Chapter seventeen
Mastitis management
T. Thirapatsakun
IntroductionAmong the challenges of dairy development in the tropics such as breeding improvement, nutrition management, control of infectious, tick-borne, blood and internal parasitic diseases, mastitis is well recognised as being a major problem as it causes a serious wastage and undesirable milk quality. When modern dairy farming in the tropics was first adopted, mastitis was foreshadowed to be an important disease in dairy cattle. Most tropical dairy farmers today have experienced disaster caused by the disease, and can no longer afford its costs in addition to their other burdens.
Control of mastitis requires understanding of its causes and of management techniques which limit the spread of infection. Since dairy farmer knowledge is often lacking help from dairy scientists, extension officers, educators and veterinarians is necessary. It is therefore important that such assistants have adequate knowledge about mastitis control.
Research knowledge regarding mastitis and its control in the tropics is limited। Knowledge from which tropical dairy industries presently benefit, largely originates from extensive research in developed countries. Although environmental and management differences exist between these systems, it is fortunate that the causative agents and infection modes are similar. Therefore, mastitis control methods are essentially similar. The same programme that is effective in pastured herds or large herds maintained in corrals can also be effective in herds located in cold climates where cows are kept in barns throughout most of the year, and in small herds in developing countries in the tropics. Programmes may be fine-tuned to suit the local needs when more locally earned specific knowledge has been accumulated through research. This chapter provides practical information about mastitis management for dairy farmers in the tropics.
What is mastitis?Mastitis is an inflammation of the udder caused by a variety of micro-organisms, mostly bacteria, that gain access to the interior of the mammary glands through the teat canal. The micro-organisms live on the cow, its udder and in its environment including the floor, faeces, soil, feedstuffs, water, plant material, and milking equipment and utensils. In response to bacterial invasion and multiplication, leukocytes move from the blood stream into milk in order to fight the infection. This constitutes the inflammatory response, which may go unnoticed in the form of subclinical mastitis, or it may be severe enough to be classified as clinical mastitis characterised by physical, chemical, and usually bacteriological changes in the milk and by pathological changes in the mammary tissue. If the infection is not contained by leukocytes or cleared through treatment, chronic mastitis may result. Such an infected quarter may lose up to 25 per cent of milk production and produce only poor quality milk as long as the infection still exists.
More than a hundred types of micro-organisms are known to cause mastitis. These organisms can be grouped as: 1) contagious bacteria: those that are spread from infected quarters to other quarters, such as, Streptococcus agalactiae and Staphylococcus aureus; 2) environmental bacteria: commonly present in the cow's environment, such as environmental streptococci and coliforms; 3) other common mastitis pathogens: such as the coagulase-negative staphylococci; and 4) uncommon micro-organisms: such as Pseudomonas aeruginosa, Nocardia, and yeasts. This distinction is of practical importance because different control measures are needed for different groups of micro-organisms. Fortunately, these organisms are normally killed by pasteurisation and thus seldom cause disease in humans unless pasteurisation is faulty or raw milk contaminated with these organisms is consumed.
Most dairy farmers are conscious of clinical mastitis in their herd, but lack a full appreciation of the prevalence and economic importance of subclinical mastitis। Clinical mastitis is easily recognised and is characterised by visible abnormalities in the udder and/or milk. The subclinical form cannot be detected by visual observation of the cow or milk but it can be identified by conducting tests to detect infecting micro-organisms or the products of inflammation such as somatic cells in milk. For each case of clinical mastitis in a herd population there will usually be 15 to 40 subclinical cases (Philpot and Nickerson 1991), and most clinical cases are preceded by infection at the subclinical level. Subclinical mastitis tends to cause a herd problem, is of long duration, reduces milk production and adversely affects the quality of the milk. It is also important because it constitutes a reservoir of mastitis organisms that may spread to other cows in the herd.
Why mastitis management?Mastitis results in decreased milk production, impairment of milk composition and quality, economic loss, and public health significance। Effectively controlling mastitis will help reverse these problems. Milk production and milk quality will be improved, producers' income will be increased, and the public hazard to health will be reduced.
Milk quality concernsGood quality milk production is one of the main objectives in dairy farming, in either large or small scale farms। This is because milk of good quality is desirable and hence saleable to the processors and acceptable by the consumers. Good quality milk and milk products as measured by consumers is wholesome, of good appearance, good predictable taste and flavour, maintaining original nutritional qualities, safe from harmful micro-organisms and substances, and has a long shelf-life. To produce good quality milk, the producers must be certain that milk comes out not only from disease-free animals but also from healthy udders by using properly sanitised equipment and maintained at its best for appearance, flavour, nutritional values, and free from drugs and chemical residues, with the least possible microbial contamination. Unhealthy udders which are mostly attributed to mastitis, regardless of the causes, definitely produce bad quality milk, either in terms of milk composition or bacterial contamination. Only sound mastitis management can help producers make more money by running, not necessarily a mastitis-free farm, but at least a near mastitis-free farm.
Effects on milk productionReduction in milk yield is an obvious symptom of clinical mastitis। During the first ten weeks of lactation it could be almost twice as much as the average of reduction throughout the whole lactation which is about six per cent (Taponen and Myllys 1995). Reduction in yield in subclinical mastitis depends on the degree of inflammation which can be estimated from the somatic cell count in milk. Significant losses from individual cows and herds have been shown to be associated with elevated somatic cell counts; higher count equals greater loss. The loss of an individual cow increases from six to 30 per cent as cell counts increase from 100,000 to 1,600,000 cells/ml while the loss of the entire herd increases from six to 29 per cent for cell counts from 500,000 to 1,500,000 cells/ml (Philpot and Nickerson 1991).
