Antibiotic DCT is used to cure existing bacterial infections. Cows with ICSCC>150,000 and heifers with ICSCC>120,000 at any herd test during the season are deemed to be at risk of harbouring a significant bacterial infection. (These figures were derived from NZ studies completed by R Holdaway in the late 80's and early 90's).
Antibiotic DCT also prevents new udder infections over the dry period by the physical presence of antibiotic in the udder; and also by increasing the rate of keratin test plug formation sealing the dry quarter against outside contamination.
The keratin plug is very important in preventing new infection in dry cows. However, as calving approaches, teats start to lose their keratin plugs in preparation for milk flow, even in cows treated with antibiotic DCT. The advent of teat sealants provides a very useful tool in the prevention of new infections over the whole dry period.
All well manufactured DCT products effectively clear the majority of infections in the typical NZ herd at the end of the season. Even the shortest short-acting products are active in the udder in excess of 21 days, enough time to drive cure rates above 80% for most bacteria. However short-acting product activity drops off relatively quickly so that after five or six weeks prevention of infection in the udder relies more on keratin plug integrity than the presence or absence of antibiotic. In a cow with an 8-10 week dry period this decrease in activity usually coincides with the increased infection risk as teats start to open in preparation for the new lactation and with time spent on feed pads or stand-off areas where contamination is an issue. This is where long-acting therapy or combination therapy with a teat-sealant comes into its own.
Long-acting therapy or combination therapy provides a good "kill" at the end of the season and also good prevention out to ten weeks. Where the dry period is going to be substantially longer than ten weeks, combination therapy with a teat-sealant will provide protection for the duration of the whole period.
The key information to enable your vet to correctly prescribe DCT for your farm includes:
- the number of cases of mastitis in the first week following calving;
- herd test cell count information;
- bacterial culture results (make sure your bugs are susceptible to the drugs);
- length of dry period; with-holding periods;
- the approach of staff inserting DCT to hygiene and detail.
Did you know that your approach to drying off cows has a major impact on the amount of mastitis you will get at calving?
Up to 30% of mastitis cases around calving are due to bacteria that infected the udder at dry-off. The bacteria can sit happily in the udder, not causing visible signs, until the cow’s immune system is stressed and a large source of food is available (i.e. milk!), both of which occur at calving. Suddenly the bacteria have the ideal environment to multiply to a level that result in clinical mastitis.
All DCT products should be administered according to strict hygiene protocols set out in the packaging as the consequences of taking short cuts can be more severe for some products than others.
Here are some tips:
- Use dry-cow therapy (DCT) and/or Teatseal™ to protect the quarter until the keratin plug forms
- Ensure you are scrupulously clean when inserting DCT or Teatseal™ into quarters. The bottom 2cm of the teat should be so clean that you would be happy to drink from it! Any dirt left at the teat-end can result in nasty bacteria infecting the gland. Many of these bacteria are not sensitive to dry-cow antibiotics and can cause severe illness and death
- Be as gentle as possible and introduce only 3mm or less of the tube nozzle into the teat when using intra-mammary tubes. This will minimise damage to the teat sphincter; the tissue that produces the keratin plug
- Keep DCT syringes dry when drying-off. If you need to warm syringes to facilitate insertion of the DCT, do so by placing hot water bottles in the bucket of syringes
- Ensure cows are dried off onto clean pasture – keep them away from effluent-sprayed and wet paddocks. Try to minimise break-feeding in the first week as this tends to result in high faecal contamination of udder and teats
- Keep cows away from the shed for at least a week. This is to prevent involuntary milk let-down that could potentially upset the formation of the keratin plug. Dripping milk also acts as a great wick for bacteria to enter the gland
- Don’t bring cows onto a feed pad for at least 10 days and ideally longer, as faecal contamination make pads great breeding grounds for the bacteria that cause mastitis
- Do not use skip-a-day milking before drying off, as studies show this increases mastitis
- Do not restrict access to water to reduce milk production – water must be freely available at all times
- If cows are doing over 12 litres at dry-off, a change of feed should be included in you dry-off plan to reduce the level of milk production by the gland. Talk to one of our vets to discuss the most appropriate plan for you.