Avoiding inhibitory substance grades Part 1

Part one - Around drying off

The majority of inhibitory substance (IS) grades are attributable to risky on-farm management practices particularly relating to the periods of time around drying off and/or calving. This is when most antibiotic grades occur and are most frequently as a result of cows recently treated with dry cow therapy (DCT).

There are a number of steps that can be taken to minimise the risk of grading particularly around drying off.  These include:

  • Allow time, have adequate numbers of capable staff on-hand, ensure that cows are clearly identifiable and their numbers are recorded adequately.
  • Only infuse DCT once all cows have been milked. Bring cows back in immediately after milking, once all cups are off.
  • If cows are dried off in batches, make sure treated cows are kept separately and are well away from the milking herd.
  • Make sure everyone knows how treated cows are marked and what to do should any treated cows re-enter the herd.
  • Any suspicion that contamination of the vat has occurred - contact the dairy company. This may save getting a grade or lessen the penalty imposed.

Every DCT season we invariably have a number of calls asking what to do if a cow has inadvertently  received double treatment. To decrease this risk mark treated cows clearly and have a pre-determined order of administration of DCT (eg. BL-BR -FR-FL). Administering two tubes of DCT to a quarter alters the antibiotic residue profile and increases the risk of an IS grade at the start of the season.

The volume of milk a cow produces toward drying off affects how antibiotic behaves in the udder. DCT applied to cows once dry will produce extended periods of antibiotic residue in milk post-calving. Individuals that are producing less than five litres per day (or <0.4kgMS/cow/day) are getting close to drying themselves off and are likely to have prolonged residue profiles.

Provided with-holding periods are complied with and stock are well managed IS grades are avoidable and penalties are rare. To complete the picture, check out Part two - Around calving.