice received a fecal transplant of microbes from the fatter mice, they gained weight, even when put on calorie-restricted diet.
“This shows the fact that we could change the microbial physiology through changing the microbial population or adding one,” Callaway explained, noting the study was the first to show the ability to adapt animal physiology using microbes.
In the 20 years since, there has been a lot of research on the gut microbiome’s effect on the health of the host, including inflammation, autoimmune disorders, and role of the gut-brain axis in mental health in humans. “A lot of those are linked to the microbial population in your gut,” he said.
Leaky gut also is linked to immune function. Inflammation stimulates the immune system, which leads to non-growth energy expenditure – something livestock producers do not want.
In cattle, the focus has been on how to reduce unnecessary energy expenditure so the animal has better feed efficiency/gain and less heat stress, for example. The tendency is to think there are several linked ecosystems within the animal and that the more diverse the microbial population, the better.
However, an Illinois study discovered that dairy cattle with excellent milk production and residual feed intake actually had less diversity in their microbial populations versus animals with a broader microbial population. It’s thought that they produced a narrower range of metabolites that were more beneficial to them, while the more diverse animals produced a broader profile of metabolites, some helpful and some the animal couldn’t use.
“So the animal itself is the compilation of all those ecosystems within it,” Callaway said, and the decisions producers make as to which animals to keep or cull will affect the ecosystems. Balance is important. When the ecosystem is out of balance, it’s called dysbiosis – like a “disturbance in the force” in the microbial population of the rumen or hindgut. That imbalance creates a ripple effect that impacts everything about the animal.
Research gaps
Can we make the microbiome better or worse? The ultimate goal in microbe studies is to improve animal performance. Callaway said the inflammatory response is crucial to reducing the impact on productivity and efficiency, as well as pathogen entry in animals.
But while it’s common knowledge that the use of antimicrobials and antibiotics increases feed efficiency, it’s not known why they work, even at a low level. It’s a big unknown that needs to be understood, according to Callaway. He said the microbes don’t matter so much as what they do – their function.
In addition, the role of metabolically important metabolites needs to be understood. Bifidobacteria, for example, is a beneficial probiotic because it stimulates and stabilizes the immune system, yet in a study of cattle the more efficient animals had a lower level of bifidobacteria. The opposite was true of Ruminococcus, with higher levels seen in the more efficient animals. It could be the result of the metabolically relevant metabolites the animal produces as an end product of fermentation. These are important questions to answer, he said.
Between the rumen and the hindgut, much less is known about the hindgut, and that may be where the biggest strides can be made in understanding the influence on efficiency to help producers.
The possibilities
What, then, can be done to prevent dysbiosis and improve feed efficiency? Callaway said one of the main ways is using feed additives like probiotics/prebiotics/postbiotics (“eubiotics”), organic acids, botanicals, ionophores. While there’s no silver bullet, they all can shift the host microbial population and, thus, the integrity of the gut.
There are many angles to explore to find out which changes in the microbiome affect what shows up in the live animal and which metabolites lead to better performance metrics.
Callaway said while it’s great to see all this information, we need to also know what the information is telling us. When looking at the microbiome, he said it’s not just what’s present at one point in time but what the end products are and what the long-term outcome is. He concluded that taking a eubiotic approach is promising, but it also will be important to know how diet and production management decisions play a role.
Watch the full presentation from Dr. Callaway and access all content from the 2024 Kemin Intestinal Health Symposium at kemin.com/symposium.
BONUS COVERAGEDr. Todd Callaway, a ruminant microbiologist with the University of Georgia, joins us to discuss the Microbial World: What Do We Know, What Do We Think, What Do We Hope? Dr. Callaway was part of the 2024 Kemin Intestinal Health Symposium.
View our interview
