Salmonella is one of the leading causes of foodborne illnesses in the United States, according to the Centers for Disease Control and Prevention, and can spread to people from a variety of foods, including beef. Understanding how and why cattle become infected with Salmonella is an important part of fighting this major public health concern.
Researchers at the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) are addressing this problem from a new angle by studying how diet and feeding schedule impact Salmonella infections in cattle.
Their recent study, published in the American Society for Microbiology’s Microbiology Spectrum journal, found that high-starch diets can potentially lower Salmonella prevalence in cattle, especially within the lymph nodes — organs that are often embedded in fat trims included in ground beef products.
“Lymph nodes may be present in fat trimmings that are used to balance lean-to-fat ratios in ground beef products,” said Yesica Botero, a fourth-year biomedical sciences Ph.D. student. “This is a food safety concern because Salmonella can hide inside lymph nodes, where surface cleaning or treatments do not reach. As a result, it can still be present in ground beef.”
Feedyard cattle are typically fed a high-energy, grain-based diet designed to promote rapid growth and efficient weight gain.
Understanding the role that a high-starch diet potentially plays in reducing Salmonella prevalence could have major impacts on the beef cattle industry, providing ranchers with new options for controlling the spread of bacteria within their herds.
Taking A New Approach
The Texas A&M project was designed to study feedlot cattle that Dr. Kendall Samuelson, from West Texas A&M University, was examining in a separate project to see whether high-starch diets and feeding schedules impact liver abscess formation.
“We aimed to understand the factors that contribute to the presence and distribution of salmonella in feedlot cattle,” said Dr. Gizem Levent, a VMBS assistant professor in the Department of Veterinary Integrative Biosciences. “There aren’t many studies focusing on understanding how diet and management changes impact Salmonella.”
Botero and Levent took samples of feces, hides, lymph nodes and soil from Samuelson’s cattle pens over a period of more than seven months. They found that while there was little difference in Salmonella populations between cattle with scheduled versus erratic feedings, the level of starch in the diet made a notable impact.
“We saw a reduction in Salmonella, especially in the lymph nodes, when cattle were fed a high-starch diet,” Botero said. “High-starch diets typically cause a lower pH in the rumen, which may be what reduces Salmonella prevalence in the gastrointestinal tract and, subsequently, in lymph nodes.
“Findings from Dr. Samuelson’s original study suggested that high-starch diets may also correlate with a higher incidence of liver abscesses,” she said. “This is something we would like to explore further in upcoming studies by testing different starch concentrations in the diet to find one that does not harm cattle health — such as by increasing the risk of liver abscesses — but still helps lower Salmonella levels.”
Continuing The Investigation
In addition to studying how different levels of starch impact liver abscesses and Salmonella, Levent and Botero are planning to dive even deeper into the data to study the specific serotypes, or genetic profiles of Salmonella, observed in their samples.
“We want to do a follow-up study with more in-depth analysis of the dynamics of the Salmonella population,” Botero said. “By looking at the genetic profiles, we can better understand which serotypes are present, how they might respond to antibiotics, and whether they carry genes that make them more likely to survive or spread in the environment.”
Fortunately, what they have seen so far from the feedlot samples does not indicate a high presence of Salmonella or serotypes resistant to antibiotics.
“The overall Salmonella population found was not resistant to antibiotics of public health concern, which is good news for public health,” Levent said. “But we will definitely keep screening for resistance so that we can better understand what makes resistant populations exist in the environment.”
