Bovine Mastitis: A Threat to Economy

Research Article

Open Access

Awale MM, Dudhatra GB^*, Avinash Kumar, Chauhan BN, Kamani DR, Modi CM, Patel HB and Mody SK

Department of Pharmacology and Toxicology, College of Veterinary Science and Animal Husbandry, Sardarkrushinagar Dantiwada Agricultural University, Sardarkrushinagar-385506, Gujarat, India

^*Corresponding authors:

Dudhatra GB
Department of Pharmacology and Toxicology
College of Veterinary Science and Animal Husbandry
Sardarkrushinagar Dantiwada Agricultural University
Sardarkrushinagar-385506, Gujarat, India
E-mail: fmuckun@chla.usc.edu

Received August 30, 2012; Published September 03, 2012

Citation:Awale MM, Dudhatra GB, Avinash Kumar, Chauhan BN, Kamani DR (2012) Bovine Mastitis: A Threat to Economy. 1:295. doi:10.4172/scientificreports.295

Copyright:© 2012 Awale MM, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract

Bovine mastitis is the most complex disease condition mainly because of multiple causative agents, poor understanding of the early immune response and complexities associated with mammary epithelial cell damage by both the agents and the host factors. Decreased milk production accounts for approximately 70% of the total cost of mastitis. Though, India is the largest milk producer but per capita production is less than half of the world average. Additionally, the poor understanding of the underlying phenomenon in subclinical state of the infection complicates the therapeutic interventions. It is one of the important production diseases of dairy animals which directly or indirectly affect the economy of the farmers and ultimately affect the economy of the country. However, mastitis is a global problem as it adversely affects animal health, quality of milk and economics of milk production and every country including developed ones suffer huge financial losses. The pattern of mastitis occurrence is also significantly increasing in both cattle and buffaloes which is a major challenge for field veterinarians and researchers.

Keywords

Bovine; Economy; Mastitis; Milk production

Introduction

Bovine mastitis is defined as inflammation of the mammary gland and, it is the most serious and economically important disease in dairy milk production worldwide [1-4]. Mastitis-related losses are associated with reduction in yield, increased treatment costs, discarded milk, increase in culling and associated dairy cow replacement rates, and financial penalties for exceeding legal milk quality limits [5,6]. If the disease is diagnosed in early stages, the greater portion of this loss can be avoided. Developing countries like India is facing major problem due to mastitis. The focus of this article is the description of pathogens, incidence, clinical characteristics, diagnosis, prevention, control, treatment and economics associated with bovine mastitis.

Etiology of Bovine Mastitis

Etiological agents of mastitis can be infectious or noninfectious. Organisms as diverse as bacteria, viruses, mycoplasma, yeasts and algae have been implicated as causes of the mastitis [7-11]. The majority of mastitis is of bacterial origin and just a few of species of bacteria account for most cases, such as Escherichia coli, Staphylococcus aureus, Streptococcus uberis, Streptococcus dysgalactiae and Streptococcus agalactiae, Streptococcus bovis, Klebsiella pneumoniae [12-20]. Other less frequent organism includes Klebsiella oxytoca, Pasteurella spp., Proteus spp., Pseudomonas aeruginosa, Nocardia, Mycoplasma spp., Brucella abortus, Corynebacterium bovis, Trueperella pyogenes, Prototheca zopfii, Prototheca wickerhamii and yeast. The Enterobacteriacae were the commonest cause responsible for 40.9% of all mastitis, and S. aureus, Str. dysgalactiae, Str. agalactiae accounted for only 10% of clinical cases [16]. Staphylococci are the bacteria most commonly isolated from subclinical mastitis [21-23]. In mastitis diagnostics, staphylococci are divided into coagulase-positive staphylococci (S. aureus) and coagulasenegative staphylococci (CNS) based on the ability to coagulate rabbit plasma. Some other Staphylococcus species, including Staphylococcus hyicus, may also be coagulase-positive [24].

Types of Mastitis

Classically, mastitis pathogens have been classified as contagious pathogens and environmental pathogens [25]. The contagious pathogens are adopted to survive within the host particularly within the mammary gland. They are capable of causing subclinical infections,which are typically manifest as an elevation in the somatic cell count (leukocytes, predominantly neutrophils and epithelial cells) of milk from the affected quarter; they are typically spread from cow to cow at or around the time of milking [26]. In contrast, the environmental pathogens are best described as opportunistic invaders of the mammary gland, not adapted to survival within the host; typically they invade, multiply, engender a host immune response and are rapidly eliminated. The major contagious pathogens comprise S. aureus, Str. dysgalactiae and Str. agalactiae; the major environmental pathogens comprise the Enterobacteriacae (particularly E. coli) and Str. uberis [16].

