???Monensin, an antimicrobial substance that can be used to kill or prevent the growth of microorganisms, is frequently added to the diet of dairy calves to prevent intestinal infection caused by parasites, and to improve calf growth. The feeding of sub-therapeutic doses of monensin, however, can increase the resistance of the disease-causing Escherichia coli (E. coli) bacteria in calves, which in return can have health implications for humans.
“Dairy farmers should consider adding a blend of essential oils to the diet of calves," says Michelle Gouws, who recently obtained her Master's degree in Animal Science at Stellenbosch 肆客足球 (SU). Her study was one of the top 10 poster presentations at the International Association for Food Protection's European Symposium held in Aberdeen, Scotland, from 3-5 May 2023.
Gouws, who is currently enrolled for a PhD in the Faculty of AgriSciences at SU, wanted to determine whether a blend of essential oil compounds could be an suitable replacement for the more conventional monensin in the diet of pre-weaned calves. She says previous studies have shown that essential oils have antimicrobial and immune-boosting properties, as well as overall health benefits for pre-weaned calves, poultry, pigs, and cattle.
As part of her study, Gouws conducted trials on two different farms in the Western Cape. She studied the growth, overall health, and performance of the calves to determine the benefits of a diet containing monensin or a blend of essential oil compounds (i.e. carvacrol, capsaicin, and cinnamaldehyde). The calves were randomly allocated to one of three treatment groups, i.e. a control group; one that was fed a liquid diet containing a garlic extract and a solid diet with a blend of essential oil compounds; and one that was fed a diet containing monensin. She also determined the antibiotic susceptibility for E. coli and Salmonella isolated from the faeces of the calves.
Gouws says she did not observe any difference in overall growth, health and rumen (one of the forestomach compartments) development between the three groups. She did, however, find that monensin and essential oil compounds had an impact on the level of antibiotic-resistant E. coli.
“Even though the growth and health benefits associated with either a diet containing monensin or a blend of essential oil compounds were similar, a diet containing monensin increased the resistance of E. coli to certain antibiotics.
“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."
Gouws does however, emphasise the need for further research to determine the benefits of a diet of essential oil compounds, with a different set of parameters and under different production conditions.
She says the misuse and overuse of antibiotics in livestock is cause for great concern, as this may result in pathogens that become resistant to medically important antibiotics. These pathogens can be transferred to humans through contaminated soil, water or food, and can easily result in reduced efficacy of antibiotics to be used in the treatment of certain diseases.
“By reducing the risk of the developemnt of antibiotic resistance in pathogens of livestock, we may ensure that antibiotics used for the treatment of infection in humans remain effective".
Gouws points out that monensin is one of various feed additives that have been banned in the European Union due to concerns about increased 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.
“Due to the link between the use of low concentrations of antibiotics and increased multidrug-resistant bacteria, surveillance programmes for the overuse and misuse of antibiotics in large, commercial dairy operations should be implemented."
According to Gouws, such surveillance programmes are needed because many antibiotics used in livestock diets, are not strictly regulated and can easily be bought over the counter.
She says that collaboration and sharing of knowledge between veterinarians, farmers, and the animal feed industry can help to decrease the use of antibiotics, and prevent the development of antimicrobial resistance in farm animals.
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