Effects on milk compositionSomatic cell count also reflects the changes which occur in the composition of milk। As the degree of inflammation increases, the chemical composition of milk more closely approaches that of blood because the components filter from the blood circulation into the mammary gland. Table 17.1 shows the effect of subclinical mastitis on various milk components. It indicates that the yield of total solids, butter fat, solids-non-fat, casein and lactose is reduced substantially while total protein changes only slightly.
Economic importanceMastitis causes economic losses from decreased milk production and increased management costs. Losses from mastitis are twice as much as losses from infertility and reproductive diseases. The largest proportion of the losses results from a direct drop in milk revenues, the non-marketable milk contaminated with antibiotics, decreased milk production which invariably accompanies the infection and premature culling of the animal in many instances. In Thailand, a rough estimate of the annual loss in 1989 was 700 million baht (Thirapatsakun 1989) and in 1998 the annual loss of 1500-2000 million baht is quite probable. This figure is substantiated by an 18 million baht cost of mastitis tubes imported annually.
Losses caused by clinical mastitis include; discarded milk with antibiotic residues; drug and veterinary and possibly laboratory costs; the possible death of an infected animal; culling; udder damage and interruption of breeding improvement programmes.
A formula for calculation of the basic loss due to clinical mastitis per cow has been developed (Thirapatsakun 1989) as follows:
Em = [P + (L x Kg x B)] M/4where:Em = loss due to clinical mastitisP = cow's priceL = days no milk deliveredKg = average daily milk productionB = price per kg raw milkM = no. of affected quarter(s)
If a cow valued at 28,000 baht, with 300 days in milk, and an average milk production of 10 kg/day at the price 9।00 baht/kg, lost one quarter permanently from mastitis, the overall loss per lactation would be 13,750 baht. The loss would also be 27,500, 41,250 and 55,000 baht for loss of 2, 3 and 4 quarters, respectively.
Therefore a cost of 2000 baht overall results from a cow with an average 10 kg daily milk yield and one quarter affected with a mild form of mastitis, needing three day treatment, milk withheld for seven days from 4 quarters costing 200 baht for bacterial culture and sensitivity test, 240 baht for mastitis tubes (40 x 6; baht x milkings), 50 baht for systemic injection, 9.00 baht/kg raw milk price, and 300 baht for miscellaneous expenses, for example, petrol or vet fees.
Much has been said about economic losses due to clinical mastitis. However, the loss which is less obvious but even larger and higher in frequency, is the loss in milk yield and its quality caused by subclinical mastitis. In Thailand, for example, with the recent average figure of somatic cell counts from 800,000 to 1,000,000 cells/ml (Sukrawee personal communication), the estimated loss of 18 per cent (Philpot and Nickerson 1991) based on 1993 national milk production (232,760 ton) onward due to subclinical mastitis would be approximately 3,500,000 baht which would increase along with 17 per cent increase of milk production annually (MAAC 1997).
Public health significanceMastitic milk can also pose a threat to human health. With severe clinical mastitis, gross abnormalities of milk are readily observed and milk is discarded by the producers. Such milk normally would not enter the food chain. But with subclinical mastitic milk or in the case of a small amount of badly infected mastitic milk accidentally mixed into bulk milk, changes in milk may be visible. Some mastitic milk carries bacteria that can cause severe human illness. Although pasteurisation is likely to destroy all human pathogens, there is concern when raw milk is consumed or when pasteurisation is faulty. Some strains of Staphylococcus aureus may produce heat-resistant enterotoxins which cause serious food poisoning.
Another public health concern regarding mastitis is antibiotic residues in milk. Residues in foods can initiate severe reactions in people allergic to antibiotics and, at low levels, can cause sensitisation of normal individuals and development of antibiotic-resistant strains of bacteria. Compliance with recommended withholding time helps minimise the risk of antibiotic residues in milk and meat which is the producers' responsibility.
How does mastitis occur?Mastitis may be attributed to deficient management, improper milking procedures, faulty milking equipment, inadequate housing and breeding for ever-increasing milk yield. Management and environmental factors also interact, increasing the exposure of cows to mastitis organisms, reducing the cow's natural resistance to the disease, or aiding micro-organisms' entry through the teat canal. Climate, season, herd size, type of housing, nutrition and stress all influence the incidence of mastitis. Additionally, these factors interact with genetic and physiological factors such as stage of lactation, milk yield, milk flow rate, and pregnancy. Management and environmental factors in the majority of dairy farms in the tropics are far from adequate in terms of mastitis control. Control on smaller farms should be no more difficult to control than the larger ones. Cows anywhere in the world rely upon keen observation by owners and herdsmen to maintain management at a high level.
Detection of mastitisMany different cowside and laboratory tests can be used to detect the presence of mastitis.
Physical examinationThe most frequently used test involves physical examination of the udder. This is accomplished when the udder is being prepared for milking. Quarters that are hot and enlarged will be evident. Thorough examination is best carried out after milking.
Strip testThe second most frequently used test is the strip test, which involves stripping the first few streams of milk onto a strip plate or onto the floor in milking parlors. Mastitic milk will show discoloration, clots, or other abnormalities. Milk should never be stripped directly into the hands, nor should it be stripped onto the floor of a stanchion barn where the cows lie at the same place they are milked, as this procedure will aid in the spread of mastitis organisms to other cows or the other quarters. The strip test should be used by dairy farmers prior to each milking to aid in detecting clinical mastitis. Removal of the first milk also stimulates milk let down and shortens the milking period.
Paddle test to detect somatic cellsThe California Mastitis Test (CMT) and other similar tests are useful in detecting abnormal milk. These tests are basically management tools to aid in identifying cows that may require special attention. The test reagent reacts with somatic cells in milk to form a gel. Reactions are scored according to the amount of gel formed when milk is mixed with the reagent. Many dairy farmers and veterinarians prefer to use a simplified scoring system as follows: N = Negative (no gelling), S = Suspicious (some gelling), and P = Positive (distinct gelling) (NMC 1987).
