Causes and clinical signs of mastitis in dairy cows
Mastitis in dairy cows is a serious disease that must never be neglected to avoid its high economic risk factors.
Let's know more about the disease through this article which includes:
- What's mastitis?
- What are the economic risk factors of mastitis in dairy cows?
- Predisposing factors of mastitis in dairy cows.
- Causes of mastitis in dairy cows.
- Sources and route of infection.
- Transmission of mastitis in dairy cows.
- Pathogenesis of mastitis in dairy cows.
- Classification of mastitis in dairy cows.
- General and specific clinical signs of mastitis in dairy cows.
What's mastitis?
It is an inflammation of the mammary gland, characterized by physical, chemical, and bacteriological changes in milk and pathological changes in the mammary gland.
This multifactorial disease is infectious and can affect all animal species.
What are the economic risk factors of mastitis in dairy cows?
Low quality of milk.
Infected milk is not fit for human consumption.
Losses in affected cows.
Lower milk production.
Premature culling of the cow from the herd.
Public health risks due to the microorganisms that are shed in milk, such as:
Streptococcus pyogenes can cause septic sore throat.
Staphylococcus aureus produces enterotoxin which is responsible for food poisoning.
Brucellosis can cause abortion only one or 2 times but can descend in milk along with milking.
Predisposing factors of mastitis in dairy cows
Some factors increase the chance of incidence of mastitis in dairy cows, including:
Age: mastitis more frequently occurs between 7-9 years old.
Stage of lactation: infection increased with the start of the 7th month of pregnancy due to immunity suppression.
The incompleteness of milking: if the milk is left in the udder, it will serve as admirable media for bacterial growth and multiplication.
Presence of immunosuppressive diseases, such as Brucella and bovine leukosis that decreases the power of phagocytic cells of the udder to engulf an invading agent.
Other infectious diseases cause lesions on the udder as FM.D. M.H.C and pox facilitate the weakly invasive microorganism to invade the udder.
Size of the herd: mastitis is much more common in large herds than small herds.
Trauma: horning, hooking, cow steps on her teat or stepped by another cow.
Causes of mastitis in dairy cows
The causative organisms for mastitis in dairy cows can be classified into:
Contagious organisms
These organisms colonize in the mammary gland and have no long existence outside the host.
They usually result in the development of new cases of mastitis within the first two months of lactation.
They spread by milking machines and milkers’ hands.
These organisms include:
Staphylococcus aureus.
Streptococcus agalactiae.
Streptococcus dysgalactiae.
Actinomyces bovis.
Mycoplasma spp.
Environmental organisms:
These organisms do not persist in the udder but have a long existence in the environment.
These organisms include:
Gram-negative organisms such as E.coli, Klebsiella spp., Pseudomonas., (fecal, Contamination).
Fungal organisms such as yeasts.
Sources of infection:
There are 3 main sources of mastitis in dairy cows, including:
Infected udder e.g., Str. agalactiae and Staph, aureus.
Environments e.g., E. coli and Pseudomonas species
Infected milk e.g. Str. pyogenes.
Route of infection:
The dairy cows can be infected through 3 routes, including:
teat canal (especially Streptococcus agalactiae).
After milking, the teat sphincter still opened facilitating the direct invasion of microorganisms into the udder.
Hematogenous as a systemic form of tuberculosis.
The skin covering the gland (staphylococcus).
Transmission of mastitis in dairy cows
The disease can be transmitted through:
Teat cup of the milking machine.
Milkers' hand.
Teat siphon.
Flies.
Pathogenesis of mastitis in dairy cows
The Intramammary infection, which occurs via the teat canal and can be explained in 3 stages, including:
Invasion:
It is a stage in which organisms pass from the exterior of the teat to the milk inside the test canal.
Infection:
In this stage, organisms multiply and invade the mammary tissue.
Inflammation:
It is a stage at which clinical mastitis appears or greatly increased leukocyte content in the milk.
Classification of mastitis in dairy cows
The disease can be classified according to the severity of infection (duration of disease) and the pathology of the udder tissue.
A- Classification according to the severity into peracute, acute, subacute, chronic, and subclinical.
Peracute mastitis:
This form is characterized by:
Marked systemic reactions and toxemia. (42 C).
Sever udder inflammation, e.g., coliform mastitis after parturition.
Abnormal milk secretion.
Acute mastitis:
This form is characterized by:
Mild systemic reactions
(41 C)
Severe inflammation of the udder.
Changes like the milk.
Subacute mastitis
It's characterized by:
No systemic reaction.
Mild inflammation of the udder.
Minor changes in the milk.