There are two types of mastitis:

Contagious Mastitis: It is caused by bacteria live on the skin of the teat and inside the udder. Contagious mastitis can be transmitted from one cow to another during milking.

Contagious mastitis can be divided into three types:

Clinical mastitis: It is characterized by the presence of gross inflammation signs (swelling, heat, redness, pain).

Clinical mastitis can be divided into three types:

i. Peracute mastitis: It is characterized by gross inflammation, reduction in milk yield and changes in milk composition. Systemic signs like fever, depression, shivering and loss of appetite and loss of weight.

ii. Acute mastitis: Similar to percute mastitis, but with lesser systemic signs like fever and mild depression.

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

Subclinical 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 occur.

Chronic mastitis: An inflammatory process that exists for months, and may continue from one lactation to another. It exists as subclinical but may exhibit periodical flare-ups subacute or acute form, which last for a short period of time.

Environmental mastitis

It is caused by organisms such as Escherichia coli which do not normally live on the skin or in the udder but which enter the teat canal when the cow comes in contact with a contaminated environment. The pathogens normally found in feces bedding materials, and feed. Cases of environmental mastitis rarely exceed 10% of the total mastitis cases in the herd.

Prevalence of Bovine Mastitis

Clinical mastitis is less likely in younger animals. Reduction in clinical mastitis has been a major success over the past 35 years, in countries with a developed dairy industry. Most mastitis occurs as a low grade infection, a subclinical state, which affects 10-15% cows, increasing milk leucocytes content, reducing milk production and increasing milk bacterial content. These all contribute to reduced milk value as a food and in monetary terms [27]. The prevalence of such infections is a significant risk to uninfected animals in the herd as many mechanisms exist to expose the animals to new infection. Most commonly these include the common lying areas in housing or at pasture, the milking machine and successive contact of different cows or teats by the milker preparing the teats for milking [28]. The prevalence of coagulase-negative staphylococci (CNS) mastitis is higher in primiparous cows than in older cows [29,30]. Contagious mastitis is primarily transmitted at milking time and the milking process affects the patency of the teat orifice which can increase the risk of development of environmental mastitis. Mammary quarter infection prevalence ranges between 28.9-74.6% prepartum and 12.3-45.5% at parturition. Coagulase-negative staphylococci (CNS) are the most prevalent cause of subclinical intramammary infections in heifers. Coagulase-positive staphylococci (CPS) in some studies are the second most prevalent pathogens, while in other studies the environmental mastitis pathogens are more prevalent. The risk factors or subclinical mastitis appear to be season, herd location and trimester of pregnancy [31].

In India, the dairy industry is facing a great problem due to high prevalence and incidence of mastitis in milch animals. The infection rate of mastitis in cows with pendulous udder is higher than those with non-pendulous udder [32]. The pendulous udder exposes the teat to injury, and pathogens may easily adhere to the teat and get access to the gland tissue. The infection rate in cows with teat lesions is more than cows with normal teats. Cows with disk shaped, inverted, pointed and round shaped teat ends have 88.46, 61.54, 54.17 and 40.86% rates of infection, respectively [33].

In India, subclinical mastitis was found more important (varying from 10-50% in cows and 5-20% in buffaloes) than clinical mastitis (1- 10%). The incidence was highest in Purebred Holsteins and Jerseys and lowest in local cattle and buffaloes. An investigation on 250 animals from periurban farms indicated that the monsoon season was more prone to subclinical mastitis than summer or winter, prevalence increased with higher lactation number and animals in 4th-5th month of lactation were found more susceptible (59.49%), hind quarters were found more affected (56.52%) than fore quarters (43.47%). The factors like herd size, agro-climatic conditions of the region, variations in socio-cultural practices, milk marketing, literacy level of the animal owner, system of feeding and management were found important affecting the incidence of subclinical mastitis [34].

Pathogenesis of Bovine Mastitis

There is evidence that pathogens use various mechanisms to impinge upon cell death pathways. A number of pathogens are armed with an array of virulence determinants, which interact with key components of a host cell’s death pathways or interfere with regulation of transcription factors monitoring cell survival. These virulence factors induce cell death by a variety of mechanisms, which include 1) Pore-forming toxins, which interact with the host cell membrane and permit the leakage of cellular components; 2) Toxins that express their enzymatic activity in the host cytosol; 3) Effector proteins delivered directly into host cells by a highly specialized type-III secretory system; 4) Superantigens that target immune cells, and 5) Other modulators of host cell death [35]. Much progress has been made in understanding the role of apoptosis and necrosis in response to bacterial infection.

