A Look into Bovine Mastitis: Its Pathophysiology and Management

Jayashree Gogoi*¹

^*1, Animal Physiology & Reproduction Laboratory, ICAR-National Dairy Research Institute, Eastern Regional Station, A-12, Kalyani

^*Corresponding author email: Jayashreegogoi678@gmail.com

Abstract

Udder Health is one of the most important aspects of dairy cow health. Mastitis causes huge economic losses to farmers every year worldwide and has a negative influence on milk’s technological value.  A detailed understanding of the pathophysiology of mastitis will help in planning better preventive measures and in formulating new research treatments of mastitic animals. The aim of the article is to understand the pathophysiology of bovine mastitis and focuses on the management, handling, and prevention of bovine mastitis.

Introduction

“Mastitis” describes an inflammatory reaction in the mammary gland. The term mastitis is derived from the Greek word masto referring to the mammary gland and it is meaning “inflammation” (Blood and Studdert, 1999). Although “mastitis” can technically be used to describe any udder injury which may result in inflammation, it is generally accepted that the causative agents for the inflammatory reaction are microorganisms that have gained entry into the teat canal and mammary tissue. The extent of the infection that occurs as microorganisms multiply and proliferate within the mammary tissue determines the type of mastitis affecting the cow udder. Bovine mastitis is a disease complex that occurs in acute, gangrenous, chronic, and subclinical forms of inflammation of the bovine udder, and is due to a variety of infectious agents, such as microorganisms. Animal care, hygiene, and management are important factors in this dairy cow disease of great economic importance. Field surveys of major livestock diseases have ranked mastitis as number one disease of dairy animals (Khan and Khan, 2006). Mastitis still continues to be one of the most costly diseases of dairy animals. Milk from cows who are suffering from mastitis has an increased somatic cell count. Prevention and Control of mastitis requires consistent care in sanitizing the cow barn facilities, proper milking procedure and segregation of infected animals and extensive use of antibiotics to treat and prevent this disease.

Pathophysiology of mastitis

Invasion of the teat most often occurs during milking. The teat is the first line of defense against invading microorganisms such as bacteria into the udder. Infections start when microorganisms start penetrating the teat canal and multiplying in the mammary gland. The sphincter muscle closes the teat canal tightly when the cow is not being milked. Upon entry of the microorganisms in the milk or at the teat end, organisms are pushed towards and into the teat canal and cistern. Teat canal remains dilated for one to two hours after milking even then the canal of a damaged teat may remain partially open permanently. Organisms from the environment (manure, bedding, etc.) or those found on injured skin at the tip of the teat may easily invade an open or partially open canal. Some bacteria may enter into the udder by attaching and colonizing new tissue while others may move around via milk current produced by the cow’s movement. At first the Bacteria will damage the tissues lining the large milk-collecting ducts. During the process of damage of tissues, bacteria encounter white blood cells such as leukocytes which are present naturally in small numbers in the milk. Leukocytes are the cow’s second line of defense because they can engulf and destroy bacteria (Harmon et al., 1994) Leukocytes help release substances which causes the movement of additional leukocytes from the blood into the milk. If bacteria are not entirely destroyed, they continue to multiply and begin to invade smaller ducts and alveolar areas. Milk secreting cells damaged by toxins and other irritants release substances that lead to increased permeability of blood vessels. Additional leukocytes along with fluids, minerals and clotting factors move to the site of infection by squeezing between the damaged milk secreting cells.  Clotted milk may help isolate the infected regions by closing the ducts. Sometimes the infection is cleared by opening of the clogged ducts which rapidly eliminates the microorganisms which causes the milk composition and production return to normal. However, if the infection persists, the ducts remain clogged, the entrapped milk causes the secretory cells to revert to a resting (non-producing) state and the alveoli begin to shrink. Substances released by leukocytes lead to the complete destruction of alveolar structures, which are replaced by connective and scar tissues. The damaged milk secretory is in effect the cow’s third line of defense to bring the infection under control. Biofilms are a group of cells confined in self-produced matrix, which are tolerant to opsonophagocytosis and conventional antiobiotics as a result of which leads to antimicrobial resistance (Stewart and Costerton, 2001).. Recurrent infections are often attributable to biofilms (Vasudevan et al., 2003). Biofilm formation can lead to damage to host tissues since it can promote the phagocyte release of lysosomal enzymes, reactive oxygen and nitrogen species (McAuliffe et al., 2006; Hermeyer et al., 2011). Thus as the disease progresses the number of somatic cells in the milk becomes elevated and associated with a (permanent) reduction in milk yield. Compositional changes accompany the elevation of SCC and inflammation in an infected mammary gland (Kitchen et al., 1981, Matila, 1985). Mastitis or elevated SCC are associated with a decrease in lactose, a-lactalbumin, and fat in milk because of reduced synthetic activity of the mammary tissue. Some components, such as lactose (Shuster et al., 1981) and a-lactalbumin (Mcfaden et al., 1988), may leak out of the alveolus between epithelial cells; these components have been measured in urine or blood of cows with mastitis. The pH may increase from a normal of 6.6 to 6.9 or higher because of the movement of blood components into milk (Kitchen et al., 1981). Many enzymes and other whey proteins originating from damaged tissue, the blood, or leukocytes are elevated in milk. Examples of enzymes that may have increased activity are acid phosphatase, antitrypsin (antitrypsin or al protease inhibitor), alkaline phosphatase, arylsulfatase, 8- glucuronidase, catalase, glutamic-oxaloacetic transaminase, lactate dehydrogenase, lipase, lysozyme, Nagase, plasmin, xanthine oxidase, and various esterases (Kitchen et al., 1981). Plasmin, an important proteolytic enzyme in milk with high SCC is normally found in milk; however, there may be more than 2-fold increases in its activity in milk during mastitis. Figure 1 describes the pathophysiology of mastitis in a flowchart manner