Chronic mastitis
It's mainly characterized by:
Changes in milk as the presence of clots or flakes.
Fibrosis and atrophy of the gland, So one quarter becomes smaller than another one.
Subclinical forms:
This form can not be detected clinically.
The milk and the gland appear normal.
It can be detected in the field by using the California mastitis test or agar gel test due to the high leukocyte content of milk,
B- classification of mastitis according to the pathology of the udder tissue.
Catarrhal mastitis
This form of the disease is characterized by:
There are very few of the affected quarters.
The reduction in the milk yield is low.
There are certain physical and chemical changes in the milk.
This condition affects the mucous membrane of the milk sinuses.
It is commonly caused by Staphylococcus and street.
If recognized early, it responds to treatment very easily.
Parenchymatous mastitis with the following affections:
This affects the glandular tissue.
Physical and chemical changes in milk are clear.
Much reduction in milk yield
Interstitial mastitis:
It occurs in aged cows around calving due to the increased interstitial connective tissue between milk acini.
Gangrenous mastitis:
it's the developed form of parenchymatous mastitis.
This is a highly destructive form of mastitis affecting all tissue of the udder.
Bluish discoloration of the udder indicates that gangrenes are setting up.
It is commonly caused by staph. Aureus.
General signs of mastitis:
Mastitis in dairy cows mainly causes general abnormalities in both milk and udder.
The abnormalities in milk include changes in:
Colour as bloody milk.
Viscosity as watery milk or presence of clots and flakes in milk.
Odor as fecal odor.
PH (chemical changes).
The abnormalities of the udder include:
changes in the udder size.
Swelling of the udder may occur due to inflammation.
Atrophy of the gland may develop due to fibrosis.
Changes in udder consistency.
The normal udder is spongy, while the fibrosis udder becomes tender.
Hotness and pain.
Enlargement of supramammary lymph nodes.
Systemic reactions, including fever, toxemia, and anorexia.
II. Specific signs of mastitis:
Each causative agent of mastitis in dairy cows has specific signs, such as :
Streptococcus agalactiae:
It is a common inhabitant of the udder.
It is characterized by fever, udder inflammation, and watery milk (40-41 C).
Staphylococcus aureus:
Severe systemic reaction, toxemia.
Swelling of the udder.
Toxin production causes vasoconstriction resulting in ischemia and the death of tissues leads to gangrene and sloughing of the infected quarter.
The response to antibiotic therapy is poor due to the survival of the organism in macrophages and epithelial cells.
Arcanobacter pyogenes (Summer mastitis):
It is a common inhabitant of the udder tissue.
It causes abscessation in pregnant heifers, dry cows, and lactating cows.
Development of sporadic cases of suppurative mastitis or outbreaks in summer months.
The presence of anaerobes such as Peptostreptococcus indolicus increases the severity of summer mastitis.
Severe systemic reaction associated with swelling the teat and quarter.
The secretion is watery with clots, then purulent with a putrid odor.
The abscesses develop at the base of the text and through the floor of the udder.
Coliform mastitis:
The causative agents are E. coli, Klebsiella spp, and Enterobacter aerogenes.
It is termed environmental mastitis caused by contamination of the udder with bovine feces.
The disease occurs commonly around calving.
Peracute form manifested by systemic reaction and sometimes diarrhea, and death occur due to endotoxemia.
The disease may occur in acute or chronic form.
Tuberculous mastitis (Mycobacterium spp.):
It is a chronic disease of hematogenous origin.
Marked induration and atrophy firstly occur in the upper part of the udder, then involves the entire gland.
Enlargement of the supramammary lymph nodes.
Milk contains very fine floccules, which settle after the milk stand, leaving clear fluid.
Mycoplasma mastitis:
Sudden severe swelling and firmness of all quarters are common.
The milk contains granular deposits in the form of fine sandy materials and flakes.
Complete cessation of milk production may occur.
Some cases are associated with fever and arthritis.
Pasteurella species:
Systemic reaction.
Marked swelling of the udder followed by fibrosis and atrophy of the gland.
Mycotic mastitis:
Cryptococcus neoformans.
Marked swelling of the quarters.
Enlargement of supramammary lymph nodes.
Severe drop in milk production.
The milk becomes viscid, mucoid gray-white secretion.
Candida spp.
Fever.
Severe inflammation of the quarters.
Enlargement of supramammary lymph nodes.
The milk contains large yellow clots in a watery supernatant fluid.
Aspergillus species
Development of multiple abscesses in the quarter surrounded by granulation.
Finally, all the predisposing factors and the causative agents must be ideally considered to avoid this serious disease.
Written by: Dr. Mai Foda