A comprehensive understanding of the pathogenicity of mastitis is a key for the development of appropriate detection techniques. The primary cause of mastitis is a wide spectrum of bacterial strains; however, incidences of viral, algal and fungal-related mastitis were also reported [36].

Normally, the teat canal is tightly closed by sphincter muscles, preventing the entry of pathogens. It is lined with keratin, a waxy material derived from stratified squamous epithelium that obstructs the migration of bacteria and contains antimicrobial agents, such as long-chain fatty acids, that assist in combating the infection. However, the efficiency of keratin is restricted [37,38]. Fluid accumulates within the mammary gland as parturition approaches, resulting in increased intramammary pressure [38] and mammary gland vulnerability caused by the dilation of the teat canal and leakage of mammary secretions [39]. Additionally, during milking, the keratin is flushed out and there is distention of the teat canal [40]. The sphincter requires about 2 hour for returning back to the contracted position [37].

Once inside the teat, bacteria must also elude the cellular and humoral defence mechanisms of the udder [39]. If they are not eliminated, they start multiplying in the mammary gland. They liberate toxins and induce leukocytes and epithelial cells to release chemoattractants, including cytokines such as tumour necrosis factor-α (TNF-α), interleukin (IL)-8, IL-1, eicosanoids (like prostaglandin F2α), oxygen radicals and acute phase proteins (APPs) (e.g. haptoglobin, serum amyloid A). This attracts circulating immune effector cells, mainly polymorphonuclear neutrophils (PMNs), to the site of infection [41-43].

PMNs act by engulfing and destroying the invading bacteria via oxygen-dependent and oxygen-independent systems. They contain intracellular granules that store bactericidal peptides, proteins, enzymes (such as myeloperoxidase) and neutral and acidic proteases (such as elastase, cathepsin G, cathepsin B and cathepsin D) [44,45]. The released oxidants and proteases destroy the bacteria and some of the epithelial cells, resulting in decreased milk production and release of enzymes, such as N-acetyl-b-D-glucosaminidase (NAGase) and Lactate Dehydrogenase (LDH). Destruction of most of the PMNs takes place by apoptosis once their task is fulfilled. Subsequently, macrophages engulf and ingest the remaining PMNs [46,42]. The dead and sloughed off mammary epithelial cells, in addition to the proteinases and dead leukocytes, are secreted into the milk, resulting in high milk SCCs (Somatic cell count) [47,48].

If the infection persists, internal swelling within the mammary epithelium, not normally detectable by an external examination, can occur. The mammary gland alveoli become damaged and start losing anatomical integrity. The blood-milk barrier is breached, causing extracellular fluid components, such as chloride, sodium, hydrogen, potassium and hydroxide ions, and plasminogen to enter the gland and mix with the milk [49,43].

When extensive damage to the blood-milk barrier has occurred, blood might be detected in the milk. This leads to visible changes on the udder, such as enhanced external swelling and reddening of the gland. Changes also occur in the milk, including increased conductivity, increased pH, raised water content and the presence of visible clots and flakes [50,43]. This marks the initial stage of clinical symptoms, and the most severe infections might ultimately result in the death of the animal.

Factors Influencing Susceptibility of Mastitis

Mastitis is a difficult problem to comprehend because it is a disease caused by many factors. Microorganisms are responsible for the infection, but for them to enter the mammary glands and establish themselves to the point that they cause an infection, a multitude of factors may be involved. There are many such factors (e.g. hygiene, housing, climate, milking machines, feed, genetics) acting simultaneously. It is even more difficult to generalize about the relative importance of each one, as certain factors affect certain microorganisms in particular.

There are Several Factors Which Affect Prevalence of Bovine Mastitis Which is As Under

Animal factors

It includes the presence/absence of natural resistance to mastitis, the state of defense mechanisms (are the present and are they functional), the stage of lactation, and whether there are stress factors.

Physiological factors

Age and stage of lactation: Both quarter infections and clinical mastitis occur increasingly with the age of lactation and there are more chances of occurrence at the first lactation.

Milk yield: Incidence of mastitis is higher in high yielding bovines. Fast milking also promotes occurrence of mastitis.

