LINDELL BEACH, B.C. — U.S. Department of Agriculture researchers are attempting to better understand the microbes that thrive in cattle’s gastrointestinal tracts.
They are particularly interested in which microbes live in cattle manure, how they thrive and what is the good, the bad and the ugly about these bacterial communities.
“The microbial community studies are still at a fairly early stage but they reinforce the idea that bacteria are a normal and natural part of agro-ecosystems,” said Lisa Durso, a research microbiologist with the USDA’s Agricultural Research Service in Lincoln, Nebraska.
Read Also
New MLA Tara Sawyer appointed to Alberta Next Panel
Former Grain Growers of Canada chair Tara Sawyer was elected to the Alberta legislature for the governing United Conservative Party in a byelection June 23.
“Some are bad, but many are harmless, or even potentially helpful. As we understand more about how the different bacteria interact, we hope to provide new solutions to food safety, animal health and environmental quality issues.”
It was once thought that all cattle had the same bacteria in their gastrointestinal tract, but the study is showing that each animal can have a uniquely different profile.
The research team studied the manure from six beef cows to identify the basic bacterial groups. All the animals were cross-bred MARClll beef heifers, which is a composite of one-quarter Hereford, one-quarter Angus, one-quarter Pinzgauer and one-quarter Red Poll.
They were all six to eight months old, 214 to 241 kilograms, housed in the same feedlot pen for two months before fecal collection and fed the same typical feedlot beef production growing rations of 61.6 percent corn silage (41.3 percent dry matter), 15.2 percent alfalfa hay, 20.9 percent corn and 2.3 percent liquid supplement.
The researchers used a new method called pyrosequencing to rapidly analyze DNA markers and give each bacterium an identification tag.
However, they were surprised by the diversity of what they found.
“All six animals were the same breed, age, and gender, and they had also been born and raised at the same facility, were housed together for months in the same pen, exposed to identical management and fed identical diets,” said Durso.
“These are all factors that are usually used to explain why there might be differences, but even when all these factors were the same, we still saw differences between the animals.”
Each animal had its own unique profile of bacteria, but as a unit the heifers represented a larger group of bacteria.
Durso’s study identified a core set of bovine gastrointestinal bacterial groups common to both beef and dairy cattle.
She determined that prevotella was the most common bacterial group representing 24 percent of the DNA sequences she analyzed.
“Microbes and manure are a classic combination,” she said.
“It is natural for all mammals and other animals to have lots of different kinds of microbes in their gastrointestinal tracts. While the specific kinds of bacteria change over time, the general number of bacteria in manure tends to stay about the same. If one kind of microbe grows less, there is always a competitor that will take its place.”
Durso said food safety used to focus on the animal, especially as it related to the dangerous E. coli O157:H7.
However, researchers are now focusing on bacteria and how they interact with all the elements in the life system.
E. coli bacteria live in two environments during their life cycle: the cow’s gut, where it is dark, warm and nutrient rich, and feces, where they struggle to live in an open environment with few nutrients to keep them alive.
Most manure microbes die but some survive to re-colonize a new host and continue the cycle.
“In order to develop strategic long-term control measures that work, we need to understand how the bad bacteria interact with all of the other bacteria in both the animal and the environment,” she said.
“The diversity of work we did was a kind of microbial reconnaissance that will help us identify which bacteria are commonly associated with the bad E. coli, and which bacteria might be natural competitors. When you are fighting an enemy, it makes sense to attack where the enemy is weakest. For the bad E. coli, our research is showing that that is in the environment.”
The study also looked at how livestock diets affected the movement of microbes in fields treated with manure.
Rsearchers focused exclusively on surface water and discovered that nutrients move differently in runoff than do bacteria and viruses.
In a separate study, Durso worked with ARS agricultural engineer John Gilley and his team to find out whether cattle diets affected mi-crobes when manure was spread on fields.
They studied manure from both livestock that had been fed corn and feed that contained 40 percent wet distillers grain. The two manures were applied to conventionally tilled and no till fields, and simulated rain events with a sprinkler system created runoff samples.
“While the majority of manure-borne microbes quickly die out in the environment, a small proportion can survive for extended periods of time,” she said.Â
“For example, we have cultured the bad E. coli from soil at a fairground 11 months after the animals were removed. Since children and others can get sick from as few as 10 of the bad E. coli cells, it remains important to use responsible manure management procedures to ensure safe drinking water.”
The researchers collected soil cores at the field site to track the movement of fecal bacteria, pathogens, and antibiotic resistant bacteria to evaluate the potential for ground water contamination.
They found no evidence that the bacteria were being transported through the soil into the ground water after five years of feedlot runoff application to this system.
Bacteria remained on the surface after the contaminated water had soaked into the ground, and eventually died. This held true regardless of whether the cattle were fed conventional corn or distillers grains.
“Despite the fact that cattle manure from animals fed distillers grains has different physical, nutrient and microbial qualities compared to manure from animals fed traditional corn finishing diets, sometimes including greater concentrations of pathogenic bacteria like E. coli O157:H7, we found no differences in how bacteria are transported in runoff,” Durso said.
“There is no additional concern over the microbiological quality of surface and ground waters in agricultural watersheds when distillers grains are fed to animals instead of corn.”
Meanwhile, studies continue to track a full census of bacteria in cattle manure to get a complete look at the diversity of microbes and their potential for harm.
“As far as diversity goes, we don’t know,” said Durso. “The tools that allow us to take a census of all the bacteria in manure have only recently been developed. We have a general idea of what the main microbes are, but researchers are only now starting to look at cataloging and tracking all of the bacteria.”
