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Mastitis in dairy cattle
Mastitis (Mast: breast, itis: inflammation) is defined as an inflammatory reaction of udder tissue to bacterial, chemical, thermal or mechanical injury. Mastitis may be infectious caused by microbial organisms or noninfectious resulting from physical injury to the gland. The inflammatory response consists of an increase in blood proteins and white blood cells in the mammary tissue and the milk. The purpose of the response is to destroy the irritant, repair the damaged-tissue and return the udder to normal function.
Development of the disease
Mastitis begins after bacteria pass through the teat duct and enter the cisternal area. Invasion of the teat usually occurs during milking.Organisms present in the milk or at the teat end enter the teat canal and cistern when there is admission of undesired air in unit. After milking, the teat canal remains dilated for 1-2 hours while the canal of a damaged teat may remain partially open permanently. This makes it easier for organisms from the environment or those found on injured skin to enter the teat canal.
Adherence of bacteria to tissues lining cisterns and ducts may prevent flushing-out during milking and help establish infections. Bacteria eventually enter the glandular tissues where they affect alveolar cells. Toxins produced by bacteria cause death of or damage to milk-secreting epithelial cells, and these cells produce substances to the blood stream that increase blood vessel permeability. This allows leukocytes to move from the blood into the alveolus where they function by engulfing bacteria.
Types of mastitis
A- Contagious Mastitis: 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.
B- Environmental mastitis: Describes mastitis caused by organisms such asEscherichia 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.
Contagious mastitis can be divided into three groups:
1- Clinical mastitis
2- Sub-clinical mastitis
3- Chronic mastitis
Characterized by the presence of gross inflammation signs (swelling, heat, redness,pains). Three types of clinical mastitis exist.
1.1- Peracute mastitis
Characterized by gross inflammation, disrupted functions (reduction in milk yield, changes in milk composition) and systemic signs (fever, depression, shivering, loss of appetite and loss of weight).
1.2- Acute mastitis
Similar to percute mastitis, but with lesser systemic signs (fever and mild depression).
1.3- 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 california mastitis test
An 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 may exhibi periodical flare-ups sub-acute or acute form, which last for a short period of time.
Bacteria that most frequently cause mastitis can be divided into two large groups based on the source of the bacteria: contagious pathogens and environmental pathogens. The primary contagious pathogens areStreptococcus agalactiae, Staphylococcus aureus and Mycoplasma species.
Primary environmental pathogens include two types of bacteria: coliform bacteria and species of streptococci other than Strep. agalactiae. These other streptococci are referred to as the "environmental streptococci".The primary source of environmental pathogens is the surroundings in which a cow lives. The sources of contagious mastitis, however, are infected cows and transmission is from cow to cow. Therefore, methods of control developed for the contagious pathogens are not effective against environmental pathogens.
S. agalactiae is the most common cause of subclinical mastitis but rarely cause acute mastitis. The organism lives inside the cow's udder and survives only for a short time outside the mammary gland. It spreads primarily during milking via the milking machine, and contaminated hands and materials (cloths). The microorganism can be eradicated from the herd by appropriate treatment combined with good milking practices S. aureus lives inside and outside the udder on the teat skin. The microorganism can cause both clinical and sub-clinical mastitis and spreads the same way as S. agalactiae.
Yeast can also cause mastitis. Overuse of antibiotics and poor sanitation contribute to yeast mastitis.
The relationship of environment, microorganism and environment contribute to mastitis
Inflammation is characterized by- Gross abnormalities in the udder (swelling, heat, redness, pain). Persisting inflammation leads to tissue damage and replacement of secretory tissues with of the udder with nonproductive connective tissues.
Change in composition and appearance of milk. Abnormalities in milk mayinclude flakes, clots or a watery appearance. The flakes in the milk are congealedleukocytes, secretory cells and protein. The most significant loss of milk is the composition of the fat that i greatly reduced compared to normal milk.
A lower milk yield.