Mastitis causing Bacteria

Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus agalactiae, Streptococcus uberis, Brucella melitensis, Corynebacterium bovis, Mycoplasma spp. (including Mycoplasma bovis), Escherichia coli (E. coli), Klebsiella pneumonia, Klebsiella oxytoca, Enterobacter aerogenes], Pasteurella spp, Trueperella pyogenes(previously Arcanobacterium pyogenes), Proteus spp, Prototheca zopfii (achlorophyllic algae), Prototheca wickerhamii (achlorophyllic algae)

Staphylococcus aureus is the species most frequently isolated from bovine mastitis, a disease responsible for significant economic losses all over the world (Costa et al., 1998). The organisms that fit into this category include: Staphylococcus aureus (coagulase positive staphylococci), Streptococcus agalactiae and the less common sources of infection caused by Corynebacterium bovis and Mycoplasma bovis (Quinn, et al., 1999). Coliform bacteria are normal inhabitants of soil and the intestines of cows. They accumulate and multiply in manure and bedding. Coliforms can cause mastitis only if contaminated particles from the environment come in contact with the udder the coliform do not attach to the ducts and alveoli in the udder, rather they multiply rapidly in the milk and produce toxins that are absorbed into the blood stream. Cows free of other mastitis-causing bacteria (streptococcus agalactiae and staphylococcus aureus appear to be more susceptible to coliform bacteria.

Many other bacteria and even yeasts may be responsible for causing mastitis, but are less common and occur if conditions change to increase exposure to these organisms. A condition known as “summer mastitis” occurs mostly in European countries in the summer months when wet, rainy conditions prevail. The source of infection is usually traced to an increase in exposure of the cows to flies in pastures that transmit infecting Arcanobacterium pyogenes and Peptostreptococcus indolicus strains and is more common in non-lactating cows (Sol, 1984)

Types of Mastitis

There are several ways of classifying mastitis. Mastitis can divided as two major groups depending upon the type of infectious agent and route of transmission

1. Contagious Mastitis: Contagious mastitis is caused by contagious microorganisms are Staphyloccous aureus and Streptococcus species bacteria which live on the skin of the teat and inside the udder. Contagious mastitis can be transmitted from one cow to another during milking (Bogni et al., 2011)
2. Environmental mastitis: Environmental mastitis is caused by pathogens normally found in feces, contaminated bedding materials, and feed. Streptococcus species and Gram- negative bacteria (Escherichia coli and Klebsiella) are examples of microorganisms included in this group (Bogni et al., Cases of environmental mastitis rarely exceed 10% of the total mastitis cases in the herd.

Contagious mastitis can be divided into three groups.

1. Clinical mastitis

2 Sub clinical mastitis

3.Chronic mastitis

1.       Clinical mastitis

Clinical mastitis is characterized by the presence of gross inflammation signs like swelling, heat, redness, pains. Clinical mastitis is caused mostly by organisms such as Streptococcus uberis and streptococcus dysgalactiae. Streptococcus uberis are found in bedding (especially organic bedding: straw, sawdust, etc.), standing water and soils. They can also be found on the cow’s skin (teat and belly) and in the reproductive organs. These two organisms are usually transferred from the environment to the teat between milking, but some transfer can also take place during milking. These organisms cannot be eliminated from a herd because they are part of the normal environment

Three types of clinical mastitis exist

a.      Peracute mastitis

Peracute mastitis is characterized by gross inflammation, disrupted functions such as reduction in milk yield, changes in milk composition and systemic signs (fever, depression, shivering, loss of appetite and loss of weight

b.      Acute mastitis

Acute masititis is similar to peracute mastitis, but with lesser systemic signs such as fever and mild depression.

1. Sub-acute mastitis

In this type of mastitis, the mammary gland inflammation signs are minimal and no visible systemic signs.

2 Sub-clinical mastitis

This form of mastitis is characterized by change in milk composition with no signs of gross inflammation or milk abnormalities. Changes in milk composition can be detected by special diagnostic tests. Streptococcus agalactiae is the most common cause of subclinical infections but rarely causes severe illness (acute mastitis). This organism lives in the cow’s udder and survives only a short time outside the mammary gland. This organism may also infect the udder of a young calf if it is sucked by a second calf that has been fed contaminated milk. The infection can remain indefinitely in the heifer’s mammary gland. Streptococcus agalactiae can be eradicated from a herd by appropriate treatment combined with good milking practices. However, it may easily spread again in a herd after the purchase of an infected animal.

