Watch Your Withdrawal Periods
Michael Fisher, Area Extension Agent (Livestock), Colorado State University Extension
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Do you know what the withdrawal period is for the various animal health products that you administer to your livestock? For that matter, do you know what a withdrawal period is established for?
As livestock producers, we are the first line of defense in ensuring that the American meat supply is a quality, wholesome, and safe product. To help meet that goal, withdrawal periods have been established for many of the animal health products that are used in livestock production. This is a period of time beginning with the administration of a pharmaceutical product and lasting a set length that has been pre-determined by the Food and Drug Administration (FDA). The idea is that any pharmaceutical compound has a maximum allowable amount of residue that can be in the meat product or milk. The withdrawal period allows a period of time for the compound to be broken down within the animal following its administration. Neither meat tissue nor milk can be used from an animal that has a drug residue which exceeds the maximum residue limit (MRL) that has been set for that given compound. In other words, the withdrawal period is an opportunity for a treated animal to be in compliance with the MRL at the time of harvest or milking.
The FDA has established the MRL for the various medications based on several different locations within the animal. The residue source that is examined is dependent upon what medication is being monitored. As an example of the differences, Pfizer’s Draxxin (active ingredient: tualthromycin -18 day withdrawal) has a MRL of 5.5 parts per million (PPM) in the liver; while Elanco’s Tylan injection (active ingredient: tylosin – 21 day withdrawal) has a MRL of 0.2 ppm in fat, muscle, liver, and kidney. Pharmaceutical companies, under the FDA’s guidance, have to conduct trials to determine how much time it takes for a given compound’s residue to be at or below the assigned MRL following treatment of the animal. If the time needed ends in a fraction of a day, the withdrawal period is expanded to complete that day.
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