agricultural production guidelines
m
Dairying in KwaZulu-Natal
Co-ordinated Extension KwaZulu-Natal Dairying 8.1 1995
MASTITIS
R F Horner & J L
Randles
Allerton Veterinary Laboratory
Clinical
mastitis
Sub-clinical mastitis
Somatic cells
Why is sub-clinical mastitis important
How
would a dairy farmer know if he has a sub-clinical mastitis problem
What should a
dairy farmer do to control sub-clinical mastitis
The word "mastitis" simply means "inflammation of the udder" and is usually caused by infection of the udder by bacteria such as Staphylococcus aureus, Streptococcus agalactiae, Strep. dysgalactiae, Strep. uberis or Escherichia coli. Mastitis may be described as peracute, acute, sub-acute or chronic according to its severity and duration. It may also be clinical or sub-clinical.
Most mastitis infections are acquired in the milking parlour during the milking procedure. The most important source of infection in the milking parlour is the cow with sub-clinical mastitis. The exceptions are the cases caused by E. coli and Strep. uberis which are regarded as "environmental" pathogens.
In the milking parlour, clinical mastitis is easily recognised by the abnormal appearance of the milk in the strip cup, and frequently by evidence of redness, pain, heat and swelling in the affected quarter or quarters.
Sub-clinical mastitis is best diagnosed in the laboratory. The udder and the milk look normal, but the somatic cell count is increased and bacteria are usually present in the milk from the affected quarter or quarters. Mastitis is a bit like an iceberg. The clinical cases are the visible tip of the iceberg, but the sub-clinical cases are that part of the iceberg which is under water and cannot be seen.
Somatic cells are white blood cells, and are part of the body's defence against bacteria or other invading micro-organisms. There are always some of these cells present, in the blood stream and in the milk, but their numbers increase significantly when infection is present.
A cow in her first lactation should have a somatic cell count of less than 100 000 per ml. Older cows should have a cell count of less than 250 000 per ml, but it may be as high as 500 000 per ml. Normal physiological fluctuations do occur during the course of a lactation.
Sub-clinical mastitis is an erosion disease. It affects the quantity and quality of milk produced and can become a source of serious economic loss to a dairy farmer if it is not adequately controlled. A cow with sub-clinical mastitis is not an economical production unit in the herd.
Milk quality is, of course, important to the consumer of milk and dairy products, and to milk purchasers who process bulk milk.
HOW WOULD A DAIRY FARMER KNOW IF HE HAS A SUB-CLINICAL MASTITIS PROBLEM?
Bulk milk somatic cell counts are a good indicator of milk quality, milk loss and the efficacy of mastitis control in the herd, as indicated in Table 1. Bulk milk somatic cell counts should be carried out on a regular monthly basis. It is a good idea to record these results on a graph in order to follow the trend. Any persistent upward trend should be investigated.
Table 1. The bulk milk somatic cell count as an indicator of lost milk production and the efficacy of mastitis control in a dairy herd
Bulk milk SCC % Lost production Interpretation < 300 000
300 000 to 500 000
500 000 to 800 000
> 800 000
0 to 2,5
2,5 to 7,5
7,5 to 15,0
15,0 to 25,0
Minimal mastitis: effective control Mastitis infection suspected
Mastitis infection present
Mastitis problem herd
WHAT SHOULD A DAIRY FARMER DO TO CONTROL SUB-CLINICAL MASTITIS?
The TWO main aims of any mastitis control programme should be:
to eliminate existing infection by treatment or culling
to prevent new infections by good dairy management, parlour hygiene, milking procedures and good milking machine maintenance and operation.
ELIMINATE EXISTING INFECTIONS
Cows with sub-clinical mastitis must first be identified so that they can be treated or eliminated from the herd. This can be done by submitting a composite (combined sample from each quarter or "cow" sample) from each cow in milk to a laboratory where a SCC (somatic cell count) and bacterial culture can be done. Because a dynamic flux exists with regard to the mastitis status of any cow (and therefore the herd), it is a good idea to do this three times, at intervals of one month, at the start of the programme.
From then on quarter samples can be collected, from the problem cows that have been identified, in order to determine the number of infected quarters. Then one will have to determine whether to treat or cull her.
It is also important to monitor the herd on a regular basis, at least every 6 months, and also to monitor the response of individual problem cows to treatment by taking quarter samples before drying off and then again about 1 month after calving.
