Use of residue containing raw milk as feed

Every year, Finnish dairies reject about half a million litres of raw milk due to suspected
antimicrobial drug residues discovered in their own checks. This milk cannot
be used for human consumption, but is normally used as animal feed. Safety of this raw milk used as feed for pigs and calves was estimated in the risk assessment.

Conclusions

1. Antimicrobial drug residues in test-positive raw milk rejected at the dairy and feed
made from this milk do not pose a toxicological health risks to pigs and calves in
the current situation.
2. When raw milk from a transportation truck is tested at the dairy, possible drug residue
concentrations have been diluted to the extent that in practice residue test
can only detect ampicillin, benzylpenicillin, cephalexin, and cloxacillin. Aminoglycosides
and novobiocin are used in cattle only in combination with benzylpenicillin
and cephalexin, so even though residue test at dairies cannot detect aminoglycosides
and novobiocin, they might end up in feed via raw milk testing positive for
benzylpenicillin or cloxacillin residues.
3. Since the antimicrobials mentioned in point 2 constitute the majority of antimicrobials
used on cattle, with the help of the dairy test it is possible to prevent a
significant portion of raw milk containing antimicrobial drug residues from going
via prepared food stuffs to the consumer.
4. According to the assessment, concentrations of antimicrobial drug residues other
than those mentioned in point 2 have, by the time they arrive at the dairy, been
diluted to the point where they are under the maximum residue limits (MRL) set
by the EU.
5. The heat-treatment of raw milk or the acidification of feed do not significantly
decrease the concentrations of antimicrobial drug residues. On the other hand,
treating raw milk with ß-lactamase enzymes effectively lowers the concentrations
of benzylpenicillin and aminopenicillins, but it has no effect on other antimicrobial
drug residues.
6. The risks to consumers from the use of raw milk containing antimicrobial drug
residues as animal feed is not considered in this report. However, based on the
very low exposures of animals to these residues we can conclude that the risks
of human exposure to antimicrobial residues via pork or beef meat are very
small in the current situation.
7. When using raw milk rejected due to a positive test for antimicrobial drug residues
as feed, Intestinally-carried campylobacter, enterohemorrhagic E. coli
(EHEC) and Listeria monocytogenes are possible hazards, which may warrant
a further risk assessment.

Research group

Ulla Karlström (EELA/Evira)
Lasse Nuotio (EELA/Evira)
Laura London (EELA/Evira)
Riitta Maijala (EELA/Evira)

Publications

U. Karlström, L. Nuotio, E. Lindfors, R. Maijala (2007). Simulation of human exposure to benzylpenicillin residues via pork originating from pigs fed with a dairy by-product. Food Additives and Contaminants 24(3): 266-273.