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Avoid antibiotic resistance in calves fed waste milk

Contributed by Mike Opperman Published on 24 February 2022

Cows spend the vast majority of their lives eating forages and concentrates and turning those products into large volumes of high-quality milk. But it’s the first four to six weeks of their lives that impact their development and even productivity later in life.

Feeding whole milk or a milk replacer during the first few weeks of life is critically important to growth and development, as well as future productivity.



Whole milk fed to calves may be waste milk from cows treated with antibiotics. The source of the antibiotics can come from two different areas:

  • In colostrum or fresh cow milk: Colostrum and milk from cows treated with antibiotic dry cow therapies can contain antibiotic residues. While the increased use of selective dry cow therapies has lowered the use of antibiotics to treat or prevent mastitis in dry cows, many cows still freshen with antibiotic residue in their colostrum or transition milk.

  • From treated lactating cows: Antibiotics used later in lactation either as a way to treat clinical mastitis or to treat other health-related challenges.

There are two uses of waste milk, both of which can cause challenges due to the presence of antibiotic residues.

Persistent bacteria populations

One option is to just dump the waste milk down the drain. This usually ends up in a waste management system that eventually gets spread on crop fields along with the rest of the manure from the dairy. These residues don’t break down in soil, so they either have the potential to end up in the groundwater or be taken up by plants that eventually get fed back to the herd.

In addition, calves fed waste milk that contain antibiotic residues can also develop bacteria resistant to antibiotics. This poses a larger issue that impacts the long-term health and productivity of the animal.

So if you feed waste milk to calves that contains antibiotic residues, you risk the development of antibiotic-resistant bacteria and the associated health risks. If you don’t feed the waste milk, you probably pay a higher price for milk replacer while risking the introduction of antibiotic residues to the environment.


Supplement can reduce antibiotic resistance

One novel strategy has been developed to help reduce the development of antibiotic-resistant bacteria in calves fed waste milk containing antibiotic residues. This strategy involves feeding essential oils in whole milk.

A research study conducted at the University of Reading in England evaluated the potential of using essential oils to mitigate the risk of the development of antibiotic-resistant bacteria. Two similar groups of calves were fed waste milk from the university dairy herd. The milk fed to one group of calves was supplemented with an oregano essential oil-based feed additive at 10 milligrams per calf per day, included in both the morning and evening feeding (5 milligrams per 2.5 liters of milk twice daily). Calves were on this feeding regimen from 2 days old for 10 days, then calves resumed similar rations of milk and solid feed without any oregano oil.

Fecal samples were collected before and during feeding of the supplement, then every two weeks until weaning. The samples were analyzed for antibiotic-resistant E. coli, changes to the gut microbial profile, as well as cryptosporidium oocyst counts.

Calves fed the supplemented diet tended to have lower fecal E. coli levels, and they also shed cryptosporidium in significantly lower amounts.

With regard to antibiotic resistance, the resistance to amoxicillin, oxytetracycline, streptomycin or tylosin was similar between the two groups. However, there was also presence of E. coli resistant to cefquinome, a fourth-generation cephalosporin and one of the most critically important antibiotic treatments for infection control in humans. Calves fed the supplement had significantly lower levels of E. coli that were resistant to this antibiotic – about 70% less (41.2% down to 12.6%).

Improved the ‘good’ bacteria

As presented at the 2020 ADSA virtual meeting, following analysis of the gut microbiota, it was found that oregano essential oil-supplemented calves had higher levels of actinobacteria, which can be considered “good” bacteria and support good gut health. Alternatively, supplemented calves had lower levels of arthrobacter, which are generally aligned with adverse health events. These effects continued when testing concluded two weeks after supplementation ended.


In summary, supplementing calves with the oregano essential oil product reduced the presence of E. coli in the gut that were resistant to one of the most critically important antibiotics, while the presence of cryptosporidium was lower. At the same time, the levels of more beneficial bacteria were higher in supplemented calves.

It should be noted that while pasteurization does impact the levels of harmful bacteria in whole milk, it does not have a significant impact on antibiotic residues, which leads to searches for alternative methods, such as the use of nutritional supplements including oregano essential oil-based additives.

Beneficial bioactive compounds

Oregano essential oils contain bioactive compounds, and these beneficial compounds are generally higher and more diverse in natural oregano-based essential oils distilled from the whole plant. The active compounds work synergistically to offer well-documented antimicrobial benefits and have a complex mode of action which involves the breakdown of bacterial cell membranes.

In the study, calves were only supplemented for 10 days and at a higher dose (10 milligrams per calf per day versus a normal dose of 2 milligrams per calf per day). However, the benefits lasted with the calves through weaning. This suggests producers would be able to add the supplement to waste milk for a short period of time to gain longer-term benefits. There was no difference in intake at this higher level, and supplemented calves gained more weight in the first 10 days than calves that didn’t receive the oregano essential oil product.

Controlling antibiotic resistance takes a multifaceted approach that includes reducing antibiotic use on the farm. This takes input and advice from all stakeholders on the farm, including the veterinarian, nutritionist and other consultants who can help develop management protocols. This also includes engagement with critical staff to make sure protocols are followed to responsibly reduce antibiotic use.  end mark

PHOTO: Staff photo.

Mike Opperman is the owner of Black Dirt Communications.