Recently, the FDA sent ripples through the dairy industry by proposing to begin surveillance of bulk milk for residues for 26 pharmaceuticals. The number of farms and target population for samples was based on farms that have had a past history of residues in meat. While many affiliated with the dairy understand the reason that FDA might want to check for a broader category of residues in milk, there is concern that very sensitive tests might find extraordinary low residues. Some compounds are used in Europe and withdrawal times can be estimated from that data. These estimates might be safe and appropriate based on solid scientific data from Europe. However, in some cases the levels may not match the proposed levels suggested for testing by the FDA. Holding milk for extended periods while the tests are conducted or perhaps finding these low levels could cause considerable challenges for the industry. 

The amount and length of time residues can be found in meat or milk varies for a large number of reasons. First, time for withdrawal or withholding is based on data obtained on healthy animals.  Nearly all pharmaceuticals are eliminated by the liver or the kidneys. If these organs are damaged, if the animal is severely dehydrated, or even if the animals is off feed for a period of time, any of these factors  can significantly extend the time it takes for the animal’s body to excrete a compound.  Second, dosages at levels (mg/lb or mg/kg) higher than listed on the label will create prolonged residues. Thirdly, some products have specific residue data established for certain species, and this cannot be translated exactly one for one between species (dairy cattle and dairy goats). Finally, giving the product in tissue as listed on the label vs. a different route. This creates a different dynamic in the animal and changes withdrawal and withholding times.

A common issue in the residue controversy right now is the use of flunixin megulmine (Banamine ®, Schering Plough) either IM or SQ vs. the label directions for IV use. As described above the use of any pharmaceutical differently than described on the label or in a food animal species not on the label is considered an extra label use drug (ELUD). Such use can only proceed under the written or oral instructions of licensed veterinarian in a valid client patient relationship (VCPR). This use is permitted only under the regulations established by the Secretary of Health (Section 340).  A key feature in the rule making is that ELUD cannot increase risk to public health.  Economics and convenience are not considered as key features that should alter the risk to the public even if only slightly.

The privileges and responsibility for the use of pharmaceuticals was outlined in the Animal Drug Use Clarification Act (AMDUCA) 1994. Public health and consumer confidence were important considerations in the passage of this bill. Clearly the veterinary practitioner and the producer must work more closely together to ensure that the letter and the spirit of the AMDUCA legislation are upheld. Over the past few years an increasingly large array of products have become available to the dairy producer with minimal oversight and /or the development of treatment protocols by the private veterinary practitioner. Some products are not detected by on farm screening kits or they may be detected at levels different than more sensitive or specific testing strategies employed by regulatory agencies.

It is extremely important for the dairy industry to maintain consumer confidence that every effort be made to ensure that residues in milk are avoided. In nearly all cases where residues have been found in the meat of market dairy cattle or bob veal calves, trace backs reveal some deviation from normal in therapeutic strategy or lack of extended withdrawal times. Increased efforts to ensure treatment protocols are followed which conform to ELUD and AMDUCA and guidelines should be promoted and adhered to by all members of the dairy industry. As necessary it is very important that extended withholding times are used whenever therapeutics are used at levels or in methods that would constitute ELUD. Extremely sensitive tests are available and can detect residues that might have been overlooked in the past. 


  • FDA and the Veterinarian, US Dept. of Health and Human Services, CVM, Feb. 2000
  • McKean, JD, Revisiting AMDUCA, Swine Practitioner, Jan. 2006, pp. 2-5
  • Reig, M and F. Toldra, Veterinary drug residues in meat: Concerns and rapid methods for detection, Meat Sci., No. 78, July 2007, pp 60-67
  • Smith, G.W., et al., Extra label use of nonsteriodal anti-inflammatory drugs in cattle, JAVMA, Vol. 232, No. 5, March 2008, pp. 697-701

Dr. David Wolfgang, Extension Veterinarian, Penn State Department of Veterinary and Biomedical Sciences