Bovine Mastitis: Diagnosis and treatment Pashu Sandesh

Bovine Mastitis: Diagnosis and treatment

Pashu Sandesh, 16th July 2018

Asha Kumari Verma, Akshay Kumar, Dileep Kumar Yadav

Mastitis is a major endemic disease causing fatal inflammatory condition of mammary gland and udder tissue affecting reproductive performance in dairy cattle.Mastitis has a multifactorial etiological agent closely related to the production system and environment where cows are being reared.Mastitis occurs as an immune response to bacterial invasion into teat canal or occasionally by chemical, mechanical or thermal injury to the cow’s udder tissue.

Mastitis results in the high incidence of clinical mastitis and prevalence of subclinical mastitis thus having high economic importance due to the costs associated with treatment, production losses, and reduced animal welfare. Losses in total milk production range from 5.0 to 25.0%, with one extreme of 83.9%. In terms of milk losses per quarter per day, 0.76 to 5.86 lb, or 9.0 to 43.3%, have been observed. Decreases in the composition of milk have been recorded for fat, 0.1 to 0.45%; solids-not-fat, 0.1 to 0.57%; lactose, 0.1 to 0.77%; and total solids, 1.07%.

Total annual economic losses due to dairymen in the United States attributable to mastitis have been estimated at $400 to $500 million, or $23 per cow. Other estimates obtained during various stages of a control program indicate annual losses per cow of $23.26 to $154.34 before, and averaging $28.09 to $82.00 after, the initiation of such a program. Control of this costly disease must be based on a continuing program of prevention and elimination of infection. Instituting and maintaining such a program can reduce losses from mastitis by 50% or more.

A study conducted in Central Region of India revealed that losses in due to mastitis in monetary terms were estimated to be INR1390 per lactation, among which around 49% was owing to loss of value from milk and 37% on account of veterinary expenses. Crossbred cows affected during mastitis period were found to show higher losses due to high milk production The cost of treating an animal was estimated to be INR509 which includes cost of medicine (31.10%) and services (5.47%).

Pathogenesis:

Mastitis causing pathogen spreads from cow-to-cow (contagious pathogens) or from herd's surroundings (environmental pathogens), such as bedding materials, manure and soil. This distinction play a major role in assessing the challenges present in a herd and accordingly measures can be taken to reduce or treat mastitis.

The contagious pathogens habituating in cow’s udder and teat spread from affected cow (or quarter) to unaffected cow (or quarter) during milking. These pathogens have less survival rate in environment thus post-milking teat disinfection and dry cow therapy plays an important role in controlling contagious mastitis. Farms with a high level of contagious mastitis often have high Somatic Cell Counts (SCCs) with relatively normal Bactoscan results. The major organisms involved are Streptococcus agalactiae, Staphylococcus aureus, or Mycoplasma.Contagious pathogens spread during milking by milkers’ hands or the liners of the milking unit.Some may spread from cow to cow through aerosol transmission and invade the udder subsequent to bacteremia such as Mycoplasma spp.

Environmental mastitis pathogens which resides in the cow’s environment such as feces, soil, bedding or water and may get transferred when the cow is loafing, eating or lying down. These pathogen can enter the teat canal due to the contact of teat with these environmental factors during milking or between milking.The major organisms causing environmental mastitis include the coliforms, the environmental Streptococcal species, and Pseudomonas species. Other opportunistic agent present in environment may cause mastitis too.The efficacy of these environmental pathogens to adhere to and colonize the teat is less as compared to contagious pathogen; dry cow therapy has little value in their control as these kinds of infections do not carry from one lactation to the next. High levels of environmental pathogens in a herd may cause normal SCCs but higher than average Bactoscan results.

The bedding material act as primary source of environmental mastitis, but contaminated teat dips, intra mammary infusions, water used for udder preparation before milking, water ponds or mud holes, skin lesions, teat trauma, and flies have all been incriminated as sources of infection.Sometimes flies can transmit Actinomyces pyogenes resulting in abscesses and purulent mastitis in dry cows and heifers which is called as ‘summer mastitis’.

These pathogens can infect cows both during the dry period and lactation, and understanding pathogenesis will help to identify and recognize the source of these infections, as approaches to control, prevention and treatment of the pathogen's effects depend upon this.

