10 Common Reasons Antibiotic Contamination
Occurs in Bulk Tank Milk
1. Milk from a treated cow was accidentally routed into the pipeline.
Err on the side of safety! Accidents and human error are unfortunate
events but the end results (milk residues) are still violations. Treated cow
identification protocols need to be farm-specific and standardized so all farm
personnel can readily distinguish a medicated cow. When a cow needs medication,
the first treatment step (before any medications are administered) should be
the application of some form of semi-permanent identification. At least two
different identification methods should be employed. These may include leg
bands, chalk marks, tail tape, neck chains, or some other form of secure
identification that can be easily removed when the withholding time has
2. Antibiotic residues remained in the milk of a recently fresh cow (that
had previously received dry cow therapy) or a treated cow longer than the
presumed withholding time.
When drugs approved by the federal Food and Drug Administration (FDA) (for
dry and lactating cows) are used according to the label directions, producers
should follow the recommended withholding times. Extensive product evaluations
by drug manufacturers have built safety factors (required by the FDA) into the
established withholding times. These safety factors are 100 to 1,000 times
lower than the lowest dose expected to cause a violative residue in milk.
Drugs used in an extra-label manner MUST be used within the context of a
valid veterinarian-client-patient relationship. Extra-label treatments
DO NOT have established withdrawal times; therefore, the prescribing
veterinarian must supply a withdrawal time for meat and milk sufficient to
assure food safety. Administering two or more FDA-approved drugs into one cow
simultaneously is considered extra-label use and may result in violative
residues. Even though FDA-approved medications are used according to label
directions, extended withholding times may be needed for cows that calve
earlier than expected, cows that are severely ill or cows that do not respond
to label treatments.
3. Equipment used to milk treated cows was handled carelessly; for
example, vacuum from the milk pipeline was used operate dump-milk buckets.
Milking all treated cows AFTER untreated herdmates is an important
preventive measure and strongly advised. Dump-milk buckets connected to
pipeline vacuum can overflow or be tipped, allowing contaminated milk to enter
the system. Frequent disposal of contaminated milk from dump-buckets may reduce
the potential of overflow into the pipeline.
4. Lactating cows were purchased and the new owner was unaware of recent
antibiotic treatments prior to sale.
Although milk residue tests are not designed or approved for individual cow
testing, milk from all purchased cows should be evaluated for residues by a
test kit that detects the same drugs as the farm's milk processor. This should
occur before commingling purchased-cow milk in the bulk tank. Milk should from
all cows testing positive should be discarded. It may be prudent to discard
milk from purchased cows for at least eight milkings regardless of milk residue
5. The same milking unit was used to milk an antibiotic-treated cow
before milking untreated cows. The milking unit was not cleaned and sanitized
When in doubt, dump it out! Using the same milking unit on treated
and untreated cows without thoroughly cleaning and sanitizing between cows is a
violation of the pasteurized milk ordinance (77 ILL. ADM. CODE 775). Extremely
small quantities of contaminated milk can result in bulk tank residues. Milking
treated cows last is a wise practice. If facilities do not allow isolation of
treated cows, a separate, labeled hospital-unit connected to a dump-bucket can
6. An antibiotic-treated dry cow was unintentionally milked.
Segregate treated dry cows from lactating cows, preferably in a separate
facility. Physical isolation will reduce the potential for unintentional
commingling of treated dry cows with the lactating herd. The farm-specific,
two-way identification system mentioned previously should make it simple for
milking personnel to easily recognize antibiotic-treated dry cows.
7. All antibiotic-treated cows were milked last, but the milk line was
not diverted from the bulk tank.
Prior to milking, a treated-cow list could be hung from the bulk tank swing
line. Temporary parlor (milking) down-time should occur between milking
untreated herdmates and treated cows. Even if untreated cows remain in the
parlor as "place-holders," all milking units should be removed and
readied for the medicated milking string. To retrieve the treated-cow list from
the swing line, one must enter the milk house. Before removing the treated-cow
list, pull the swing line out of the bulk tank. Use the treated-cow list to
cross check the remaining cows to ensure that all treated animals have been
8. Cows drank from a medicated footbath.
The practice of using medicated foot baths to control hoof diseases has
little scientific basis. Once manure accumulates in the foot bath solution, the
efficacy of the medication may dramatically be reduced. Treating individual
lame cows with sprays and/or corrective hoof trims may offer better results and
reduce the potential for residues.
9. Medicated feed was accidentally mixed into the lactating-cow feed.
Medicated feeds should not be used to control diseases in lactating dairy
cows. The diseases for which medicated feeds were developed can be
controlled through improved environmental and nutritional management. If
medicated feeds are used on the farm for non-lactating animals, store them in a
separate facility from lactating-cow feed ingredients.
10. One quarter of a cow was treated for mastitis and withheld from the
bulk tank. However, milk from the other three quarters was NOT withheld and was
permitted to enter the pipeline.
All FDA-approved drugs designed for intramammary use will be absorbed into a
cow's bloodstream after infusion into a quarter. The bloodstream carries the
nutrients used to produce milk within the udder. Antibiotics absorbed into the
bloodstream can also be transferred (along with nutrients) to all functional
quarters. Discard milk from all four quarters, regardless of which quarter
Supported by Illinois Department of Public Health, Drug Residue Penalty Fund
Sponsored by the Illinois Dairy Field Representative and Sanitarian Association
and the University of Illinois Extension at Urbana-Champaign