Morphological characteristics of the udder and teat: Cows with the most pendular-shaped quarters appear to be the most susceptible to mammary infections. Similarly, long teats increase the risk of accidental trauma and these lesions constitute potential sources of microorganisms which increase the probability of quarter infection.

Teat resistance mechanisms

Influence of length and diameter of teat canal: Length and diameter of teat canal does not influence susceptibility towards infection but faster milking rates increases susceptibility.

Bactericidal activity of keratin: The keratin lining of the teat canal is considered as an important factor in protection against infection.

Organism Factors

It includes the number of organisms in the gland, the pathogenicity of the organisms (they must penetrate the gland, then adhere to the tissue, and then reproduce), the presence of other virulence factors, and the state of the host defenses for resistance to infection.

Environmental Factors

It includes the design and function of milking machine, the milking environment, the milking hygiene practices, the type of housing and bedding, and the weather.

Milking machine

Improper use of milking machine (irregular fluctuation of vacuum level, over-milking and incomplete milking) is related to tissue irritations and incidence of mastitis.

Season and Housing

Mastitis often increases when cows are turned onto pastures. Chilling of the udder in cold ground in the spring or fall. Housing as it relates to the degree of udder and teat injury.

Clinical Characteristicas Bovine Mastitis

Mastitis caused by Staphylococcus aureus

The chronic and subclinical forms predominate and on a herd basis, are the most important. S. aureus bacteria produce toxins that destroy cell membranes and can directly damage milk-producing tissue. White blood cells (leukocytes) are attracted to the area of inflammation, where they attempt to fight the infection. Initially, the bacteria damage the tissues lining the teats and gland cisterns within the quarter, which eventually leads to formation of scar tissue. The bacteria then move up into the duct system and establish deep-seated pockets of infection in the milk secreting cells (alveoli). This is followed by the formation of abscesses that wall-off the bacteria to prevent spread but allow the bacteria to avoid detection by the immune system. The abscesses prevent antibiotics from reaching the bacteria and are the primary reason why the response to treatment is poor [51].

However, bacteria can also escape the killing effects of some antibiotics by hiding within neutrophils (white blood cells) and other host cells. As the neutrophils attempt to remove bacteria, many organisms survive and become dormant within them, preventing contact with antibiotics. When the white blood cells die (usually in one to two days) the bacteria are released to resume the infection process [51].

During infection, destruction of alveolar and ductal cells reduces milk yield. These damaged cells may combine with leukocytes and clog the milk ducts that drain the alveolar areas, contributing to further scar tissue formation, occlusion of ducts, and decreased milk production. The ducts may reopen at a later time, but this usually results in a release of S. aureus organisms to other areas of the mammary gland. The spread of S. aureus within the gland results in the formation of additional abscesses that can become quite large and detectable as lumps within the udder [51].

Though most cases of S. aureus mastitis are subclinical, chronic cows usually have high SCC, abnormal mammary tissue, and recurrent cases of clinical mastitis. Clinically infected quarters often show moderate swelling and visible clots (chunks) in the milk, especially in fore strippings. Acute S. aureus infections generally develop late in the lactation. However, the clinical symptoms (udder swelling or hardness, changes in appearance of milk) do not show up until calving or early in the next lactation [51].

Mastitis Caused by Streptococcus dysgalactiae

Str. dysgalactiae is generally characterized as an environmental pathogen, but also may have characteristics of a contagious organism and appears to spread from cow to cow. This pathogen is generally responsive to teat dipping and dry cow therapy, but new infections can occur in a herd when no other udder infections by this organism are present [52]. Teat damage caused by contamination with sand or grit, or poorly operating milking machines is prime reasons for Str. dysgalactiae mastitis.

Mastitis Caused by Streptococcus Agalactiae

Str. agalactiae is slowly progressive over time, causing fibrosis and atrophy of the affected quarter. In later stages, the acini become filled with scar tissue which plugs the glandular-ductal system resulting in a chronic, smoldering infection which decreases milk production and increases the somatic cell count (SCC) of the quarter.

Mastitis Caused by Corynebacterium Bovis

Corynebacterium bovis is considered a minor pathogen. The main reservoir appears to be infected udders or teat ducts, and this organism is spread rapidly from cow to cow in the absence of adequate teat dipping. Infections by C. bovis cause only moderate inflammation with SCC exceeding those of uninfected glands by only two- to threefold. Infections are infrequently the major cause of elevated bulk tank SCC, clinical mastitis, marked compositional changes, or dramatic decreases in milk production [52].