Symptoms

According to their symptomatology, mastitis can be classified mainly into Per acute, Acute, Subacute, and Chronic; Clinical and Subclinical mastitis. Major symptoms include redness, swelling, pain, heat and even result in functional loss such as decrease in milk production and change in milk composition, as well as anatomical changes in udder.

Per acute mastitis :Sudden onset with severe inflammation of the udder, serous milk which may lead to agalactia. Systemic involvement due to septicemia or toxemia can be observed. Others symptoms include fever, anorexia, depression, decreased rumen motility, dehydration, and sometimes death of the cow.

Acute Mastitis: Sudden onset with moderate to severe inflammation of udder causing decreased production, and serous milk or fibrin clots in milk. It shows similar signs as per acute mastitis but is less severe.

Subacute Mastitis: There is mild inflammation of udder with no visible changes in udder, with presence of small flakes or clots in the milk, and the milk may have an off-color. Generally no systemic illness is found.

Chronic Mastitis: Generally persists as subclinical mastitis for months or years and may show occasional flare up to clinical form

Subclinical Mastitis : It is the most common form of mastitis. No visible changes are observed in the udder and milk . There is decreased production and decreased milk quality.

Detection of mastitis

Ideal means to prevent and control mastitis is detection of mastitis. Following approach can be followed for detection of mastitis:

Visualization and palpation of the udder: Udder exhibit the sign of inflammation during mastitis characterized by hardness, redness, and hotness and pain upon touching. During inflammation, changes in vascularity and blood flow to the gland may result in these symptoms.

Visualization of the milk : Visible changes due to the presence of flakes, clots or seruous milk is the most common means of detection of clinical mastitis. Strip first few squirts of milk from each quarter into a strip cup at the beginning of milking for detecting flakes or clots in the milk.

Detection of Somatic Cells: As a key response to the inflammation there is migration of leukocytes to the udder that enter the milk in the alveoli are called somatic cells and there concentration in milk is called somatic cell count (SCC). The higher level of inflammation in the tissue characterized by high SCC. SCC in milk provide useful information of the inflammation status of the udder. Several methods are being used for detecting somatic cells in milk, including the California Mastitis Test (CMT; a cow-side test),the Wisconsin Mastitis Test (WMT; on-farm test), Microscopic Somatic Cell Count (usually requires a laboratory), Electronic Somatic Cell Counting (requires sophisticated equipment).

California Mastitis Test (CMT)

It is a simple, inexpensive, rapid screening test for mastitis which offer a very rough estimate of the SCC for each quarter. This allows focusing on treatment efforts on that particular quarter. The test is based upon the amount of cellular nuclear protein present in the milk sample. It detects formation of gel when DNA in somatic cells reacts with detergentThe CMT reflects the SCC level quite accurately and is a reliable indicator of the severity of infection.

The CMT can evaluate composite milk samples as well as bulk tank milk. The appropriateness or value of CMT evaluation of bulk milk decreases as herd size increases.

CMT score N equates with SCC level of 200,000 cell/ml or less which is considered to be the physiological level for milk from uninfected cows. CMT Score T (trace) corresponds to a SCC level of 200,000 to 300,000 cells; the level at which infection is more likely and at which mastitis pathogens are likely to be isolated.

CMT can also be used for screening of suspected new mastitis infections, and animal's quarters to be sampled for SCC determination of bacterial culture. This will be helpful for selecting cows for further evaluation (milk culture), culling, selective dry cow treatment or extended therapy.

It is generally not recommended that CMT results alone be used for immediate treatment unless the specific pathogen is known or is performed in accordance with a treatment protocol recommended by a veterinarian. Recording inpidual cow scores on a monthly basis is a very effective system used for monitoring mastitis particularly in smaller herds.

Electrical Conductivity

Electrical conductivity of mastitis milk is higher than normal milk. The tissue damage results in subsequent increase in sodium and chloride ions in milk. Conductivity sensors are being incorporated in many new automated milking systems. Electrical conductivity can be used routinely for early detection as these changes are associated with earliest manifestations of new infections. Sensitivity and specificity of electrical conductivity between herds varies which is limitation for this test

Hand held conductivity meters or in-milk line instrumentation can be useful for routine screening of animals pre milking. The latter is the basis for the computerized milking systems that track electrical conductivity measurements on milk of cows at each milking. This data can be analyzed by computer programs to flag cows that have milk electrical conductivity that is altered from normal.