3.Chronic mastitis

Chronic mastitis is characterized as inflammatory process that exists for months, and may continue from one lactation to another. Chronic mastitis for the most part exist as sub-clinical but occasionally exibit  periodical flare- ups, sub-acute or acute form, which last for a short period of time.

Mode of transmission

1. Mastitis is most often transmitted by repetitive contact with the milking machine, and through contaminated hands or materials (figure 2a, 2b).
2. Another route is via the oral-to-udder transmission among calves (figure 2d). Feeding calves on milk may introduce some mastitis causing bacteria strain in the oral cavity of the calf where it will stay dormant until it is transmitted elsewhere. Since grouped calves like to stimulate suckling, they will transmit the bacteria to the udder tissue of their fellow The bacteria will lay dormant in the udder tissue as the calf grows until it begins to lactate. That is when the bacteria activates and causes mastitis.
3. Management practices such as pathogens from manure (figure 2e), contaminated bedding( figure 2c) , soil water may gain entry into the cows udder and lead to bovine.

Management of Mastitis

Effective screening and diagnosis is the proper way of managing mastitis cases. The usual method of screening mastitis cases in cattle is by examining the udder to check for inflammation and swelling or by observing the consistency of the milk, colour of the milk.. The strip cup or strip plate is a simple, rapid and important tool in the milking parlor for determining the presence of clinical mastitis. The test is performed by squirting a few streams of the foremilk onto the strip cup and then it is visually examined for milk abnormalities.  Another method of detection is the California mastitis test, which is designed to measure the milk’s somatic cell count as a means for detecting inflammation and infection of the udder. The Rapid Mastitis Test (or Californian Mastitis Test) is a cow-side test that detects subclinical mastitis in individual quarters by the presence of cells in milk samples. The test uses a small amount of milk from each quarter which is squirted into a dish at milking and an equal amount of detergent reagent is added. The solution is swirled to mix it, and the amount of gel reaction is assessed. Gel reaction scores are given such as negative if the scc is less than 2,00,000 trace if the scc is between 150,000 – 500,000, and if its more than 400,000 then 1+, 2+, 3+ scoring is given according to visible changes in the milk . Electronic Somatic Cell Count is an automated and centralized system for somatic cell count which is used by Dairy Herd Improvement Associations. The procedure is more precise than the CMT and the WMT.

Other tests include the electrical conductivity (EC) test which measures the increase in conductance in milk caused by the elevation in levels of ions such as sodium, potassium, calcium, magnesium and chloride during inflammation. Advantage: can be used ‘on-site’. Disadvantage: non-mastitis- related variations in epithelial cell can present problems in diagnosis. Then the rise in milk pH, due to mastitis, is detected using bromothymol blue. Advantages is it is user friendly, cost effective and rapid. Disadvantage is it is not as sensitive as other tests.Enzymes Assays are used to detect enzymes, such as NAGase and LDH. Advantage: assays are rapid. Disadvantage: assays might be laboratory-based. Wisconsin mastitis test is a on farm mastitis test used to test detect mastits in bulk samples based on increase in leucocytes is accompanied by an increase in viscosity when a detergent reagent is mixed with a milk sample.

Control of Mastitis

Control of mastitis requires a combination of preventive and therapeutic measures Prevention is the key in mastitis control and which will markedly reduce the incidence of mastitis. The prevention of mastitis can be achieved by:

1. Proper milking hygiene should be followed as bacteria can be transmitted from the contaminated hands of the milker. Thus the milker’s hands should be washed thoroughly with disinfectant and soaps before milking and clinically infected cows should be milked last. Teats should be cleaned and dried before milking.
2. Milking machine should be kept in good operating condition. Vacuum level in the milking unit should be between 275 and 300 mm of mercury with little fluctuation. The vacuum regulator should be kept clean and checked
3. Dipping the teats with suitable disinfectant after milking reduce existing infection up to 50% when suitable disinfectant is used to immerse or spray the teats
4. Dry cow therapy is the best way to cure chronic and subclinical mastitis that are difficult to treat successfully during
5. Culling of chronically infected cows is an effective method
6. Proper nutrition should be given to animals to avoid deficiencies. Deficiencies of selenium and vitamin E in the diet have been associated with an increased rate of new mammary
7. Treatment with antibiotics may be systemic (injected into the body), or they may be forced upwards into the teat through the teat canal (intramammary infusion). but milk from the treated cows is not marketable until drug residues have left the cow’s system. Special test are there to determine the levels of antibiotic residues in milk
8. Vaccinations for mastitis are available such as best Vac, Startvac, Hipra, Spain but as they only reduce the severity of the condition, and cannot prevent reoccurring infections, they should be used in conjunction with a mastitis prevention program

Conclusion

          Mastitis is one of the most common multifactorial diseases. Mastitis can be prevented by proper management and new effective, innovative solutions to treat mastitis. However, the focus should be in enhancing its preventive measures to avoid huge economic loss especially among dairy farmers. Researchers and scientist must keep on looking new measures and methods to reduce the prevalence of mastitis.

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