First find out whats wrong
Keen to reduce the cell
count of your cows milk to
maximise milk payments,
but struggling to get there?
Sue Rider asks a top
mastitis vet how to
win the battle
KNOW whats causing a high somatic cell count in milk before attempting to deal with the problem.
This is the first step towards reducing cell counts and its an essential one, according to vet Peter Edmondson who runs a mastitis and milk quality consultancy service in the UK.
"A mechanic doesnt automatically change the exhaust when the tractor is smoky – he first finds out whats wrong and then fixes it." The same should be true when tackling high cell counts in milk.
Individual cow cell counts will help pinpoint the culprits. Mr Edmondson advises collecting milk samples from six to 10 high cell count cows and taking a sample from the bulk tank.
Bacteriology tests on these samples will then identify the main mastitis bacteria present in the udder (see box overleaf).
Once the main type of bacteria has been identified, you can plan how to deal with infected cows, and how to protect the rest of the herd.
Culling would eliminate problem cows immediately. But the difference between cull and replacement value makes it a costly strategy and one that should never be based on cell count alone.
Sometimes sub-clinical mastitis can be tackled by treatment, but this depends on the type of bacteria causing the high count. The main culprits are the bacteria Staph aureus (S aureus), Strep agalactiae (Strep ag) and Step dysgalactiae.
Strep ag is the easiest of the three to tackle, admits Mr Edmondson. Treatment will be successful in reducing the count so culling would be very expensive in this instance.
"The good news is that Strep ags very sensitive to penicillin; blitz therapy can be used to eliminate the bug from milking herd."
When using blitz therapy intramammary antibiotics are infused into all four quarters of the udder – either of the entire milking herd or into a group of selected animals (see case study 1). All cows must receive dry cow therapy.
To be successful, Strep ag must be the culprit, and steps must also be taken to reduce spread of infection throughout the herd.
"Strep ag is highly contagious, so the rest of the herd must be protected from infection before individual treatment begins."
This requires good hygiene practices in the milking parlour – fresh paper towels for each cow instead of udder cloths, careful teat dipping after milking, and changing liners at least every six months.
Hands are a common source of mastitis infection, particularly when the skins cracked. Mr Edmondson suggests wearing disposable gloves – and rinsing gloved hands in disinfectant during milking to avoid cross contamination.
To ensure infection that may have been transmitted onto the teat during milking doesnt infect the udder, post-milking dipping or spraying is vital – and the sooner after taking off the cluster the better. "Whichever method is used, ensure the entire surface of the teat is covered – use of an iodine solution will help in this respect," advises Mr Edmondson.
An effective milking routine is also required to control the other main mastitis bug – S aureus – responsible for high cell counts. Like Strep ag it is highly contagious.
"S aureus infection can spread to the next six to eight cows from the liner following the milking of an infected cow."
When infection is due to S aureus, treatment is altogether trickier. "Once a Staph cow, always a Staph cow." Culling could well be the answer here, especially of older animals where the infection has been present in the udder for some time, suggests Mr Edmondson.
But treatment is worth considering for first and second lactation animals, where the response is up to 60%, he says.
Response to treatment with an intramammary is poor – often less than 25% during lactation and this combined with high treatment costs makes this line of action expensive.
Best results during lactation will be using combination therapy – that is use of an intramammary tube and an antibiotic injection. Trials have shown that treatment success during lactation improves by up to 50% using this double action approach. But not with older cows, he stresses.
Dry cow therapy is more successful still, with a 60-65% cure rate achieved. "All animals must receive dry cow therapy – even first lactation heifers. The longer their udders can be kept free from S aureus the better."
But it is difficult assessing response to antibiotics, he warns. Many quarters appear to have responded initially and no bacteria are isolated from a milk sample. But when the same cow is sampled later on, bacteria may have been released from an abscess and it can be seen that the cow is still infected.
"The real concern with S aureus is that its an intermittent shedder – one individual cow cell count result wont give the true picture of whats happening – you should take three sets of results."
The third bug causing high cell counts – Strep dysgalactiae – is commonly associated with teat damage, often caused by poor machine function. Infections tend to be sub-clinical flare-ups, says Mr Edmondson. Treat cows at end of lactation with dry cow therapy and check parlour equipment.
Ideally all infected cows should be milked last to reduce the risk of cross infection to low cell count cows, he says.
Once the main type of bacteria has been identified and the necessary action taken, it will be possible to reduce herd cell counts – even to less than 150,000. "That will mean aiming for a target of 125,000, so its a lot of hard work. And there is no magic cure; unlike high TBCs or Bactoscans which can be solved rapidly, high cell counts can take up to a year to be resolved. But it is achievable provided you know what youre dealing with – remember, first know whats causing the problem."
What you should know
• Identify cause of high somatic cell count before deciding to cull cow.
• Cell count has no correlation with clinical mastitis.
• Cannot identify mastitis bugs on farm from cell counts.
• Herd cell count doesnt indicate extent of infection.
• No correlation between cell count, TBC or Bactoscan.
• Low SCCs do not increase risk of clinical mastitis.
Source: NMR, Oct 97 based on individual cell count recording of 12,000 herds in Britain.