Laboratory Tests

Bulk tank Somatic cell counts (BTSCC)

Bulk tank somatic cell counts (BTSCC) are reported to dairy producers on a routine basis (usually bimonthly) by milk buyers as a measure of milk quality. BTSCC scores can also be used to monitor the level of udder health.

In general BTSCC less than 200,000 cells/ml indicate a minimal level of infection, however a series of BTSCC’s over 500,000 cells/ml indicate a problem with subclinical or chronic infection. Because the BTSCC is a function of both the quarter infection rate and the severity of infections, attempts to predict the infection status from a single BTSCC are usually unsuccessful.

Inpidual Cow Somatic Cell Counts (SCC)

The most important factor affecting the SCC of milk from a quarter, cow or herd is the infection status of the quarter. Various authors have reported average SCC for uninfected quarters to be 170,000 to 214,000 cells/ml or a geometric mean of 106,000 cells/ml. Somatic cell response of infected cows will depend somewhat on the pathogen present. Minor pathogens such as C. bovis and coagulase-negative Staphylococcus average 227,000 cells/ml when all age groups are considered. Animals infected with major pathogens (Streptococcus agalactiae, Staphylococcus aureus, Environmental Streptococci) produce average counts greater than 600,000 cells/ml.

Inpidual cow somatic cell counts are the product of the SCC measurement of all milk from all four quarters and the level of production of the inpidual quarters. The number of infected quarters as well as the total milk production become important factors in being able to accurately classify a cow as infected by means of SCC. The dilution effect of normal milk can mask infection.

Linear Score

Official test scores of somatic cell counts are typically reported as Log linear scores of the raw SCC. Log linear scores provide a more accurate and direct measure of milk losses associated with increasing SCC as demonstrated in the table below. An increase in 1 Linear Score unit equals a loss of 1.5 pounds of milk per cow per day or 400 pounds per lactation (the loss for first lactation animals is half that amount). The raw SCC can be deceiving when trying to relate milk loss relative to SCC since the milk loss is much greater at lower counts than higher counts.

Monthly variations in Linear Score (LS) of inpidual cows is small making LS measure of SCC more repeatable than the raw score. The average LS give a less distorted and more accurate picture of a lactation than does the average raw SCC. For these reasons LS is used most frequently when analyzing and graphing SCC data.

Milk Cultures

Culturing milk from the bulk tank, inpidual quarter or cow, groups or categories of cows adds an additional dimension to evaluating udder health and mastitis control programs especially when that information is combined with SCC or clinical mastitis data. This information not only provides a snap-shot in time of the udder health situation of a herd it provides a very effective means of plotting of identifying infection trends, identifying herd risk factors and monitoring herd performance and management interventions. Routine milk cultures should be an ongoing part of any mastitis control program. The sampling strategies for any ongoing program require the input of the herd veterinarian as well as herd management.

Bulk Milk Cultures

Sampling the bulk tank milk (BTC) is a simple, inexpensive means of determining the presence of mastitis pathogens in a herd. This culturing method does have its limitations and is best suited for the identification of contagious mastitis pathogens and for monitoring the presence of pathogens over time. In no way does the presence of a pathogen or the relative numbers of a specific pathogen present on the plate indicate the prevalence of infection within the herd. Bulk tank culture results not only reflect the mastitis pathogens present in a herd but also identify those organisms may contaminate milk from the teats of cows milking environment or milking equipment

Test sensitivity varies by pathogen. QMPS data indicate test sensitivities for a single bulk tank sample of 90%, 75% and 50% respectively for Streptococcus agalactiae, Staphylococcus aureus and Mycoplasma spp. respectively. Herd or group size may also be an issue due to the dilution factor of large cow numbers. BTC from herds with a low prevalence of infection with a specific organism, especially contagious pathogens (Staphylococcus aureus, Streptococcus agalactiae, and Mycoplasma spp.) may not always indicate the presence of those pathogens. Therefore BTC results should always be considered when collected as a series of tests over a given period of time. This is absolutely necessary when monitoring the progress of existing pathogen elimination programs or when screening herds or groups of animals as part of a pre purchase screening program. The sampling interval should be based on herd dynamics. Generally BTC for monitoring open herds should be bimonthly or monthly. When screening animals for purchase three bulk tank samples over a one-week period is most often recommended. Figure 1. clearly demonstrates the influence of sampling frequency and test specificity on the probability of detection of a specific pathogen in a bulk tank milk sample.