A few streams of milk should be discarded before the test is conducted, and results should be recorded for future reference; gel formation is very short lived. The paddle must be rotated gently in a horizontal plane and all reactions read within five to 10 seconds after rotation of the paddle has begun. When this is done, the test is valuable in detecting subclinical infection that might otherwise go undetected. Positive reactions do not always indicate the presence of infection, and therapy should never be initiated solely on the basis of such results.
Laboratory testsVarious inflammatory mediators such as somatic cells, serum proteins, enzymes such as NAGase (N-acetyl-_-D-glucosaminidase), and sodium and chloride concentrations may be tested for mastitis, especially the subclinical form. However, one should be extremely cautious comparing results from different materials as the changes in the inflammatory parameters do not necessarily parallel during the course of the inflammatory process. The most accurate way to identify infected cows is to aseptically collect milk samples from individual quarters or composite samples from all four quarters and have them cultured in a laboratory that specialises in mastitis microbiology.
Collection of milk samplesThe reliability of laboratory culturing is dependent upon the manner in which milk samples are collected, stored, and handled afterward. Milk sample collection should be done aseptically so that the sample contains only pathogenic bacteria derived from the milk compartment of the udder, not from the teat skin or surrounding regions. When quarter milk samples are taken, two or three streams of milk should be discarded, and the teat end scrubbed for a few seconds with cotton balls moistened with 70 per cent alcohol prior to collecting the samples. Teats on the far side of the udder should be sanitised first and near teats last to avoid the latter being touched again by hands or forearms after being sanitised if the far sided teats were to be sanitised last. When teat ends are dry, milk samples should be collected in prelabelled sterile test tubes and closed with caps from near teats first and far teats last and put on ice water or refrigerated until delivered to the laboratory. Milk samples should not be frozen if the somatic cell counting is to be conducted as this destroys the somatic cells.
Natural defence mechanismsNatural defence mechanisms of the udder can be used to our advantage in mastitis control.
Teat sphincter and keratinThe first barrier against mastitis-causing organisms is the tissues surrounding the teat canal, particularly the sphincter muscle that keeps the canal closed between milkings. Since the teat canal remains partially dilated for up to two hours after milking, it is recommended that cows be fed at this time to keep them on their feet until the sphincter muscle tightens to reduce the size of the opening. Antibacterial protein and fatty acids containing keratin in the teat canal partially blocks the opening in healthy teats.
Somatic cellsOnce micro-organisms penetrate the teat canal, the next line of defence encountered is somatic cells in milk. Somatic cells are present at low levels in the absence of infection but rise dramatically when a quarter becomes infected. Approximately 99 per cent are white blood cells. The function of white blood cells is to destroy infecting micro-organisms and to aid in repair of damaged tissue. The other one per cent of cells in milk come from damaged milk-secreting tissues.
Developing countries in the tropics can hardly afford the monthly electronic somatic cell counts used in developed countries. However, other cheaper but less accurate indirect tests for somatic cell counts such as the California Mastitis Test (CMT) or Wisconsin Mastitis Test (WMT) should be used. Above all, emphasis should be made on preventing the entry of micro-organisms into the teal canal by good hygiene and good milking technique.
AntibodiesAntibodies are a very important resistance mechanism because they are specifically directed against certain mastitis causing bacteria, and their concentrations can be increased by vaccination. However, as many different species of bacteria can cause mastitis and most bacterial species that cause mastitis include many immunologically different strains, vaccination against mastitis is rather difficult. Vaccination programmes for controlling mastitis in the tropics have not yet been attempted.
NutritionMalnutrition increases susceptibility to infections. As dairy cows are bred to produce more milk, it is difficult to fulfil the nutrition requirements to cope with the production. Marginal nutritional deficiencies are likely to occur. Cows with parturient paresis (milk fever) and ketosis (energy deficiency) or selenium, vitamin E, and copper deficiency have an increased risk of mastitis. Vitamin A and beta-carotene are also needed for the mammary immune system to function properly (Chew 1987).
Control of mastitisBackground problemTropical dairy farmers, unaccustomed to paying much attention to the mammary glands, often thought that mastitis would never occur in their farms. However, commercially raising of dairy cattle highlighted the disease. Mastitis management becomes more difficult when some dairy farmers, embarrassed by their knowledge and management deficiency, disguise the truth about the real incidence of mastitis in their herd. The situation is aggravated by inadequate milk tests at reception of the majority of the milk collecting centres.
Many dairy farmers appear hesitant to implement mastitis control programmes because of the inconspicuous nature of the disease and the fact that most are accustomed to living with it. Tropical dairy farmers will have to pay more attention to all the factors associated with teat exposure and resistance to micro-organisms, both during intervals between milkings and at milking time. These factors include housing management, hygiene, nutrition, and stage of lactation, as well as methods used in milk production such as premilking udder preparation, proper milking equipment and technique, and postmilking management, particularly when milking is performed in the same place where the cows live such as in the stanchion barns.
Advisory personnel or extension officers must be equipped with sound knowledge about the disease, having correct understanding about the disease and its control. Furthermore leaders in the dairy industry should agree on common goals and recommendations, and ensure that everyone associated with the dairy industry makes the same recommendations. Otherwise farmers are likely to become confused and may not adopt any new practices.
Mastitis control strategyMastitis is best viewed as a herd problem rather than an individual cow problem. Unlike other cattle diseases such as brucellosis or tuberculosis, mastitis cannot possibly be eradicated on a large scale. Each individual herd is the unit of control by itself. The level of mastitis in a herd has nothing to do with the level in neighbouring herds. In controlling mastitis on a large scale, the primary need is not for a national mastitis control programme but for a herd mastitis management programme applied nationally.
