Discover how adding essential oils to dairy calves’ diet could combat E. coli. New research from Stellenbosch University reveals intriguing findings.
Monensin is an antimicrobial substance frequently integrated into the diet of dairy calves. It is used to maintain gut health by warding off parasitic infection and also promote growth. However, concerns arise when the feeding of sub-therapeutic doses of monensin potentially boost the resistance of Escherichia coli (E. coli) in calves. This, in turn, could pose health risks to humans susceptible to these antibiotic-resistant strains.
Michelle Gouws, a recent Animal Science master’s graduate from Stellenbosch University (SU), offers a compelling argument. “Dairy farmers should consider adding a blend of essential oils to the diet of calves,” she recommends. Gouws’s research on this topic was recognized as one of the top 10 poster presentations at the European Symposium of the International Association for Food Protection held in Aberdeen, Scotland, from May 3-5, 2023.
Now undertaking her PhD in the Faculty of Agrisciences at SU, Gouws became curious about whether essential oil compounds could provide an effective alternative to the commonplace monensin in the diet of pre-weaned calves. Essential oils, as previous studies indicate, boast antimicrobial and immune-boosting properties, rendering them beneficial to the overall health of pre-weaned calves, poultry, pigs, and cattle.
“To prevent an increase in multidrug-resistant E. coli on farms, this study suggests that dairy farmers should avoid feeding calves monensin, but rather add essential oil compounds to calf diets,” she explained.
As part of her research, Gouws conducted field trials on two distinct farms in the Western Cape. She assessed the growth, overall health, and performance of calves fed a diet either of monensin or an essential oil mix (containing carvacrol, capsaicin, and cinnamaldehyde). The calves were randomly grouped into three treatments: a control group; a group fed with a liquid garlic extract diet and a solid feed fortified with essential oil compounds; and a group offered a diet containing monensin. She also evaluated the antibiotic susceptibility of E. coli and Salmonella isolated from the calf faeces.
According to Gouws, the results showed no noticeable differences in overall growth, health, and rumen development among the three groups. Yet, both monensin and the essential oil compounds influenced the level of antibiotic-resistant E. coli.
While there are clear advantages to both monensin-inclusive and essential oil diets, she warns of a concerning aspect of the former. “A diet containing monensin increased the resistance of E. coli to certain antibiotics,” she pointed out.
Gouws stresses the need for more research to fully explore the advantages of a diet rich in essential oil compounds under varying production conditions and parameters. She highlights the sobering reality that misuse and overuse of antibiotics in livestock farming are a significant problem. This could lead to the development of pathogens resistant to antibiotics critical to human health. Such antibiotic-resistant pathogens can be transmitted to the human population via contaminated soil, water, or food, inevitably reducing the effectiveness of certain antibiotics to treat human diseases.
“By reducing the risk of the development of antibiotic resistance in pathogens of livestock, we may ensure that antibiotics used for treatment of infection in humans remain effective,” she noted.
In highlighting the longevity of this issue, Gouws points out that monensin, along with various other feed additives, has been banned in the European Union due to their potential to increase antibiotic resistance in livestock. “As a result, the search for alternative, growth-promoting and disease-preventing feed additives for inclusion in calf diets has intensified,” she states.
Due to links between low concentrations of antibiotics usage and increased multidrug-resistant bacteria, she asserts that surveillance programmes for the overuse and misuse of antibiotics in major, industrial dairy operations are crucial. These programmes are vital as many antibiotics used in livestock are not strictly regulated and can easily be procured over the counter.
Gouws concludes by stating that collaboration and knowledge sharing among veterinarians, farmers, and the animal feed industry are instrumental in mitigating antibiotic use and preventing the emergence of antimicrobial resistance in livestock.