Inflammation of the infected udder of a cow
Left: abnormal milk vs normal milk
The first step in treating mastitis is to identify the causative agent. The presence of a pathogen and the inflammatory response of the udder signify an infection. The inflammatory response, which results in abnormal milk is usually detected by the dairyman.
There are few test to diagnose mastitis in farm
1. The stircup test
The stircup test
The stripcup or strip plate is an important in the milking parlor for determining the presence of clinical mastitis. The test is rapid and can easily be adapted as a part of milking routine. Few streams of the foremilk are squirted onto the strip cup and are visually examined for milk abnormalities.
The stripcup test should be conducted on every cow at every milking and milk from any cow found to have abnormal milk should be withhold from the supply. In addition to the identification of clinical mastitis, the use of the stripcup has other benefits. The stripping of the first streams of milk stimulates milk let-down, resulting in a faster milk out which can result in a shorter milking time. Removal of the foremilk may reduce bacterial contamination of the milking machine and thus reduce the probability of udder contamination and enhance the quality of milk produced.
2. The California mastitis test
The CMT estimates the number somatic cells present in the milk. The CMT is conducted by mixing the test reagent with an equal quantity of milk. It reacts with materials from the nuclei of the somatic cells in the milk to form a gel. The reaction is then visually scored depending on the amount of gel formed (Table 3).
The CMT is a simple, inexpensive, rapid screening test and is useful in determining which quarter of the cow is most affected. However, the CMT can not be used as a means of picking out cows for treatments as it all detects is a cellular response to inflammation. The test is useful in indicating sub-clinical and chronic mastitis.
The california mastitis test
3. Wisconsin mastitis test
4. Somatic cell count
Factors influencing susceptibility to mastitis
1. Type of bacteria: Some bacteria are more virulent than others in causing mastitis.
2.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 tomastitis. It is likely that intramammary pressure is a predisposing factor for mastitis during these periods.
3. 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.
4. 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.
5. Inherited features of the cow: Length of the leg in proportion to the udder size and relative strength of the udder attachment are examples. Large, pendulous udders tend to exceed the capacity of the supporting ligaments, with a consequent of breakdown of the udder. This will subject the udder to more physical injuries and thus increases the incidence of mastitis.
6. Milking machine: Improper use of milking machine (irregular fluctuation of vacuum level, over-milking, incomplete milking) is related to tissue irritations and incidence of mastitis.
7. 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.
Antibiotic treatment: Typically when clinical mastitis is detected, the cow is milked out and then given an intramammary infusion of antibiotic, ie. infused directly into the infected gland.
Intramammary infusion technique
Apply antibiotics directly into the udder. The following antibiotics can be infused through teat canal:
Penicillin at a dose rate of 50 - 200,000 units
Tetracycline at a dose rate of 100 - 400 mg
Streptomycin at a dose rate of 0.25 - 1 g
Neomycin at a dose rate of 0.5 - 1 gPolymixin at a dose rate of 50 mg
Erythromycin at a dose rate of 300 - 600 mg
How to apply antibiotic directly into the teat:
Step 1: Milk the udder until it is empty
Step 2: Clean the end of the teat
Step 3: Put the tip of the tube into the teat and squeeze the antibiotic up into the udder
Step 4: Massage the teat and the udder
If the disease is severe, also give antibiotics by injection!
The following drugs can be used
Penicillin at 5 million units every 12 hours
Tetracycline at 1 - 3 g every 24 hours
Streptomycin at 10 - 11 mg per kg body weight every 24 hours
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.
Control and prevention
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 backflushing). Individual 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.
Post-milking teat dipping with a germicide
Intramammary infusion with dry cow antibiotic therapy at drying off of the cow.
Use of individual paper towels to wash and dry teats before milking.
Proper milking machine function is necessary for control of contagious mastitis.
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.
Dirty, unclipped udder can contribute to environmental mastitis.
|Clipped, clean udder.|
Bedding of stalls is important to minimizing environmental mastitis.
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.
Sources: Mastitis case studies.ilinois.edu; Merk's veterinary manual 10th edition, mastitis;wikipedia, infobet-biovision.org, mastitis in dairy cow; macdonald campus of Mcgill university