Controlling mastitis involves a number of steps referred to as a `control programme'. To be acceptable, such a programme must be practical, easy to understand, highly effective in most dairy herds, increase economical returns, reduce new infection, shorten duration of pre-existing infections, provide tangible evidence that clinical mastitis is reduced, and be subject to easy modification as improved methods are developed.
In controlling mastitis, it is necessary that the level of infection in a herd be known to be able to assess seriousness, and sources and risk of spread of the infection. Prevalence of mastitis indicates a level of infection or the proportion of cows or quarters infected with the disease at a given time. The level of infection, clinical or subclinical, varies from farm to farm according to the environment and management factors in each herd. Regular monitoring of each farm is necessary. For practical reasons, the effectiveness of a mastitis control programme is measured by the level of infection, that is, the percent of cows or quarters infected which is dependent upon both the rate of new infections and the duration of each infection. If the rate of infection is reduced, the level of infection will fall, though very slowly. If the duration of infection is effectively shortened, the level of infection will soon be reduced, provided that no new infections occur. To keep mastitis at a low level it is necessary to prevent as many new infections as possible and then shorten the duration of those that do occur and finally eliminate the existing infection.The Comprehensive Plan of Mastitis Control, designed to reduce the rate of new infections and shorten the duration of infection (Philpot and Nickerson 1991), has been widely adopted and if followed conscientiously on a continuing basis can effectively control mastitis in the vast majority of dairy herds. With some modification, it should be appropriate to apply for mastitis control in tropic
Recommended milking proceduresAlthough the cow is usually exposed to the act of milking and associated events for less than 15 minutes a day, this period is a prime time for increased susceptibility to new infections. Correct milking procedures therefore are important, regardless of whether cows are milked by hand in traditional dairying situations or with modern milking machines. Preparation of teats and udders for milking reduces the number of contaminating micro-organisms on teat skin, and stimulates milk let down. Correct teat and udder preparation will reduce microbial contamination of milk, decrease residual milk left in the udder at the end of milking, increase milk yield, decrease milking time, and reduce the spread of contagious and environmental organisms that may cause mastitis and/or reduce milk quality. A summary of recommended milking procedures is as follows:
Provide cows with a clean, stress-free environment
The cows should be milked in an environment that is as clean and sanitary as practical. The milking time should be a consistent routine, and the cow should not be frightened or excited before milking because such stress results in hormones being released into the bloodstream that interfere with normal milk let down and may reduce the cow's natural resistance to diseases such as mastitis.
Crossbred cows that have hairy udders should be clipped as necessary to remove long hair and to reduce the amount of dirt, manure and bedding that may contaminate milk. Also, the hands of milkers should be thoroughly washed and dried before milking, and hands should be rinsed in a disinfectant solution between cows. This procedure will help to minimise the spread of mastitis organisms from cow to cow.
Check udder and foremilk for mastitis
The presence of clinical mastitis can be detected by using the hand to physically examine the udder and by using a strip cup or plate to examine foremilk before each milking. These procedures aid in detecting hot, hard, and enlarged quarters as well as clotty, stringy, or watery milk. Strip cups and plates should be cleaned and sanitised after each milking to prevent the spread of mastitis organisms. Milk should never be stripped directly into the hand because the procedure spreads organisms from teat to teat and cow to cow.
Wash teats and lower surface of the udder
Correct washing and massaging of the udder sends a signal to the pituitary gland at the base of the brain, which secretes the milk let down hormone, oxytocin, to the bloodstream. This hormone then travels to the udder where it stimulates the muscle cells surrounding milk-secreting tissues to contract and cause milk let down. All teats, as well as the lower udder, should be thoroughly washed, massaged, and dried.
A sanitising solution should be used in a bucket with an individual cloth or paper towel to wash the udder when cows are maintained in stanchion barns. Use of a common cloth or sponge should be avoided because these become grossly contaminated and are almost impossible to sterilise.
Use a premilking teat dip (optional)
Disinfecting teats with a germicidal teat dip before milking is known as predipping; this can reduce the rate of infection with environmental organisms by 50 per cent and a modest reduction in mastitis caused by contagious micro-organisms. The recommended procedure is to: clean teats, forestrip, predip all teats, wait 20 to 30 seconds for contact time, and thoroughly dry the teats with individual towels to remove germicide residues before applying milking caps.
Dry teat thoroughly
Regardless of method used to wash teats and the ventral surface of the udder, it is imperative that surfaces be dried. Single service paper towels are preferred, though individual cloths for each cow can be used if they are washed, sanitised, and dried between milkings. Use of excessive water to wash teats and udders and failure to thoroughly dry the skin, results in water laden with micro-organisms draining down and being drawn into teat cups.
Attach teat cups within one minute
Attachment should be done carefully to prevent the entrance of excessive air into the milking system. Maximum internal udder pressure is reached approximately one minute after udder preparation has begun and lasts for about five minutes. Since the majority of cows will milk out in three to five minutes, attachment of teat cups one minute after stimulation has begun makes maximum use of the milk let down hormone oxytocin.
Adjust milking units
Milking units should be observed closely while attached to the udder to insure that they are adjusted correctly and to aid in preventing liner slips. It is extremely important that slipping or squawking teat cups be minimised because such occurrences slow down the milking operation and may cause machine-induced infections. If liner slips occur at the same time the liner opens, tiny droplets of milk may be propelled against the end of the teat at high velocity. Such droplets may contain mastitis organisms and may penetrate the teat canal. Since milk flow is reduced near the end of milking when most liner slips occur, the chances of the organisms being flushed out are reduced and an infection of the quarter may result.