Mastitis Caused by Streptococcus Uberis

Str. uberis mastitis can spread from cow-to-cow at milking [53]. It usually results in non-specific signs of mastitis which include swelling, oedema and firmness of the udder with clots or flakes in the milk. The milk also appears more watery than normal.

Mastitis caused by Staphylococcus Pyogenes

S. pyogenes produces a very acute type of mastitis accompanied by severe systemic disturbances and fever. Animal dies in a few days and gangrene may occur [54].

Mastitis Caused by Corynebacterium Pyogenes

C. pyogenes is the cause of ‘summer mastitis’ affecting both immature and lactating glands. It produces large amount of pus resulting in to abscess. There may be fistula discharging the pus to exterior as well as large scale necrosis and sloughing. In later stage, thrombosis and fibrosis with loss of function occurs [54].

Mastitis Caused by E.coli

The final outcome of E. coli mastitis (Coliform mastitis), as rapid elimination of bacteria, prolonged infection or death of the cow due to endotoxin shock, describes more the ability of the cow to limit deleterious inflammatory reactions and to clear the infection [25]. E. coli mastitis typically has a sudden onset, which leads to changes in milk appearance, first to serous and yellow, and later to clotty and thick. Milk SCC increases to very high numbers. The udder becomes hard, swollen and tender. The cow also has systemic signs, generally including high fever, increased pulse frequency, reduced rumen contractions, lack of appetite, depression and decreased milk production. Studies using experimental E. coli mastitis models have shown that the first signs are usually noticed at the local level, at approximately 8 h post-challenge, and fever and other systemic signs peak at 12 h post-challenge [55,56]. In mild or moderate cases, the systemic signs vanish within 48 h and local signs within 7 days [57,55]. In severe cases, the cow may not survive or systemic signs may be prolonged, with milk production being lost permanently [55,58].

Mastitis Caused by Cryptococcus Neoformans

It is a surgical infection that may be encountered by repeated intramammary infusions. C. neoformans produces an acute inflammatory reaction. One or more quarters may be affected. The milk turns to a watery, flaky secretion. The gland is fleshy and interlobular septa are distended with edema. There is large scale destruction of the glandular tissue and, the alveolar and ductal epithelium is liquefied to form a viscid, mucoid material. In sections, the double refractile fungus can be seen in the large numbers, some of which are found engulfed by the histiocytes. In chronic cases, granulomatous nodules with interlobular and intralobular fibrosis occur together with infiltration by histiocytes and lymphocytes [54].

Gangrenous Mastitis

S. aureus, E. coli and Clostridium perfringens have predominated in causing gangrenous mastitis in ruminants [59,60]. In severe cases of mastitis, virulent strains produce thrombosis of mammary vessels resulting into infarction and gangrene. Usually all the four quarters are affected. The udder becomes cold and bluish within 3-4 days after infection. In many cases death may supervene [54].

Mastitis Caused by Brucella Abortus

Late gestation abortion is the predominant clinical sign of B. abortus infection in cows, resulting in reproductive failure and consequently a decrease in milk production [61]. Usually, there are no gross lesions in the mammary glands [62,63]. Histologically, it produces intralobular granuloma which consist lymphocytes, plasma cells, histiocytes and a few Langhans type giant cells [54].

Mastitis Caused by Mycoplasma Spp

Cows of all ages are affected. All four quarters may be involved, with sudden drop in milk yield. There is cessation of lactation and the animal will not be useful again for dairy purposes. Purulent mastitis occurs and the organism may also invade the blood and, then joints resulting into arthritis with swelling of the joints and lameness. Milk becomes abnormal grossly and it is thick, cheesy and tinged with blood. The udder is swollen and later it gets atrophied [54].

Mastitis caused by Prototheca zopfii

Mastitis caused by P. zopfii is most often recognized as a chronic, symptom-less process with very high SCC; however, acute, clinical mastitis may also occur [64]. The tissues of the lactating udder are highly susceptible to P. zopfii infection. In acute cases, the sero-purulent form of mastitis can be observed with large numbers of alga cells in milk, in the alveolar epithelial layer, in macrophages, and in the interstitium. Pronounced proliferation of interstitial connective tissue and concurrent atrophy of alveoli characterize chronic cases. As compared to mastitis of bacterial origin, in mastitis due to algae infiltration of the udder tissue with mononuclear cells is more pronounced [65].

