Extra Label Drug Use & Antibiotic Residues
In The Milk? Caution!

You’ve tested the milk from a cow you’ve treated with antibiotics. The test proves negative. So it is safe to ship her milk, right? Maybe not. If her treatment was extra-label drug use, there is still a risk of residue showing up in your bulk tank.

Should a test prove positive for antibiotics, it could take a huge bite from your bottom line. The present penalty system calls for a $6, $9,or $12/hectoliter fine for 1 months’ shipments plus the cost of the tanker load if it also tests positive. Needless to say this can run into thousands of dollars.

Residues not only present a problem to the producer but also to the processor if the residues inhibit the fermentation process necessary for the manufacture of some dairy products. Because of the concern over the potential impact of residues in milk, manufacturers of antibiotics are required to provide guidelines for withholding milk from treated cows.

In Ontario the incidence of positive inhibitors is very low at approximately 0.12% of producers samples (1998 monthly average) but when a positive inhibitor happens it feels like a 100% to that producer.

Producers react in one of two ways when notified of inhibitors in their milk. One way is acceptance because they know exactly what happened to have caused the positive test. The second reaction is disbelief, anger and confusion. Often this is as the result of not immediately knowing what caused the positive antibiotic test.

A survey reported in J.Dairy Sci.70:2176-2180 and 1995 International Dairy Federation pp.28-31 identified some of the factors that contributed to residues in milk including:

• Lack of communication among staff or family members
• Inadequate records
• Accidental feeding of medicated feed
• Extra label drug use

The last point is of particular interest as there is often misunderstandings of what is considered "extra label" drug use and these misunderstandings can lead to antibiotics being found in the bulk tank. Dr. Rob Tremblay of Boehringer-Ingelheim states that extra label drug use is use of a product in any manner that’s different from the instructions on the label or package insert. Withdrawals times stated only apply when the product is used exactly as the label indicates.

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Dr. Tremblay points out the following are all considered extra label drug use:

• Using a dose different from the dose on the label such as giving 3 ml/kg if the label states 1 ml/kg
• Giving at a different frequency, e.g. twice per day; if once daily is recommended on the label
• Treating for a longer or shorter time than recommended
• Using a different route of administration, e.g. giving a product under the skin when it’s intended to be administered in the muscle
• Giving to a different species or class of livestock, e.g. Using products intended for swine to treat cattle or using products intended for feedlot cattle to treat lactating dairy cows
• Using the product to treat a disease not listed on the label

It is important to remember that the use of drugs by producers in an extra label manner can only be under the direct supervision of a veterinarian. In many provinces the veterinarian is required to provide written instructions on any extra label use of the livestock medicine-including an appropriate withdrawal time.

Information from a research paper by L.J. Fisher, M. Wetstein, J.A. Shelford & D.L. Dyble published in the proceedings of the 1998 Pacific Northwest Animal Nutrition Conference shows the link between extra label drug use and positive inhibitor tests. In one research trial, two groups of four lactating cows were injected with either 1.1 or 3.75 ml of Ethacillin (one of several injectable preparations of procaine penicillin available to dairy producers in Canada) per 45 kg of body weight ( 1.1ml/45 kg is the label rate which translated into 15-16ml/cow). Each group of cows was given their treatments over four days with the injection site changed each day. For the cows getting the extra label dose (approximately 60 ml) the penicillin was given as four injections within each site to minimize the chance of excessive tissue damage.

The researchers found that at the recommended dosage all four cows were clear of residues within 48 hours of the last treatment. For those given the extra label rate, one cow was clear at 48 hours, one cleared at 72 hours but than had a positive milk sample at 96 hours while the other two cows remained positive at 120 hours after the last treatment.

The researchers than repeated the trial with five cows given the higher dose of Ethacillin. Two cows were clear within 48 hours while one was clear after 72 hours of the last injection. Milk from the other two cows was negative for 3 and 5 milkings respectively but than became positive again. These results they point out, provide further evidence that extra label drug usage of an antibiotic may result in longer and UNPREDICTABLE secretion times.

The fact that three out of four cows had a one or more negative tests followed by a positive test indicate that clearance of penicillin used extra label may not follow a predicted pattern. The researchers further point out that in another study by R.J. Krainock (J.Am. Vet.Med. Assoc. 198:862-863) where 35 ml of Ethacillin was given at one injection site, it resulted in the formation of an abscess and the occurrence of inhibitors in the milk for up to 20 days post injection.

The researchers conclude that whenever drugs are used in an extra label fashion, the milker should be informed and milk not be allowed back in the tank until it has been shown to test negative for four consecutive milkings.

Antibiotics can be a valuable management tool but precautions must be taken to ensure that unacceptable levels of residues do not appear in the milk supply for the consumers, processors and the producers sake.

Related Links

• Troubleshooting Antibiotic Residues in Milk and Dairy Beef

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