Shut off vacuum before removing teat cups
The vacuum should always be shut off before teat cups are removed at the end of milking. Never pull the milking unit off the udder while still under vacuum because this practice causes the same problem as squawking teat cup liners and may result in machine-induced infections. A minute or two of overmilking with a properly functioning milking unit does not pose a major risk in terms of mastitis. If a quarter milks out ahead of the other quarters and if the teat cup remains attached to the teat without slipping, it should be left on because careless removal may permit air to enter, which stimulates a linerslip and may result in machine-induced infection via droplet impaction. If there is a probability of slipping on a particular teat, then the cluster should be lifted gently to seal the short milk tube of the liner over the ferrule of the claw to shut off the vacuum before detachment from the teat. Never remove the teat cup while under vacuum.
Dip teats with an effective teat dip
The dipping of teats immediately after milking in a safe and effective teat dip is the most important thing a dairy farmer can do to reduce the incidence the rate of new infections. The goal should be to dip the entire surface of the teat that comes into direct contact with the teat cup liner. This postdipping is to aid in controlling contagious mastitis. Teat spraying almost never covers the entire surface of the teat and is not encouraged. Teat cups should be kept clean and sanitary, but teat dip should never be poured back into the original container as the strength of the used teat dip may be reduced and allow the organisms to survive.
Disinfect teat cups between cows (optional)
Teat cup liners are often heavily contaminated with mastitis organisms as a result of milking infected cows and may serve to spread organisms from one cow to another. If the liners are to be disinfected, two teat cups should be dipped at a time, in a disinfectant solution. The solution should be changed when it becomes cloudy. This procedure must be done properly otherwise it may serve to spread mastitis organisms rather than eliminate them.
Recommendations for milking equipmentProblems with both milk quality and mastitis can result from improper design, malfunctioning, misused, or an improperly cleaned milking machine. Research in Denmark shows that if milking machines are properly designed, maintained, and used they will account for only about six per cent of all infections of the udder (Philpot and Nickerson 1991).
Milking systems are available in many different designs and sizes to meet the needs and resources of individual dairy farmers. All milking systems have the same basic components. These include: a vacuum system; pulsation system; milk removal system; milk handling system; and an electrical system. With respect to mastitis control, it is the milk removal system and in particular the teat cup liner slips which are associated with milking machine induced infections. Recent research has shown that a problem with liner slips exists if there are more than five to 10 liner slips per 100 cows. Some of the causes have been shown to be: poor cluster alignment; poor liner design; uneven weight distribution cluster; blocked air vent at the claw; and flooded milk lines. Other research has shown that slipping or squawking liners result from interaction of: liner design; cluster weight; vacuum levels; vacuum fluctuations; milking wet teats; absence of hose support arms; overmilking; and teat size.
Control of contagious mastitisThe most important contagious organisms are Staphylococcus aureus and Streptococcus agalactiae, though Corynebacterium bovis is also common in many dairy herds. Mycoplasma bovis is also highly contagious, but is very rare. The primary reservoirs for these organisms is infected quarters, though Staphylococcus aureus readily colonises teat skin and the teat canal, and has also been isolated from the udders of heifers that have never calved. These organisms, with the exception of Mycoplasma, are usually controlled quite easily by: good udder hygiene; correct use of good milking machines; dipping teats after milking; and treatment of all quarters of all cows at drying off.
The spread of Staphylococcus aureus within a dairy herd can be reduced by: milking first lactation animals before older cows; uninfected cows second; and known infected cows last. The use of vaccines against this organism should be viewed as an adjunct to control programmes described above, rather than as a replacement.
Streptococcus agalactiae can be eradicated from a dairy herd within a few months by following a culture and treat programme followed by the `Comprehensive plan of mastitis control' outlined earlier. It is also necessary, that the situation be evaluated by a qualified person prior to detailed procedures for eradicating the micro-organism being implemented.
Control of environmental mastitisA wide variety of environmental pathogens may cause mastitis. The most important organisms in this group are Streptococcus uberis, Streptococcus dysgalactiae and coliforms such as Escherichia coli and Klebsiella spp. As the name implies, these organisms originate from the environment and control is best achieved by decreasing exposure of the teats to the organisms. This means keeping cows in as clean an environment as possible. Infection with these organisms is higher in housed herds than in pastured herds, when muddy conditions exist, and during the wet season. Organic bedding such as straw, supports the growth of environmental bacteria more than inorganic bedding such as sand or limestone.
Environmental mastitis is associated with a high incidence of clinical mastitis in the herd which may fluctuate according to season. The bacteria isolated from the clinical cases are usually gram negative or Streptococcus uberis. If the mastitis is generally caused by E. coli, sampling of the whole herd is not necessarily of much help, as cases of E. coli mastitis seldom become chronic. The key to solving an E. coli mastitis problem is usually a dry environment. Water use should be kept to a minimum in the barn. Teat dipping and dry cow treatment have no influence on coliform mastitis.
Streptococcus uberis infections often occur during the dry period. The sources of infection are generally the cow and its immediate environment. Antibiotic treatment is not always efficient and chronic cases must therefore be culled. Good hygiene is most essential in the prevention of Streptococcus uberis mastitis.
Klebsiella infections are typically very difficult to treat, and the infected animals usually have to be culled. Before the mastitis problem is found to be caused by Klebsiella, a few cows may already have been lost. A vaccine against coliform mastitis is commercially available in some countries. A heat-killed Escherichia coli J-5 mutant vaccine tested at the University of California, Davis administered subcutaneously at drying off, 30 days later, and again within 14 days of calving can uniquely stimulate antibody production against a wide variety of coliform bacteria, such as Escherichia coli, Klebsiella pneumoniae, and Enterobacter species. The vaccine alone will not eliminate coliform infections from a herd, but if combined with good management practices, will reduce the incidence of new infection.
