DRY COW THERAPY (DCT) AND RESIDUES
Dry off

Dairy company records indicate that this is the worst time for expensive (high level) inhibitory substance (IS) grades. This is mainly due to DCT treated cows being accidentally milked.

Fonterra has recommended a number of steps to reduce the chances of your farm grading for inhibitory substances at dry off.

Always follow the advice given by your veterinarian, and the label instructions of the DCT. Following the steps of the Guide To A Great Dry Off will help ensure that no problems occur.

Ensure that all farm staff know how DCT treated cows are identified, and what to do if a DCT treated cow is found in the herd. If contamination is ever suspected, contact the dairy company and have the suspect milk tested prior to the next collection.

Start of supply

Some inhibitory substance grades that occur at the start of the season have been attributed to the presence of DCT residues. Remember that DCT has a pre and post-calving milk withholding period.

The pre-calving withholding period is written on the label of the DCT (this varies between 28-56 days).

The post-calving withholding period is a compulsory eight milkings. Both these periods must be followed to reduce the chance1 of inhibitory substance grading.

Investigations into early season grades show that the risk may be increased if:

  1. Cows are treated whilst producing low volumes (Fonterra19 suggest, volumes less than 5L at dry off are associated with an increased risk of a residue violation)
  2. Dry quarters are treated at dry off
  3. More than one treatment is given at dry off
  4. Cows are treated with DCT during the dry period
  5. Very low volumes are supplied at first collection
  6. Individual cows are producing lower than expected volumes of milk (e.g. with metabolic disease or cows that have slipped)
  7. A number of cows have calved inside the minimum treatment to calving interval (especially if the rest of the cows are close to the minimum interval).
If the herd falls into any of the risk categories listed above, it is recommended that milk be tested prior to the first collection.

To supply the highest quality milk, the first milking into the vat must be agitated. Depending on the vat size, as much as 400L of milk may be required to achieve full agitation. Fonterra recommends suppliers aim to supply at least 1,000L at the first collection of the season.

Supplying this volume will significantly reduce the chance of grading for bacteria, Somatic Cell Count (SCC) and added water. It will also reduce the chance of grading due to the presence of DCT residues.

If a farmer ever receives an IS grade, they should contact their veterinarian, who will be able to help their avoid a reoccurrence.

1
Malcolm D (2006). The cost of mastitis study. Proceedings of the SAMM Milk Quality Conference.
19
Fonterra Farmlink Magazine (2007).