PATHOGENESIS AND DIAGNOSIS OF MASTITIS IN DAIRY CATTLE
Poobitha S*., Sathish Kumar M., Uma S., Kumar R
Department of Veterinary Pathology, Rajiv Gandhi Institute of Veterinary Education and Research, Puducherry-605 009, India.
ABSTRACT
Mastitis is an inflammatory conditions affecting mammary gland. It is the most common disease in dairy cattle. It is one of the most economically important diseases in dairy industry. Milk from cows suffering from mastitis can cause a public health risk due to an increased somatic cell count. Mastitis results when white blood cells (leucocytes), are released into the mammary gland in response to an invasion of bacteria. The toxins released by the bacteria will damage the milk-secreting tissues and various ducts throughout the mammary gland. Mastitis can also occur as a result of chemical, mechanical, or thermal injury.
KEY WORDS: Dairy cattle, Mammary gland, Milk, Diagnosis
INTRODUCTION
Mastitis is an inflammatory change of the mammary gland along with physical, chemical, and microbiological changes, and is characterized by an increase in somatic cells especially leucocytes in the milk. It is a common disease among dairy cows worldwide.It may affect one or all quarters of the udder. If one quarter is affected 25% milk yield is lost permanently. It may also spread to other quarters, hence it causes major economic losses to the farmer. High-yielding animals are more prone to this condition, if not milked properly. The milk from infected udders contributes to high microbial counts of milk, which in turn is not suitable for the preparation of milk products.
CLASSIFICATION OF MASTITIS
Mastitis is often associated with bacterial intramammary infections (IMI) and is subdivided into clinical mastitis (inflammation with visual signs of inflammation in the udder or milk; CM) and subclinical mastitis (inflammation without visual signs; SCM). Both CM and SCM influence milk quality and yield negatively and mastitis is therefore of major economic concern. Clinical mastitis is characterized by sudden onset, swelling, and redness of the udder, pain and reduced and altered milk secretion from the affected quarters. The milk may have clots, flakes or of watery in consistency and accompanied by fever, depression and anorexia. The sub clinical mastitis is characterized by having no visible signs either in the udder or in the milk, but the milk production decreases and the SCC increases, having greater impact in older lactating animals than in first lactation heifers. Milk from normal uninfected quarters generally contain below 200,000 somatic cells /ml. A value of SCC above 300,000 is abnormal and an indication of inflammation in the udder.
FACTORS INFLUENCING SUSCEPTIBILITY TO MASTITIS
Type of bacteria: Influences the type of symptoms and disease. Some bacteria are more virulent than others in causing mastitis.
Physiological status of cow: Although infection can occurs at any time, most of the new infections take place during the first three weeks of the dry period and during the first month after parturition, suggesting that level of milk production is not directly related to mastitis. It is likely that intramammary pressure is a predisposing factor for mastitis during these periods.
Age of the cow: The incidence of mastitis increases with age. Nevertheless, it is possible for the udder of the first-calf heifer to be infected at parturition.
Level of milk production: Not directly related to incidence of mastitis. However, other factors, which affect milk yield such as milking rates, pendulous udders may be related to mastitis incidence.
Inherited features of the cow: Length of the leg in proportion to the udder size and relative strength of the udder attachment are the examplesof inherited factors that influence the occurrence of mastitis. Large, pendulous udders tend to exceed the capacity of the supporting ligaments, resulting in breakdown of the udder that will ultimately subject the udder to more physical injuries and thus increases the incidence of mastitis.
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.
Environment: 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 are some contributing factors.
PATHOGENESIS
Mastitis in dairy animals occurs when the udder becomes inflamed and bacteria invade the teat canal and mammary glands. These bacteria multiply and produce toxins that cause injury to the milk-secreting tissue, physical trauma, and chemical irritants. These increase the number of leukocytes or somatic cells in the milk, reducing its quantity and adversely affecting the quality of milk and milk byproducts.
The teat end serves as the first line of defense against infection and prevents milk from escaping, and bacteria from entering into the teat.The fibrous proteins of keratin in the teat canal bind electrostatically to mastitis pathogens, which alter the bacterial cell wall, rendering it more susceptible to osmotic pressure and death of invading pathogensDuring milking, bacteria present near the opening of the teat find an opportunity to enter the teat canal, causing trauma and damage to the keratin or mucous membranes lining the teat sinus. The canal of a teat may remain partially open for 1-2 hours after milking and during this period the pathogens may freely enter into the teat canal.