Treatment
Treatment of sub-clinical mastitis during lactation is generally unsuccessful, and is usually recommended only in the case of a potentially good cow in her first lactation, or for very valuable, high-producing older cows.
If the somatic cell count in the bulk milk sample, on average, is less than 500 000 per ml dry cow treatment should be given at the end of lactation to all cows that have had clinical or sub-clinical mastitis during lactation (i.e. selective dry cow therapy).
If the bulk milk somatic cell count, on average, is more than 500 000 per ml, then all the cows in the herd should be given dry cow treatment at the end of their lactations (i.e. "blanket" dry cow therapy).
Cows infected with Staph. aureus should be given a second treatment about three weeks before calving, using a lactating cow remedy. Antibiotic sensitivity tests can be carried out at the laboratory to determine which antibiotics are most likely to be successful in treating infections in a particular herd.
Culling
A cow that has had clinical mastitis on more than three occasions in the course of a lactation, or that has not responded to dry cow treatment, should be put on the cull list. If only one quarter is chronically infected with S. aureus, that quarter can be "culled".
PREVENTING NEW INFECTIONS
In most cases of mastitis, the bacteria gain access to the udder through the teat canal. This can happen, either because the teat canal has been damaged in some way, or because of an extremely high bacterial challenge at the teat canal opening. The teat canal is therefore the cow's most important barrier to infection.
In order to prevent new infections in a dairy herd, it is therefore important to keep the bacterial load in the environment and on the cow's udder and teat skin as low as possible, and to prevent damage to the teat canal.
"MASTITIS IS A MANAGEMENTAL DISEASE"
Good dairy management, parlour hygiene and milking procedure, and good maintenance and operation of the milking machine, are the main ingredients of successful mastitis control.
Reducing the bacterial load in the environment and on the teat and udder skin
Common sense applies in the main
Husbandry is important in that cows kept in constantly wet, muddy "zero grazing" conditions, where dung accumulates, are more susceptible to "environmental" or "coliform" mastitis than cows kept under relatively dry, clean conditions, such as on most pastures.
Similarly, cows required to walk udder-deep through mud to reach the milking parlour, and to await milking under these same conditions, while possibly beginning to "let down" their milk, will be prone to environmental mastitis.
Once the cow is in the milking parlour, and before the attendant attaches the teat cups, it is necessary to prepare the udder for milking. Ideally, a "dry wipe" with a piece of clean, disposable paper towel to dislodge any loose dirt on the udder and teats, and to stimulate milk let-down, should be all that is necessary. If the udder is visibly dirty, the teats and the "floor" of the udder should be washed with a gentle stream of water, and then immediately dried with a clean piece of disposable paper towel which is discarded immediately. It is very important not to leave a cow standing with a drop of dirty water hanging at the end of her teat, right at the teat opening.
A high bulk milk TBC (total bacterial count) due to environmental contaminants will result if cows with dirty udders are milked without being cleaned first. If long hair is present on the udder, this hair should be clipped.
The milk from each quarter of every cow must be carefully examined by means of a strip cup, before each milking. The earlier that clinical mastitis is detected and treated, the more successful the treatment is likely to be. The strip cup with a black plastic disc is preferable to one with a mesh, as sometimes mastitic milk is only slightly watery and has no clots. Do not strip on to the floor.
The strip cup should be emptied into a suitable container, and rinsed in a sanitizing solution, after being used for a cow with clinical mastitis.
Lighting in the dairy must be good enough for milkers to be able to see the milk in the strip cup clearly.
A milker who has just handled a cow with clinical mastitis must wash his/her hands in a disinfectant solution before handling the next cow.
Work hygienically when administering any intra-mammary treatment. Clean the teat well, dip the teat, administer the remedy and dip the teat again. Do not touch the nozzle of the syringe after removing the protective cap. Do not insert the nozzle of the syringe any deeper than is necessary, to avoid damaging the tissues of the teat canal.
The order of milking is important. Cows known to be chronically infected with Staph. aureus should be milked last, and clinical mastitis cases should be milked separately, and preferably last of all.
A suitable teat dip or spray must be applied immediately the milking cluster is removed. If a teat spray is used, it is important that full coverage of the teat is achieved. Watch out for the "rain shadow" effect. Make sure the teat dip is made up to the correct strength. Do not make up large amounts at a time. Store the concentrate in a cool, dry, clean place, and keep the containers for the diluted teat dip clean.