Control of mastitis caused by other micro-organismsThe opportunistic micro-organisms include over 20 species of Staphylococcus species other than S. aureus (sometimes referred to as coagulase-negative-staphylococci or CNS) and are often the most frequently isolated bacteria in the herd. Infections with these organisms are usually mild and elicit only a slight increase in somatic cell count. The organisms are normally found on healthy teat skin and on the milkers' hands and are thus in an opportunistic position to colonise the teat canal and penetrate to the milk-producing tissues of the udder. Incidence of staphylococcal infections is greatest during the early dry period when the teat skin is not exposed to germicides, so the percentage of quarters infected is high at calving. The use of a postmilking teat dip is the best means of controlling infections by Staphylococcus species. Dry cow therapy will eliminate a high proportion of existing infections at the end of lactation, but new infections in the dry period can be expected.
Other, less common, organisms that may cause mastitis include Pseudomonas aeruginosa, Arcano pyogenes (formerly known as Corynebacterium pyogenes and Actinomyces pyogenes), Nocardia asteroides, Serratia marcescens, Prototheca zopfii, Candida (yeast), and Bacillus spp। Infections by these organisms are usually sporadic and affect only one or a few cows in a herd, but can produce severe clinical symptoms. Pseudomanas aeruginosa, Serratia marcescens, and Nocardia asteroides are generally resistant to most antibiotics and can survive in certain teat dips. Herd outbreaks with these micro-organisms are usually traced to contaminated water and poor treatment practices. The organisms are inadvertently placed into an udder by contaminated cannula, syringes, treatment preparation, home-prepared medications and inadequate pretreatment teat end sanitation. Water sources and udder wash hoses should be checked. Milking equipment should be kept in good order and teat end injury should be avoided as lesions provide a site for the growth of all mastitis micro-organisms.
Role of mastitis therapyDespite the use of excellent preventive methods, some new infections still occur। Spontaneous recovery may occur in mild cases while others may require drug therapy. Culling, the other viable alternative for eliminating existing infections, is necessary in the cases of chronic infections that have resisted therapy. Successful antibiotic therapy for intramammary infections involves: drugs reaching all sites of infection in the affected quarters; drugs remaining at adequate therapeutic levels at all sites of infection for an adequate period of time, and killing all infecting micro-organisms.
Lactation therapy
Treatment during lactation is indicated only when: cows are infected with Streptococcus agalactiae; the herd somatic cell count is 600,000, and when clinical mastitis is present. Cure rates of the treatment depend on types and drug sensitivity of the infecting micro-organisms, and the intramammary conditions. It is advisable that treatment protocol be designed by a consulting veterinarian who will base selection on previous experience in the herd and on clinical signs and environmental circumstances. Drugs should be chosen according to the results from bacteriological diagnoses and sensitivity tests. Response to mastitis treatment should be monitored using appropriate inflammatory indicators such as changes in somatic cell count, protein, enzyme and electrolyte contents of milk. The California Mastitis Test (CMT) which measures the somatic cell count of milk is a simple test that the dairy farmers can also use. The test is rather subjective but its reliability is improved when quarters are compared. One should be aware of possible transmission of infection to other cows or quarters.
In the case of cows that are acutely ill, it may be necessary to administer; milk let down hormone oxytocin; large volumes of electrolytes; products to counteract inflammatory prostaglandins, and other drugs as directed by the herd veterinarian. Frequent milking out of the udder may also aid the animal in recovery because this practice helps to remove infecting organisms and their toxins and rid the udder of cellular debris.
Combination therapy, the procedures in which cows are treated simultaneously in the udder as well as systemically with compatible drugs may result in a significant increase in the concentration of antibiotics in udder tissues than treatment in the quarter alone, thus permitting drugs to reach micro-infections deep within the tissues। Cure rates against the chronic cases can be doubled.
Dry cow therapy
Dry cow therapy is the treatment of the udder with intramammary antibiotics at the end of the lactation. Treatment of all quarters of all cows at drying off with long-acting antibiotics is one of the most important components of the `Comprehensive plan for mastitis control'. It is the preferred time to treat subclinical infections. Advantages of dry cow therapy include: the cure rate is higher than when treated during lactation; higher concentrations of long-acting antibiotics can be used safely; the incidence of new infections during the dry period is reduced; damaged tissue is allowed to be repaired or redeveloped before freshening; clinical mastitis at freshening is reduced, and drug residues in milk are avoided. Infected quarters treated at drying off and cured at calving will produce 90 per cent of potential milk production during the next lactation whereas a quarter becoming infected during the dry period or which remains infected from the previous lactation will produce 30 to 40 per cent less milk. Concern about the possibility of routine dry cow therapy increasing the resistance of mastitis micro-organisms to commonly used drugs can be relieved since widespread use of dry cow therapy for more than 25 years showed no evidence of treatment associated resistance to drugs among major or minor mastitis pathogens (Philpot 1997).
The recommended procedure for dry cows is to: bring the cow to the end of lactation; treat in all quarters following the last milking; and reduce energy intake। Udders will fill with milk until a certain hydrostatic pressure level is reached and the milk will then be reabsorbed into the bloodstream. Milk in the udder at drying off is the useful vehicle for transporting drugs to all infected sites throughout the udder. Thus, the cow should not be completely dry when treatments are administered.
Treatment procedures
Regardless of the type of treatment used, it is important to follow label directions precisely to avoid drug residues in milk. Treated animals should be clearly identified in some obvious manner and they should be kept separate from untreated animals to aid in preventing their milk from being mixed with milk from untreated animals.