Diagnosis of Bovine Mastitis

Early diagnosis is of the utmost importance due to the high costs of mastitis. Diagnostic methods have been developed to check the quality of the milk through detection of mammary gland inflammation and diagnosis of the infection and its causative pathogens. Currently, assays often used include measurement of SCCs, enzymatic analysis, California Mastitis Test (CMT), Bromo Thymol Blue (BTB), modified whiteside test, trypsin inhibition test, milk pH, and electric conductivity [36,34]. Colourimetric and fluorometric assays have been developed for measuring the concentrations of enzymes elevated in milk during mastitis (e.g. NAGase or LDH). Use of culturing techniques for the detection of mastitis-causing microorganisms is still the gold standard, although it is very labor-intensive and therefore expensive.

Somatic Cell Count (SCC)

Milk SCC is the most used indirect indicator of subclinical mastitis [66]. Two systems for on-line SCC analysis of milk are currently available:

Direct method

Dyeing the nuclei of somatic cells and counting them automatically from a photo. Milk samples are taken from the cow composite milk.

Indirect method

Hydrolyzing the DNA of the nuclei of somatic cells and measuring the viscosity of the compound. The milk sample is taken from the first fraction of the milk after milk ejection has started. This method operates at quarter level.

However, usually and in the study of Mollenhorst et al. [67], when foremilk samples are taken after milk ejection, they should be quite representative of the quarter composite milk, at least with SCC 50000- 300000 cells/ml [68].

California Mastitis Test (CMT)

The California Mastitis Test (CMT) is used on farms to identify subclinical mastitis by an indirect estimation of the SCC in milk [69]. A bromocresol-purple-containing detergent is used to break down the cell membrane of somatic cells and the subsequent release and aggregation of nucleic acid forms a gel-like matrix with a viscosity that is proportional to the leukocyte number. It is cost effective, rapid, user friendly and can be used ‘on-site’ or in the laboratory. It can be difficult to interpret and has low sensitivity [4].

Milk Color

Milk color changes during clinical mastitis and physical damage of the udder as blood constituents leaks from the vessels. A sensor measuring reflected light intensity can be used to measure milk colour and detect abnormal milk [70] and blood in the milk [71]. This colour sensor analyzed a continuous flow of milk in automatic milking and detected blood in the milk at concentrations as low as 0.1%. The conventional visual method using a black strip cup, detected only minimum of 2.0% of blood in the milk [72]. Green and blue colors were the best indicators for abnormal milk and clinical mastitis, although they did not correlate well with the appearance of the milk [73].

Portacheck

This assay uses an esterase-catalysed enzymatic reaction to determine the SCC in milk. It is cost effective, rapid and user friendly. It is having low sensitivity at low SCCs [4].

Fossomatic SCC

This counter operates on the principle of optical fluorescence.Ethidium bromide penetrates and intercalates with nuclear DNA, and the fluoresecent signal generated is used to estimate the SCC in milk. It is rapid and automated. The device is expensive and complex to use [4].

Delaval Cell Counter

This counter operates on the principle of optical fluorescence, whereby propidium iodide is used to stain nuclear DNA to estimate the SCC in milk. It is rapid and the device is easily transportable. It is relatively expensive [4].

Electrical Conductivity (EC) Test

EC has solely been used for detection of bovine mastitis on the phenotypic level [74]. This test 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. It can be used ‘on-site’. Non-mastitis-related variations in EC can present problems in diagnosis [4].

Culture Tests

Laboratory-based tests use selective culture to identify different microorganisms involved in causing mastitis. It identifies specific pathogens causing mastitis. It cannot be used ‘on-site’ and the waiting time for results can be days [4].

pH Test

The rise in milk pH, due to mastitis, is detected using bromothymol blue. It is user friendly, cost effective and rapid. It is not as sensitive as other tests [4].

Biomarkers

Biomarkers are used to detect enzymes, such as Serum Amyloid A (SAA), Haptoglobin (Hp), Lactate Dehydrogenase (LDH), N-acetyl- β-d-glucosaminidase (NAGase) and Alkaline Phosphatase (AP). Each of these parameters are valuable in order to detect changes in the milk indicating mastitis [75]. These assays are rapid. These assays might be laboratory-based [4].

Proteomic Techniques

Advances in relevant proteomics techniques, such as twodimensional gel electrophoresis (2D-GE) and mass spectroscopy (MS) [76-78], have led to the identification of several new proteins involved in mastitis. They could potentially be used as markers for its detection, as reduced neutrophil function has been correlated with mastitis [76]. The results showed that there is an up regulation of k-casein and a down regulation of cytochrome C oxidase and annexin V in animal tissues that are mastitis-infected [79].

