Feeding waste milk to calves and impact on the development of antibiotic resistance – Defra research

25 Aug 2017

In recent years bacteria, particularly E. coli, have emerged with resistance to 3rd and 4th generation cephalosporin antibiotics. These antibiotics are widely used as front line treatments in human medicine and the development and dissemination of bacteria resistant to these medicines is a serious medical problem. This resistance is mainly conferred by the production of enzymes and there are large numbers of different enzymes which may be involved, but one large group of important enzymes comprises the Extended Spectrum Beta Lactamases (ESBLs).

Ongoing surveillance studies at the Veterinary Laboratories Agency have revealed a number of farms where ESBL E. coli are present and on those farms, resistance is particularly common in young calves. However, cephalosporin antibiotics are often less commonly used to treat calves (although related aminopenicillins may be used) and this has led to the suggestion that exposure to these medicines may occur through indirect routes. Calves are often fed waste milk which may contain antibiotic residues. Waste milk is unfit for human consumption and is discarded at milking; waste milk may contain colostrum, milk from animals with mastitis or milk containing antibiotic residues. Cattle may be treated with antibiotics for a wide range of infections but mastitis is a very common problem in the dairy industry.

The following deliverables were identified for this study :-
1. Current farming practices relating to the use of antimicrobials in dairy cattle and feeding of waste milk.
2. Assessment of the risk of antibiotic residues in waste milk promoting ESBL selection.
3. Concentrations of antibiotics likely to be found in waste milk.
4. Practical and economic recommendations for farmers to substantially reduce the risk of development of
ESBL resistance arising from the feeding of waste milk to calves.

The conclusion of the study was that completely stopping the feeding of waste milk was considered the most effective method in a number of scenarios. Most farmers who do not feed waste milk feed milk replacer as an alternative, which would be an additional cost. However, although the calves fed waste milk in this study showed less disease, feeding milk replacer is likely to have health benefits, particularly in preventing Johne’s disease but also in the control of other important diseases such as Mycoplasma bovis infection and salmonellosis. Other alternatives were also considered which would result in the elimination or reduction of cephalosporins in waste milk fed to calves. These could involve not using cephalosporins in the herd or managing waste milk so that milk containing cephalosporins or milk containing higher concentrations of cephalosporins is not fed to calves.

A range of treatments of waste milk to reduce the concentration of cephalosporin were also reviewed and it was considered that a treatment that eliminated cephalosporin residues and ESBL E. coli would, if developed produce similar results to not feeding waste milk. These treatments of waste milk all require further work to establish if they would be practical solutions on farm. The possible environmental effects of disposing of unused waste milk containing antibiotics in slurry or wastewater require further investigation.

Keywords: dairy, antibiotic, waste milk, feeding, calf, calves, milk replacer, antibiotic, resistance, critically important antibiotic, cephalosporin.


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