Prior to administering any type of therapy into a quarter, it is imperative that teat ends be thoroughly disinfected by swabbing for a few seconds with a pledget moistened with 70 per cent alcohol. Another procedure that is used by many veterinarians is to dip the teat prior to treatment with a teat dip and then administer the treatment through the dip. If teats are not sanitised before treatment, micro-organisms present on the end of the teat and in the teat canal may be forced into the quarter and may cause more severe mastitis than the one for which the antibiotic was intended.
The method of infusing drugs into the udder is also critically important। For example, forcing cannula all the way through the teat canal may actually force micro-organisms into the quarter. Insertion of the infusion cannula about three millimetres into the teat canal, increases the cure rate and reduces new infection. Most pharmaceutical companies have now designed infusion cannulas to this specification.
Avoiding drug residues
To avoid detectable residues in milk it is imperative that label instructions be followed exactly। Special attention should be given to dose levels, routes of administration and withdrawal time. Intramuscular injections, uterine boluses, and antibiotic feed may also produce antibiotic residues in milk with even longer withdrawal period, apart from intramammary infusion. Treated cows should be kept separate and should be clearly marked. Written records should also be kept of all treated cows as this information can help in making cull decisions with chronic cases. Treated animals must not be sold for slaughter until the drug withdrawal time for meat has elapsed.
Handling mastitis problem herdsA mastitis problem herd may have a high rate of clinical mastitis, a high somatic cell count indicating a herd problem of subclinical mastitis, a high bacteria count or a combination of the above. Poor milking hygiene, poor environmental hygiene, malfunctioning milking machines, improper milking procedures, and inadequate treatment methods are some of the usual reasons for mastitis problem herds.
The best way to start with a problem herd is by analysing a sample of herd milk in the laboratory, employing the recommended procedure (Philpot and Nickerson 1991) which has now been widely adopted. The procedure provides valuable and rapid information about the udder health and hygiene of milk production of an individual herd. The procedure involves three tests: a somatic cell count; a bacterial count (standard plate count), and microbiological culturing on blood agar to identify the types and numbers of different micro-organisms in the sample. Integration of the information obtained from the three tests can then be evaluated by a veterinarian or a trained technician to determine the nature, extent, and likely cause of a herd mastitis problem, and identify a herd hygiene problem as evidenced by improperly cleaned milking equipment, wet milking, contaminated water or poor cooling of milk. The information becomes basically a road map for determining the corrective action that should be taken.
Any herd with a high somatic cell count (500,000-1,000,000) should be considered a problem herd because mastitis will be prevalent. A few streams of foremilk from each quarter should be examined carefully to detect abnormalities. Cows with milk that is visibly abnormal or positive to the CMT should be segregated and the milk withheld from the bulk tank. The quarter milk should also be submitted for somatic cell count and cultured in the laboratory to identify the micro-organism responsible for the infections. This information is valuable for determining whether to treat or cull affected animals, and may help in determining the source of the problems as well as the corrective actions that should be undertaken.
High bacterial count indicates probable existence of mastitis-causing micro-organisms and/or bacterial contamination caused by poor milking hygiene, faulty cleaning or functioning of milking machine, and/or poor cooling of milk. If the number of streptococcal organisms is more than 75 per cent of the total, the source is likely to be infected udders. If the streptococcal count is less than 25 per cent of the total, the cause is likely to be improperly cleaned milking equipment, poor udder preparation (wet milking), or poor cooling of milk (Philpot 1997).
Samples with large numbers of streptococcal bacteria plus large numbers of staphylococci, coliforms, spore formers, and other micro-organisms often indicate a dual problem of infected cows and poor udder preparation (wet milking). A sample with very high staphylococci usually indicates poor cooling of the milk. High staphylococcal counts in herd milk are rarely, if ever, caused by an infected udder alone (Philpot 1997).
High coliform counts often indicate broken teat cup liners, low water temperature when the milking system is washed, milkstone on milk-contact surfaces, and failure to use correct chemicals to clean and sanitise milking equipment. A sample with large numbers of coliforms, staphylococci, and environmental streptococci often indicates faulty cooling of milk.
Above all, the `Comprehensive plan of mastitis control' complemented with the Recommended Milking Procedures outlined earlier are the best set of guidelines for control of mastitis.
Mastitis control in heifersUdder infections among heifers are quite prevalent, even in very young animals and can cause inflammation and tissue damage prior to calving.
Sources of infecting micro-organisms are believed to be: the environment; insects, especially flies; suckling among calves (particularly those fed mastitic milk); and microflora in the mouth and on the skin and haircoat. Management practices such as fly control, using individual calf pens, segregation of pregnant heifers from dry cows can help preventing development of mastitis in heifers.
Strategically treating pregnant heifers with antibiotics at different stages prior to first parturition, reduces prevalence of mastitis during early lactation। In instances where heifers are known to harbour udder infections caused by Staphylococcus aureus, they should be treated at about eight to 10 weeks prior to calving with a dry cow treatment product. With other types of infections, the preferred strategy is to treat at about seven to 10 days before the expected calving date with a lactating cow product. This practice will eliminate approximately 90 per cent of the infections. Treated heifers will produce 10 per cent more milk than untreated heifers. Extreme caution must be exercised when treating heifers to make certain that teat ends are thoroughly sanitised prior to treatment, and that insertion of the teat cannula is partial.
Implementing herd mastitis controlAn effective mastitis control programme should be carried out, ideally by a team of veterinarians, laboratory microbiologists, milk plant field representatives or extension officers, milking equipment dealers, and most importantly, the dairy farmers। Extension officers are mainly concerned with environmental aspects and milking techniques and often take milk samples to the laboratory for mastitis diagnosis. Milking equipment dealers should ensure that the machine is properly cleaned, maintained and functioning adequately. The programme should be formulated by the practising veterinarian. Advice and education should be focussed on the dairy farmers who must be enthusiastic and well motivated to ensure the success of the programme.