Immunoassays

Numerous immunoassays have been developed for the detection of pathogens in milk [80-83] and are used for monitoring milk quality. More than one hundred known organisms can be responsible for causing mastitis [84], but ELISAs have only been developed for some of the most prevalent pathogens, such as S. aureus, E. coli and Listeria monocytogenes. Multiplex PCR and ‘real-time’ PCR assays that can simultaneously detect different mastitis-causing organisms in milk samples have been described [85,86], and the most recently developed assay is capable of detecting 11 of the major mastitis-associated pathogens, including E. coli, S. aureus, Streptococcus agalactiae and Streptococcus uberis [87].

Infra-Red Thermography

Infra-red thermography (IRT) is a non-invasive method for measuring radiated heat emitted by the skin that reflects subcutaneous circulation and metabolism [88]. Radiated heat emitted by the udder during clinical mastitis can be detected with IRT. IRT is not related to milking or milk itself, which provides a possibility for detecting mastitis during the dry period and before the first calving.

Berry RJ, [89], developed a predictive model for the temperature of the udder surface based on consecutive measurements of healthy cows and ambient temperature. They concluded that IRT showed promise for early detection of mastitis. IRT was not suitable for detection of subclinical mastitis [90]. Preliminary studies on the detection of clinical mastitis using IRT have shown promising results [91,92].

Prevention and Control of Bovine Mastitis

The prevention and control of bovine mastitis can be achieved by

Proper milking hygiene

Bacteria transmit to the uninfected from the contaminated hands of the milker. Thus the milker's hands should be washed thoroughly with disinfected soaps before milking and clinically infected cows should be milked last. Teats should be cleaned and dried before milking.

Milking machine

It should function and operate properly. 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 regularly. Cows are also exposed to mastitis organisms via the milking machine when milked after a cow affected with clinical or sub clinical mastitis.

Dipping the teats after milking

After milking, the sphincter muscle surrounding the teat canal remains dilated for a varying period of time facilitating invasion of the teat canal by bacteria. Thus teat dips are most effective when applied immediately after milking machine is removed. Teat dipping does not reduce existing infection. However, the rate of new infection can be reduced by up to 50% when suitable disinfectant is used to immerse or spry the teats. Post milking teat dipping with a germicidal (germkilling) dip is recommended. Barrier dips are reported to reduce new coliform infections; however, they do not appear to be as effective against environmental streptococci and the contagious pathogens.

Dry cow treatments

Incidence of mastitis during the dry period can be considerably reduced by effective use of antibiotic infused in each quarter of the udder at the last milking of lactation. Dry cow therapy is the best way to cure chronic and subclinical mastitis that are difficult to treat successfully during lactation. Recommended for all quarters of all cows at drying off and helps in controlling environmental streptococci during the early dry period.

Culling of chronically infected cows

This is an effective method because in most herds only 6-8% of all cows account for 40-50% of all clinical mastitis. Culling cows for mastitis is effective in eliminating mastitis in the herd.

Nutrition

Deficiencies of selenium and vitamin E in the diet have been associated with an increased rate of new mammary infections. Proper nutrition will reduce the risk of environmental mastitis. Adequate levels of Vitamin E and selenium reduce the incidence of environmental mastitis.

Environment

Cow environment should be as clean and dry as possible. Cow should not have access to manure, mud, or pools of stagnant water. Dry cow environment is as important as lactating cow environment. Calving area must be clean. Properly design and maintain free stalls.

Bedding

Bacteria numbers in bedding depends on available nutrients, amount of contamination, moisture, and temperature. Inorganic materials (such as crushed limestone or sand) are low in nutrients and moisture, and thus bacteria. Finely chopped organic bedding (such as sawdust, shavings, recycled manure, pelleted corncobs, various seed hulls and chopped straw) is frequently high in bacteria numbers.

Vaccines

Development of vaccines for bovine mastitis has been difficult and even natural intramammary infection does not provide protection against subsequent infections [93]. 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 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. 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 (eg. from Protein A) and injected intramuscularly or into the area of the supramammary 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.

