SELECTIVE dry cow therapy is where only individual animals receive antibiotic dry cow therapy at the end of lactation and this selection is based on individual cow data.
It is intended to reduce antibiotic use and reduce the likelihood of antibiotic resistance. It is now being promoted by many of the UK milk buyers and forms part of the guidelines for Arla producers, where all farmers will have to take steps to move towards selective dry cow therapy.
Remember that dry cow therapy was introduced specifically to help eliminate subclinical infection at dry off. Over the years this was amended by adding in some Gram-negative cover to try to help prevent new infections occurring.
There can be no justification to administer dry cow antibiotic into a cow that is free of subclinical infection or that did not have a case of clinical mastitis in any quarter during lactation. If you look at milk records, you see that the proportion of cows with cell counts of over 200 is very small.
Trial work has shown that cows that are free from subclinical infection and are given antibiotic dry cow therapy in conjunction with a teat sealant will have a 12-fold increased risk of E. coli mastitis compared to a cow just treated with a teat sealant.
Selective dry cow therapy has been successfully used in many countries for many years. There is nothing to fear provided the correct guidelines are followed.
You need individual cell count data and accurate clinical mastitis records for decision-making on which cows should get antibiotics at dry off. Some herds don’t have individual cow cell count data but this should not be used as an excuse to continue with blanket dry cow therapy. Responsible use of antibiotics has to be based on sound science and not economics or the convenience of decision making.
Not every herd will be able to use selective dry cow therapy. Herds with high cell counts will still have to use blanket antibiotic dry cow therapy. These problem herds should be taking steps to reduce their cell counts, which offer more opportunities for vets. The median cell count of herds in the UK runs at below 180 at present, indicating the levels of subclinical mastitis are low.
Some herds will make their own guidelines, which can prove disastrous. Many years ago we had a client who decided to go down the selective dry cow therapy route without consulting us and his cell count increased from 150 to 350 over a period of 12 months.
He thought that a teat seal also contained antibiotics! It is very important that farmers work with their vets to ensure that sensible and sound decisions are made.
Some considerations to help decide if selective dry cow therapy is suitable at a herd level:
- Is the herd cell count under 200? If over 200, steps should be taken to reduce the herd cell count and blanket dry cow therapy used until this occurs.
- Do less than 25% of cows have cell counts over 200? If above 25% this suggests widespread infection and there is a greater risk of missing infected animals.
- Does the herd have a significant Staph. aureus problem? If so, use blanket dry cow therapy until this is resolved. It can be very difficult to identify all Staph. aureus cows.
- Is Strep. agalactiae present? If present, blanket dry cow therapy is recommended in the short term until levels have been significantly reduced.
- Are there low levels of Strep. uberis infection? If high, this would indicate that there will be many cows that have clinical and subclinical infections.
- Are individual cell count records available? If not, testing of individual animals should be started. This does not mean that they have to be tested monthly. Samples could be collected for the last three months before dry off.
- Are there accurate clinical mastitis records? There should be as it is a legal obligation. If not, the farmer should start to record all of these immediately.
Once you have established that the herd is suitable for selective dry cow therapy it is important to agree guidelines with your clients. This will be on a farm-by-farm basis using their history to make sound decisions.
There are a range of guidelines depending on which country or website you look at. In Ireland, the recommendation is to treat if any cell count was over 200 in the last three tests of lactation. In New Zealand, the recommendations for heifers are to have cell counts under 120 throughout lactation and under 150 for dairy cows.
All recommend that you use dry cow therapy in the quarter that had clinical mastitis. This is because cure rates for the Gram positive cases are low and it is important to clear up any residual infection.
You will always miss some cows with subclinical mastitis as any cell count test result is made up of milk from four quarters. A cow with a SCC of 150 might have individual quarter results of 30, 40, 50 and 600, where this high quarter has subclinical infection. However, this needs to be put into context, as the proportion of infected cows is relatively low. The risk decreases when the percentage of cows with cell counts over 200 is low.
A cow that does not receive antibiotics at dry off should be given an internal teat sealant to minimise any risk of mastitis in the following lactation. In fact, every cow that is dried off will benefit from internal teat sealants. These reduce the levels of clinical mastitis in the next lactation by between 25 and 30% and offer an excellent return on investment where the farmer clearly sees the benefits.
All of the above shows that there is significant opportunity for vets to work with their dairy clients and guide them through the selective dry cow therapy maze. This is important from the outset but also on a continuing basis to ensure that correct decisions are being followed and that there are no adverse effects on mastitis.
It is down to the profession to be proactive in this approach to selective dry cow therapy.
- The next Mastitis Control and Quality Milk Production Seminar run by Peter Edmondson and Roger Blowey will be held from 8th to 10th November. See www.sheptonvet.com for more details.
