Will Heat Treating Decrease Viability of Antibotics
in Waste Milk? Don't Depend on It!
In a recent issue of a popular dairy magazine I read this paragraph:
"Veterinary researcher Richard Van Vleck, a member of the Cornell research team [reference is to team headed by Warnick doing research on antimicrobial resistance] suggested pasteurization is a viable means of degrading antibiotic residues to considerably lower levels, which could significantly reduce the influence of antibiotic presence in calves' gut flora."
Since I was unaware of this work I dug it up (Plos One DOI:10.137/journal.pone.0115223 December 15, 2014 "In Vivo Selection of Resistant E. coli after Ingestion of Milk with Added Drug Residues) by Richard Van Vleck Periera and Others. They were looking for changes in E. coli resistance to drugs when calves were exposed to 4 different levels of 4 selected antibiotics. They found that at all levels of exposure to drugs the E. coli in the gut were more resistant to 5 selected antibiotics than in calves with no drug exposure. All calves were fed raw milk.
I did not find any data in the article support the reported connection between pasteurization and the influence of antibiotic exposure in developing drug-resistant E. coli. But, this got me interested in the extent to which heat treating waste milk is related to decreasing the effectiveness of antibiotics in waste milk fed to calves.
I dug some more and found this article;
M. Roca and Others, "Effect of heat treatments on stability of beta-lactams in milk," Journal of Dairy Science 94:1155-1164. (2011)
Two of their findings:
1. "Heat treatments at high temperatures and long times (e.g, 120C for 20 minutes) led to a further degredation of beta-lactam antibiotics with percentages close to 100 percent for cefoperazone and cefuroxime."
If you are not familiar with 120C that's about 248F.
2. "When milk was subjected to heat treatments at lower temperatures (e.g., 72C for 15 seconds), the degradaton of beta lactams in milk did not exceed 1% for the 10 antibiotics tested." (emphasis added)
If you are not familiar with high-temperature, short-time pasteurization on-farm pasteurizers, 72C for 15 seconds are the "normal" temperatures and times used to process waste milk for feeding calves. Batch pasteurizing waste milk is usually done at a lower temperature for longer period of time, 145F for 30 minutes.
What do I conclude based on their findings? Given normal on-farm processing of waste milk containing antibiotic residues there is virtually no effect of the pasteurization process on the antibiotics in this milk. That is, after pasteurization these antibiotics remained effective in suppressing the growth of certain sensitive species of bacteria.
From a management point of view, therefore, I am inclined to recommend that sources of waste milk with high concentrations of antibiotics be diverted from the "calf milk" supply. The single most obvious source is the first milking after cows have been treated with an intra-mammary infusion of mastitis drugs - milk it out down the drain.
Just more food for thought for calf managers.