Use of backflush

Backflushers have been developed to sanitize the liners and claws between milkings. Most units on the market have four or five cycles. The first cycle is a water rinse, followed by iodine or similar sanitizer rinse, a clear water rinse, and positive air dry cycle. Research has demonstrated that backflusher reduces the number of bacteria on the liners between cows, but do not reduce the number of bacteria on teats. Backflushers also may stop the spread of contagious organisms, but this can also be accomplished at a much lower cost by teat dipping. There is no effect on environmental pathogens that are encountered between milkings.

Treatment of Bovine Mastitis

Cows are constantly exposed to bacteria from external sources and subclinical infections are commonly found in 50-70% of most herds. At the end of lactation, existing infections remain in the udder and, after the subsequent calving; the subclinical level of mastitis may be significantly higher than during the previous lactation. Antibiotics can be used at two points in this cycle of infection: (a) To treat outbreaks of mastitis in milking cows as soon as they occur, and (b) To reduce subclinical infection during the dry period and hence increase the cow’s productive life [2].

Acute mastitis such as that caused by coliform bacteria endangers the cow’s life and requires immediate attention of a veterinarian. Milking the affected quarter every 2-3 hours helps to eliminate toxins. Treatment of clinical mastitis limits the duration and possible spread of the disease. Only mastitis caused by S. agalactiae can be treated successfully with antibiotics during lactation. The success rate of antibiotics in treating mastitis cause by S. aureus and coliform bacteria does not exceed 50% could be as low as 10%). Subclinical mastitis (high SCC in milk) should not be treated with antibiotics during lactation and they are treated at the time of drying off. Pre-partum intramammary antibiotic therapy for heifers reduced the number of coagulase negative Staphylococcus (CNS) infections during first lactation, but the effect on SCC was variable [94,95].

Antibiotic treatment

Typically when clinical mastitis is detected, the cow is milked out and then given an intramammary infusion of antibiotic directly into the infected gland. Clinical mastitis symptoms 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, a quarter that is swollen or hot to the touch.

The most commonly used antibiotics on conventional dairies were penicillin (86%), cephalosporin (78%), and tetracyclines (41%). Almost all dairymen treated calves with respiratory conditions and the most often used antibiotics were tilmicosin, ceftiofur, penicillin and florfenicol. Nearly 80% of the dairymen used antibiotics to treat calves with diarrhea and they commonly used trimethoprim-sulfa or tetracyclines. Nearly all dairymen also used antibiotics to treat adult cows with respiratory conditions (97%) and to a lesser extent mastitis (80%), metritis (80%) and foot problems (83%). Ceftiofur (80%) was by far the common antibiotic used to treat respiratory disease followed by tetracyclines (31%) and penicillin (32%). For mastitis, penicillin (42%), ampicillin (26%) and tetracyclines (18%) were commonly used. 98% of the conventional dairy herds used intramammary dry cow antibiotic treatment while only 6.3% of the organic herds used intramammary dry cow therapy. The organic herds used non-antibiotics products for dry cow therapy. Table 1 is showing classification of antibacterial drugs according to their potential distribution throughout the udder after parenteral and intramammary administration [2].

Table 1: Classification of antibacterial drugs according to their potential distribution throughout the udder after parenteral and intramammary administration.

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.

Economics of Bovine Mastitis

Mastitis is an expensive disease on dairy farms, with a large difference in economic losses between farms, indicating that for a large proportion of farms there are many avoidable losses [96]. Economic costs of mastitis, as with other diseases, consist of losses, such as less milk production per cow per year, and expenditure, such as extra use of antibiotics [97]. Expenditure also consists of that for preventive measures. Many factors make up the costs of mastitis. Those most commonly consists decreased milk production, veterinary services, diagnostics, drugs, discarded milk, labour, decreased product quality, increased risk of new cases of the same disease or of other diseases, increased risk of culling, and materials for prevention [98]. Although the costs of factors differ between countries and between regions, the economic principles behind them are the same [98-100].

Conclusion

Bovine mastitis remains a complex disease and its management is an increasing challenge during the last 30 years when many studies have been made in an attempt to more fully describe the extent and nature of this problem worldwide. The control strategies led to reduce the incidence of disease and the prevalence of infection in the mammary gland of dairy cow. The progress has been made to a great extent by the use of therapeutic and prophylactic antibiotics treatments. But there is resistance problem against many antibiotics due to concurrent change in the etiology of bovine mastitis. Similarly, there is also the problem of the efficacy and cost-effectiveness for the prophylactic application of intramammary antibiotic. In future, these challenges provide an opportunity to researcher and clinician to study the organism’s adaptation to changing environments, reduce antibiotic usage, fast and reliable diagnostic techniques with cost-economy.

References