AETIOLOGY AND TYPES OF MASTITIS
Mastitis may be of bacterial or fungal origin.Udder pathogens are often divided into contagious and environmental based on their main reservoirs. Contagious pathogens are well adapted to the cow udder and spread primarily from infected to uninfected mammary glands at milking. In contrast, environmental pathogens readily colonize and multiply in the environment and are usually transferred to the udder from these sources, although transmission from other udders via the milking machine is also possible
The causative organisms of mastitis include Staphylococci, Streptococci, Escherichia coli, Pseudomonas spp., Corynebacterium, Mycoplasma, Streptococcus dysgalactia, and Mycobacterium tuberculosis. Among all the pathogens of bovine mastitis, Staphylococcus aureus is the predominant organism.The most common mastitis pathogens are found either in the udder as contagious pathogens or in the animal surroundings such as bedding and manure soil as environmental pathogens. Among the contagious pathogens, the most common are Staphylococcus aureus and Streptococcus agalactiae. These are spread from infected to clean udders during the milking process through contaminated milker’s hands, cloth towels used to wash or dry udder of more than one animal and possibly by flies. Among environmental pathogens, the most common bacteria are Strepcococcus uberis, Str. dysgalactiae, Coliforms such as E. coli and Klebsiella. Transmission of these pathogens may occur during milking but primarily between milking.
DIAGNOSIS
Mastitis occurs in all species but assumes major economic importance in dairy cattle and buffaloes due to its effect on quality and quantity of milk in high yielders. To avoid these economic losses due to mastitis, it is distinctly important to identify the disease in early stage. Unlike the clinical form, in subclinical form there is neither visual detection of abnormalities in milk nor in mammary gland. Therefore knowledge of routine diagnostic screening tests for early detection of mastitis is desirable to treat the condition and to avoid the subsequent economic losses. The diagnostic method includes:
Physical Examination of Udder
Examination of mammary gland is important for successful detection of mastitis. It is emphasised to view the shape, size, consistency and contour of the udder properly. Detailed examination of the teat and teat orifices should be made to assess inflammation, hot painful swelling and loss of function.
Strip Cup Test
The strip cup or strip plate test is routinely used in milking parlorto detect clinical mastitis. In herd, health management practice operators of the milking machines visually examine the fore milk for gross abnormalities by squirting few stripes of milk on strip cup where the abnormalities are usually manifested in the form of blood, flakes, clots and wateriness suggestive of mastitis.
California mastitis test (CMT)
California mastitis test is simple, inexpensive and rapid screening test. It estimates the number of somatic cells present in milk. In this method mix the test reagent (CMT reagent) with an equal quantity of milk. The reagent reacts with DNA of the nuclei of the somatic cells in the milk to form a gel. The reaction is then visually scored as 0, T (Trace), 1, 2, or 3depending upon the amount of gel formation. Formation of more gel indicates higher somatic cell count.
Modified White Side Test
Increased leukocytic count of milk forms the basis of this test. In mastitis, test shows formation of white flakes, while in normal milk; test result shows formation of milky opaque fluid.
pH Determination Test
The normal pH of milk is 6.4 to 6.8 being isotonic with blood plasma. In mastitis occurring during late lactation and dry period, the concentration of lactose and casein in the milk is reduced whereas sodium chloride and sodium bicarbonate pass into the alveoli from plasma to maintain isotonicity. Therefore during such situations milk becomes alkaline with greater amount of chlorides
Chloride Test
This test detects presence of increased quantity of chlorides in mastitic milk. Normal milk contains about 0.07 per cent of chlorides. Davis (1999) reported that in mastitis there is decreased amount of lactose and increased Page | 79 amount of sodium chloride to maintain the normal milk osmotic pressure hence during inflammation there is increase in the chloride content (> 0.14 per cent).
Electrical conductivity Test
The conductivity of milk may be defined as the property of substances in solution which can ionize and therefore can conduct an electrical current. When the concentration of sodium chloride rises in milk, the conductivity rises proportionately. Therefore, measurement of electrical conductivity is used as a simple physical method to diagnose mastitis.
Methylene Blue Reduction Test (MBRT)
Methylene blue reduction test measures chemical activities, especially the respiratory activites of the bacteria in the milk. The microorganisms in the milk first remove oxygen by respiration and when all oxygen and some other reducible components of the milk has been removed or reduced, there is change in colour of methylene blue to methylene white.
CONCLUSION
Mastitis is a multi factorial disease and continues to be the most important disease of dairy animals as it causes considerable changes in quality and quantity of milk. It also cause economic losses due to reduction of milk yield, decreased milk quality, and higher production costs, medication costs, reduced milk price, increased labour, etc. Many preventive measures include hygienic procedures, antibiotic treatments, teat dipping methods and intra mammary medications can be used. Along with herd management and good sanitation, the selection of animals that are resistant to diseases is a promising alternative approach to reduce the problems caused by the diseases.
*Corresponding author:
S.Poobitha,
Department of Veterinary Pathology,
Rajiv Gandhi Institute of Veterinary Education and Research, Puducherry-605 009, India.
drboovi@gmail.com
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