Inpidual Cow Samples

Inpidual animal cultures provide another method of diagnosing mastitis. Cultures alone provide an indication of the possible pathogen involved. However the possibility of a false positive result due to contamination of the sample with organisms present in the teat canal, teat skin or environmental contamination of the sample will affect test specificity. Infected animal not currently shedding pathogens may have a negative culture result hereby affecting test sensitivity. Test sensitivity and specificity are about 70% for single cultures. When multiple samples of the same animal are take sensitivity remains about the same however test specificity increases to 80 – 90 %. These results are species specific.

Inpidual cow culture results become much more meaningful when combined with SCC results. Using SCC to select cows to be sampled for milk culture (animals at higher risk for infection) ensures a relatively good predictive value for the culture results. Using two tests simultaneously to evaluate animals will increase the sensitivity but decrease the specificity (slightly) the combined tests.

Mastitis Treatment

Antibiotic treatment: Typically when clinical mastitis is detected, the cow is milked out and then given an intra mammary infusion of antibiotic, ie. infused directly into the infected gland. Clinical mastitis symptoms are indicated in the Mastitis Clinical Syndromes resource, but most often are recognized by the milker from detection of clots or flakes in the milk, from a cow that has a quarter sensitive to the touch (she kicks a lot when you touch a particular quarter), a quarter that is swollen or hot to the touch. Because the cow's udder then contains antibiotics which must be kept out of the food supply, that cow's milk must not be put into the milk tank for some specified number of milkings after treatment. Typically this milk is either dumped down the drain or used to feed calves. Clear identification of the treated cow is critical to be sure the cow's milk is not inadvertently put into the milk tank. Shipping milk contaminated with antibiotics can lead the producer to lose their permit to ship Grade A milk; that is they are out of business. use of leg-bands or some other physical marker on the cow, as well as clear records of antibiotic administration are essential for this process. It is quite common for a cow to be treated multiple milkings with the antibiotics.

Intra mammary infusions: Prior to intra mammary infusion, the teat is cleaned well and the tip of the teat is swabbed with an alcohol swab and allowed to dry for a number of seconds. The antibiotic comes in a plastic tube with a plastic infusion cannula on the end. Historically these have been long cannulas and the cannula was inserted completely through the streak canal (called full insertion). However, it was realized that this could be carrying bacteria into the teat cistern. More recently a shorter infusion cannula has been used in what is called a partial insertion method where the cannula only goes about half-way up into the streak canal and the antibiotic is expelled from the tube into the teat cistern. After emptying the antibiotic tube, the teat is pinched off and the antibiotic fluid is palpated up into the gland.

Oxytocin treatment: A key contributing factor to duration of mastitis is the frequency and completeness of milk removal from the infected quarter. In some cases, cows are stripped between normal milking times, sometimes with injection of oxytocin to stimulate an effective milk let down. Clearly removal of the primary growth medium of the bacteria, the milk, more often should enhance rate of recovery from infection.

Non-responding cases: Inspite of the natural resistance mechanisms of the cow, antibiotic treatment to help her fight bacterial infection, and other methods such as frequently stripping out the milk, some cows are unable to eliminate the infection. These are often considered to be chronically infected cows, typically with Staph. aureus, and remain a constant source of infection for other cows. Culling of chronically infected cows sometimes is the only way to effectively control spread of mastitis in the herd.

Control of Mastitis

Awareness of the economic losses associated with mastitis is resulting in a desire for mastitis control programs. Control programs are focused on detection of mastitis (by the above methods), identification of the causative agent(s) and prevention of transmission by removing the source of the agent (milk contaminated fomites, bedding, persistently infected cows, etc.). Knowledge of mammary anatomy and physiology, mammary defense mechanism, microbial habitats, microbial virulence factors, milking machine function, and antibiotics/germicides is important in achieving effective mastitis control.