Establishing goals
In the beginning, goals should be realistic and achievable. Higher goals can subsequently be attempted when some confidence is gained. The suggested criteria used for assessing the extent of mastitis problems include: herd milk somatic cell counts; herd milk bacteria counts; proportion of the individual cows with subclinical and clinical infections, and; discarded milk due to clinical mastitis both in terms of percentage of the production and the revenue lost. Ideally an electronic cell counter should be used for somatic cell counting. If this is not available, use of WMT or milk NAGase activity should be encouraged for indirect somatic cell count estimation.
High incidence of clinical mastitis usually results from a major deficiency in management such as an unsanitary milking area, inadequate milking hygiene, faulty milking machine, or purchase of infected cows. Any herd with a somatic cell count above 500,000 is usually considered as a problem herd.
While goals used in developed countries (Table 17।3) are probably unrealistic for most of the tropical dairy herds, they provide an example for long term goals.
Steps in the control programme
Initial evaluation of the mastitis situation in the herd should be measured by; interviewing the farmer and taking notes; evaluating the state of health of the whole herd; general herd management including, types of housing, bedding, feeding, manure removal, temperature and humidity; age or parity distribution of cows; milking equipment evaluation including rubberware use; milking practices and hygiene; mastitis treatment; culling rate and reasons; bulk milk cell count, followed by individual cow cell count or individual quarter cell count or equivalent estimates by CMT or WMT or NAGase activity; and existing bacteriological diagnosis from the laboratories।
When infection prevalence for a herd is determined, attention must be paid to the quality of the microbiological samples. Aseptically taking of quarter samples from the whole herd is a laborious operation. Sampling should thus be planned and care exercised when sending the samples with necessary information to the laboratory. To cut costs, the microbiological examination may be conducted only on those quarters, which are inflamed. Dry and periparturient heifers may be included in the study for more reliable results. At pre and post partum, the values of the inflammation indicators are always high and comparison of the quarters is then critical.
Disagreements between bacteriological tests and tests detecting inflammatory changes in milk are often encountered. Several reasons for these include: antibacterial factors in milk which prevent outgrowth of bacteria; there are so few bacteria that they cannot be isolated in the small volume cultured; the laboratory methods are not relevant for all types of microbes associated with mastitis; the inflammation is caused by udder trauma or teat injuries; the bacteria have died but the toxins released from them maintain the inflammatory response, and/or inflammatory reaction disappears more slowly after bacteria have been eliminated.
The results from the initial evaluation of mastitis situation should reveal whether the mastitis is environmental or contagious. Appropriate sanitation measured described earlier should then be applied accordingly. The producers must be realise that evidence of progress will often require several months and progress towards the goals established should be monitored on a regular basis. This will help maintain motivation for the programme as well as identify the areas where the programme may have to be re-evaluated. A suggested schedule for monitoring the udder health of a herd is presented in Table 17.4.
A mastitis control programme, even when successful, requires follow-up। Bulk milk somatic cell count or indirect somatic cell estimates is a basic means for permanent monitoring of udder health. Inflammation and infection percentages on a cow and quarter basis are useful tools in addition to other health and management reports. Ultimately, success of a mastitis control programme depends on active participation of all parties involved. The dairy farmers or farm personnel must appreciate the importance of all elements of the control programme. Emphasis should be made on positive reinforcement of goals and profit to be received. Inclusion of all the parties involved in the mastitis control team and recognition for an effort that results in success should be part of the plan. The link to record keeping as part of herd recording schemes should also be recognised.
References and suggested readingChew B.P. 1987. Vitamin A and _-carotene on host defence. Journal of Dairy Science 70:2732.
Korhonen H. and Kaartinen L. 1995. Changes in the composition of milk induced by mastitis. In: Sandholm M., Hankanen-Buzalski T., Kaartinen L. and Pyorala S. (eds), The Bovine Udder and Mastitis'. Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland.
MAAC. (Ministry of Agriculture and Agricultural Cooperatives). 1997. The VIIIth National Economic and Social Development Plan (1997-2001). Dairy Development Plan, Office of Agricultural Policy and Development.
NMC. (National Mastitis Council). 1987. Laboratory and Field Handbook on Bovine Mastitis. The National Mastitis Council, Madison, USA.
NMC (National Mastitis Council). 1996. Current Concepts of Bovine Mastitis. Fourth edition. The National Mastitis Council, Madison, USA.
Nickerson S.C. 1993. Vaccination programs for preventing and controlling mastitis. In: Proceedings of the National Mastitis Council Regional Meeting, Syracuse, New York, USA. pp. 64-72.
Philpot W.N. 1997. Quality milk production and masitis control. A comprehensive manuscript to be used as a basis for seminars and workshops. Philpot and Associates International, Inc. LA, USA.
Philpot W.N. and Nickerson S.C. 1991. Mastitis: Counter Attack. A Strategy to Combat Mastitis. Babson Bros. Co., Illinois, USA.
Sandholm M., Honkanen-Buzaki T., Kaartinen L. and Pyorala S. 1995. The Bovine Udder and Mastitis. Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland.
Sukrawee U. 1997. Personal Communication. Thai Dairy Industry Co. Ltd.
Taponen J. and Myllys V. 1995. The economic impact of mastitis. In: Sandholm M., Hankanen-Buzalski T., Kaartinen L. and Pyorala S. (eds), The Bovine Udder and Mastitis. Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland.
Thirapatsakun T. 1989. Mastitis: 1) Estimate of Annual Economic Loss. Journal of Thai Veterinary Medical Association 40:59-63. (English abstract).