Bacteria such as Strep. dysgalactia multiply particularly where teats are chapped or cracked. If this becomes a problem, use a teat dip containing lanolin or glycerine. If teats are particularly badly affected, apply milking salve or a suitable ointment such as "Chromasulf" after milking.
The milking cluster should be cleansed before the next cow is milked in order to remove residual milk, which may carry mastitis-causing organisms. If a backflush is used, the water should be flushed through the cluster until it runs clear. If clusters are "dunked", they must first be rinsed in a large bucket of clean water, which must be changed once it becomes too milky. Organic matter such as milk makes many disinfectants less effective. Once rinsed, the cluster can then be dipped in the sanitising agent.
The clusters should be dipped two teat cups at a time, otherwise airlocks will prevent the water or sanitising agent reaching far enough into each teat cup. Make sure the sanitising agent is made up to the correct strength.
Post-parlour feeding has several advantages, the main one being that the cow remains standing for the critical period after milking while the teat canal is closing. The post-parlour feeding area should also be clean and dry with a concrete floor, and should be roofed.
The milking parlour should be cleaned after every milking, and should be allowed to dry out as much as possible. Bacteria multiply more rapidly in moist conditions.
The milking machine should be cleaned according to the manufacturer's instructions. The correct sequence of rinsing, sanitizing, and rinsing again should be followed. Make sure that the water with the sanitizing agent reaches the correct temperature, and maintains it for the required length of time.
The milking parlour should be designed and constructed in such a way as to facilitate the entire milking procedure, and to maintain good milking hygiene. The parlour should be kept as clean as possible during the entire milking procedure.
The water supplied to the dairy should be tested once a year for bacterial quality. No coliform organisms or faecal E. coli should be present. If necessary, the water should be chlorinated. In-line chlorinators should be situated at least 100 metres from the dairy, to allow sufficient "contact time". Too much chlorine in the water may dry the teats too much. Do not forget to put in new chlorine pills when necessary.
Teat cup liners which become cracked and worn will harbour mastitis-causing bacteria. Check them regularly, and change them according to the manufacturers instructions, or earlier if necessary.
Milkers should be provided with adequate washing facilities, and should wash at least their faces, hands, and arms in a suitable disinfectant soap before each milking. Suitable protective clothing (overalls, gumboots, aprons, caps, gloves) should also be provided, and should be kept clean.
Preventing damage to the teat canal
Ramps leading into, and from the milking parlour should not be too steep, to prevent the cow from treading on a teat. Loose wire, anywhere frequented by the dairy herd could also cause teat damage.
A good milking procedure is essential if damage to the teats and teat canal is to be avoided.
Do not put on the milking clusters before the cow has been properly prepared.
Do not overmilk.
Do not "machine strip".
Close off the milking vacuum before removing the teat clusters.The milking machine should be serviced regularly, preferably every six months, but servicing alone is not sufficient. The milking machine, at all times, must be known to be functioning properly.
The vacuum pump must be adequate for the number of milking units, and there must be sufficient vacuum reserve at the end of the milking line. The vacuum regulator must be mounted vertically, and should be cleaned regularly. It should never be greased.
The vacuum gauge must be accurate, and the vacuum should be neither too high nor too low. The vacuum gauge can be checked with a simple mercury column. There should be no marked fluctuations in the milking vacuum. Fluctuations can result in "impacts" of milk, from the claw piece against the teat end, with sufficient force to drive bacteria through the teat canal. Infection can thus be spread from one quarter to another in the same cow.
The pulsators must ALL be functioning correctly, at the proper pulsation rate and ratio. If the rest phase of the pulsation cycle is not long enough, the teat will become engorged and swollen during milking, resulting in pain and discomfort to the cow. This will interfere with her milk let down. Damage to the teat canal will also result.
CONCLUSION
The secret of good management is good record keeping. Identify problem cows. Make a note of those which have clinical mastitis, and of those with sub-clinical mastitis. Record the treatment given, and monitor response to treatment.
Analyse your situation. Set attainable goals and motivate staff positively. Dairying involves team work amongst the farmer, his staff, his advisor, the veterinarian, and the veterinary laboratory. Do not hesitate to make use of professional expertise and professional services. It will pay in the long term.