Control of Contagious Mastitis :

Contagious mastitis can be effectively controlled through a rigorous program of teat dipping and dry cow antibiotic treatment. Teats must be dipped in germicide after each milking (this decreases incidence of the disease). Each quarter must be treated with dry cow antibiotics at end of lactation (this decreases prevalence of the disease). Cows with contagious mastitis should be milked last or a separate milking claw used for the infected cows. Milking claws should be flushed with hot water or germicide after milking infected cows (called back flushing). Inpidual cloth/paper towels should be used to wash/dry teats. Milkers should have clean hands and wear latex gloves. New additions to the herd should be cultured and persistently infected cows should be culled. Teat lesions should be minimized (from chapping, frostbite, stepped-on teats, lacerations, or machine damage). Heifers can be given dry cow antibiotic treatment during gestation if S. aureus is a problem in the heifers.

Control of Environmental Mastitis : Environmental pathogens are more difficult to control than the contagious pathogens. Many of these organisms are resistant to germicides in teat dip and antibiotics in dry cow therapy. Identification of the source and removal (bedding, ponds, mud) is the key to control. Udders can be clipped to minimize the amount of manure clinging to the glands. Only clean dry teats should be milked. Teats should be pre-dipped with germicide before milking. Cows should be kept standing after milking (offer them feed). Sterile single-dose infusion products should be used and sterile infusion techniques (alcohol swab) should be used. The milking parlor should be kept clean. The teat dipper should be kept clean; organisms an survive in many germicides. Pipelines/water heater may need to be replaced in cases of Pseudomonas contamination.

Control of Mastitis

Control of Contagious Mastitis : Contagious mastitis can be effectively controlled through a rigorous program of teat dipping and dry cow antibiotic treatment. Teats must be dipped in germicide after each milking (this decreases incidence of the disease). Each quarter must be treated with dry cow antibiotics at end of lactation (this decreases prevalence of the disease). Cows with contagious mastitis should be milked last or a separate milking claw used for the infected cows. Milking claws should be flushed with hot water or germicide after milking infected cows (called back flushing). Inpidual cloth/paper towels should be used to wash/dry teats. Milkers should have clean hands and wear latex gloves. New additions to the herd should be cultured and persistently infected cows should be culled. Teat lesions should be minimized (from chapping, frostbite, stepped-on teats, lacerations, or machine damage). Heifers can be given dry cow antibiotic treatment during gestation if S. aureus is a problem in the heifers.

Vaccination for Mastitis

Development of potential vaccines to prevent or control mastitis continues to be an important goal. Excellent progress has been made toward coliform mastitis control with the development of mutant gram negative vaccines. The organisms used (E. coli and Salmonella) have lost the ability to synthesize outer polysaccharide antigens, resulting in exposure of common gram negative LPS (lipo-polysaccharide) antigens. Antibodies produced against these antigens are cross-reactive among gram negative pathogens. When used as directed, there is approximately a 70% decrease in clinical coliform mastitis, as well as a decrease in severity of clinical signs.

Escherichia coli J-5 vaccine provides a safe and effective way to control E.coli mastitis. Three dose of vaccine with a 5 ml dose at 7 and8 months of gestation followed by third dose within two weeks postpartum is given to cows or heifers which shortens duration of E.coli mastitis by 41%.

Cost: benefit ratio is high in problem herds. Many attempts have been directed toward development of an effective vaccine for Staphylococcus aureus. Vaccines have been created (e.g. from Protein A) and injected intramuscularly or into the area of the supra mammary lymph node. Vaccination has been unsuccessful in reducing the number of new cases of mastitis. Some vaccines have been effective in improving spontaneous cure rates and reducing severity of infection. These vaccines result in an increase in all types of leukocytes in the gland, thus improving defense. Overall, the success of vaccination has been minimal. Most of these vaccines have used bacteria cultured in-vitro, have been killed vaccines, and have stimulated production of IgG1. Development of a Staph aureus vaccine is an ongoing objective of much research.

Asha Kumari Verma¹, Akshay Kumar²,Dileep Kumar Yadav³

1. Department of Veterinary Public Health, IVRI, Izzatnagar, Bareilly U.P.2,3. Department of Gynecology and Obstetrics, College of Veterinary Sciences and Animal Husbandry, U.P. Pandit Deendayal Upadhayaya Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go AnusandhanSansthan, Mathura - 281001, Uttar Pradesh, India

Corresponding author: Asha Kumari Verma ashav223@gmail.com