Changes in tetracycline for digital dermatitis
Several changes in the way dairy farms can use antibiotics came into effect January 1st, 2017. At this point, most people are aware of the Veterinary Feed Directive (VFD) and the effect it has on some of the practices we used in raising replacement heifers. The same legislation that brought in the VFD also changed access to certain over-the-counter (OTC) drugs. One of the drugs affected by this change were the tetracyclines that hoof trimmers commonly used to treat digital dermatitis (hairy heel warts). On top of this, it is expected that at some point in 2017, the National Conference on Interstate Milk Shipments (NCIMS) is going to start a pilot tetracycline testing program. This pilot program will test 1/15 of all grade A raw milk for tetracycline residues on a quarterly basis.
What does this all mean for your farm? Primarily you will notice that your hoof trimmer will no longer be able to show up on your farm with tetracycline powder that they purchased themselves and farms will have to supply it. Unfortunately, there are no antibiotics with a licensed label claim for the treatment of digital dermatitis. This means that the use of tetracycline to treat these cows is considered extra-label drug use.
For farms to be able to continue to use tetracycline powder, the farm will need to get their veterinarian to write a prescription. To write a prescription, your veterinarian will require the farm to have a veterinary client patient relationship (VCPR). The VCPR means that:
- The veterinarian is familiar with the client (farm owner)
- The veterinarian is familiar with the herd being treated
- The client must agree that the people who use antibiotics on their farm (including hoof trimmers) follow the veterinarian’s specific directions.
A prescription needs to include:
- A dose
- An application method
- Appropriate milk and slaughter withdrawals information
To ensure your farm continues to use antibiotics responsibly and is not affected by the change in both access to tetracycline powder and the pilot testing program, it is important that your veterinarian and hoof trimmer communicate and develop a treatment protocol that they are both comfortable with. Your veterinarian will want to be certain that the specific instructions they provide on their prescriptions are followed to ensure the milk withdrawal period is appropriate.
Research conducted at the University of Minnesota has shown that treatment with tetracycline powder does create residues in the milk and teats do become contaminated with the treatment. This raises some questions for veterinarians writing prescriptions and they will want to ensure a system exists to ensure proper dosages are used to prevent violative residues.
Figure 1. Example of three different tetracycline dosages. 25g, 5g, and 2g (from left to right).
A violative residue is a residue that is above the maximum residue limit (MRL) of 300 ppb for tetracycline. From this University of Minnesota research, we know that applying 2 grams or less of tetracycline powder per lesion for a maximum of two lesions per cow will not cause violative residues in individual cows and is enough to successfully treat the lesion (Figure 1). A complicating factor is that although the MRL is 300 ppb, some of the tests used to screen milk can detect tetracycline residues at a much lower level. What you and your veterinarian will need to consider is how your milk processor is going to implement the NICMS pilot program and how they will use the results of tests that find tetracycline residues below the MRL. In most cases, if an appropriate dose of tetracycline is used on individual animals, the risk of contaminating the food supply with violative residues is minimal. However, in some cases, your veterinarian might be uncomfortable with the risk of potentially contaminating the milk supply and include a milk withdrawal period.
The bottom line in all of this is for you to be sure your hoof trimmer and veterinarian have developed a protocol that ensures cows with digital dermatitis receive appropriate treatment and also address the new rules around the use of and testing for tetracycline.