23 February 1996

MASTITIS: FIRST KNOW ENEMY

HOW EURO RULES WILL AFFECT YOU

Producers are the key to lowering milk somatic cell counts. NI dairy company United Dairy Farmers vet

Dr Ernie Logan reports

THE new European Directive on Milk Hygiene is already in force, but will affect farmers directly from Jul 1, 1997.

The rules affect milk that is intended for human consumption and represent an increasing emphasis on herd health, housing and milking practice.

But the main impact for the producer will be the requirement to produce milk with a somatic cell count below 400,000/ml at the farm. Milk that does not reach this standard cannot be marketed for human consumption.

From this year until 1997, the UK must meet the somatic cell count standards, with samples taken from bulk loads arriving at dairy companies factories. From July 1997, however, the sampling will be taken at farm level.

Using a three-month geometric average, producers whose milk is going for manufacture or to the liquid market will have to have an SCC below 500,000 from Jul 1, 1997. But from January 1998 that figure must be below 400,000.

And after July 1997 if the geometric average exceeds the standards for any month, then the producer has a further three months to get his geometric average SCC back within the standard. If any producer has four consecutive geometric resluts above 400,000, then his milk will not be allowed to enter the human food chain and will have to be sold for other purposes or destroyed. &#42

&#8226 Test the milking machine.

&#8226 Have a good milking routine.

&#8226 Identify cows which have sub-clinical mastitis and either treat using dry cow therapy or where it has failed cull the cows.

BEFORE tackling high herd somatic cell counts it is essential to know what somatic cells are, where they come from, and why they are in the milk in large numbers.

Somatic cells are white blood cells which migrate from the blood stream into the udder in order to tackle inflammation and disease in the the udder – such as mastitis. The result of this inflammation may be a swelling of the udder and clots in the milk but very often, especially in the older cows which have some immunity, swelling and clots will not be seen. The milk will appear normal or only slightly watery at the first draw. However, a laboratory examination will show it is far from normal. In addition to the white blood cells there are also several blood proteins present.

This type of mastitis is called sub-clinical mastitis and the more cows in the herd with sub-clinical mastitis the higher will be the somatic cell count of the bulk milk. In a herd of healthy dairy cows, milked properly, the average somatic cell count should generally be under 100,000 (see Table 1).

The three key factors in high somatic cell counts are the cows, the milking machine, and by far the most important, the farmer who milks the cows.

And lowering somatic cell counts is not a one-off event but is on-going throughout the life of the herd.

The main causes of clinical mastitis and sub-clinical mastitis are germs which invade the udder through the teat canal and cause inflammation. The commonest germs causing sub-clinical mastitis are Staph aureus (84% of herds) and Strep agalactiae (13.2% of herds). These germs live mainly in the cows udder and it is the udder which is the major reservoir of infection in any herd. In addition, it has been shown in the US that in some herds milkers hands may be a significant source of Staph aureus.

Germs are passed from cow to cow at milking time by, for example, a common udder cloth, by milkers hands and by the residual contaminated milk which is left in the liners and claw piece following removal of the milking machine from an infected cow. Thus, the aim of any mastitis control scheme must be to prevent the spread from the infected cow to the younger cow with the healthy udder by establishing a very good milking routine.

Milking routine

Before milking the farmer should wash his hands. He should fore-milk each quarter to ensure the milk is normal. Fore-milking is an early warning means of identifying cows beginning to take mastitis.

Teats should be washed with running water, then dried with an individual paper towel. After milking, the teats should be immersed completely in a good teat dip either by teat dipping or spraying.

It is most important that the milking plant is operating efficiently. When there is a high somatic cell count there is a 75% chance that the milking plant will be faulty. Any malfunction will cause mechanical damage to the udder and increase the risk of invasion of the udder by germs. Common faults in the milking plant are: Too high a vacuum; vacuum fluctuation either due to poor vacuum reserves – that is the vacuum pump is too small or is inefficient, or a vacuum regulator which is insensitive; and ill-fitting liners or liners which are worn.

Unless the plant is tested and faults rectified there is no point in a mastitis control programme.

The next stage is to examine the cows to identify those which have got sub-clinical mastitis and which germ is at the root of the problem. Milk samples from each cow in the herd, either individual quarter samples or composite samples from the jar in the parlour, should be tested for somatic cell counts. Milk from cows or quarters over 200,000 cells/ml should be further examined bacteriologically to isolate the causal germs and on those germs drug sensitivity should be carried out to find out which antibiotic is the most appropriate for use in the herd.

Pinpoint subclinicals

Having identified the cows with sub-clinical mastitis, the germ involved and the drug sensitivity, how does one proceed? If the cell count is very high, immediate action may be necessary.

Cows with high cell counts which are in late lactation should be dried off immediately and the appropriate dry cow therapy used in order to cure the udder during the dry period. The cure rate will only, at best, be about 50-60% in the dry udder but this is much higher than the success rate in the milking cow, and thus I rarely advise farmers to treat milking cows. It may be necessary to withhold the milk of some of the high cell count cows and feed it to calves. Some of these cows may have to be culled at the end of their lactations especially if they have a history of several bouts of clinical mastitis in one or more quarters. Similarly, cows on whom dry cow therapy has been used, and which still have high mastitis cell counts, will have to be culled.

Initially herd somatic cell counts should be tested annually. The best time to test is when most cows in the herd are milking at peak yield and should all have low SCCs. And that mastitis programmes work is reflected in the monthly average somatic cell count of milk in Northern Ireland (see Table 2).


LOWERING THE COUNT


Table 1: Annual SCCs and TBCs (000/ml)*

12-month12-month

ave SCCave TBC

1991-92

22 herds626

Overall winner473

1992-93

26 herds638

Overall winner364

*For regional winners and runners up for high quality milk awards in 1991-92 and 1992-93.


Table 2: Monthly weighted average somatic cell count (000/ml)*

19911992199319941995

January207224207176

February251219198173

March246217202194

April224222208209

May248218208203

June270257221199

July301283252222

August316290273238

September310292265227

October256293269243208

November281265242211187

December278265220193 176

Annual average266246223201

*Milk supplied to Milk Marketing Board in Northern Ireland/United Dairy Farmers Oct 1991-Dec 1995.

Dr Ernie Logan: Lowering cell counts – not a one-off event.