Mastitis Introduction & Immunity Flashcards
Define mastitis
Inflammation of the mammary gland
Describe the features of subclinical mastitis
Infection present
No viable clinical signs
Changes in SCC, milk quality and milk yield
Describe the features of clinical mastitis
Visible changes in udder, milk and cow
Describe the different grades of clinical mastitis
1 = mild changes in milk
2A = acute, changes in milk, udder hot and painful
2C = chronic, changes in milk, udder hard and lumpy
3 = changes in milk and udder, cow is sick
How do cows get mastitis?
- Viable pathogens on the teat end
- Bypass the sphincter and streak canal
- Spread into the udder
Name 3 environmental mastitis pathogens
E.coli
Streptococcus uberis
Klebsiella spp
Name 6 contagious mastitis pathogens
Streptococcus uberis
Streptococcus agalactiae
Streptococcus dysgalactiae
Staphylococcus aureus
Coagulase negative staphs
Mycoplasma spp
Are contagious organisms gram +ve or -ve
+ve
Are environmental organisms gram +ve or -ve
Gram -ve
What must happen for an infection to establish in the gland - considering that the mammary gland is constantly exposed to infectious agents from her environment and from other infected cows
For an infection to establish in the gland the bacteria must gain access through the teat canal, multiply at a rate sufficient to prevent its elimination or adhere to host tissue
Where do contagious organisms live?
On or in the infected animal
What are the consequences of mastitis infection in the cow?
- Clear the infection: immune system acts before signs develop, likely more mild so the infection clears itself
- Not clear the infection: chronic infection -> spreads within the herd. permanent damage to the udder, reduced milk yield. Death due to toxaemia
What do the consequences of the mastitis infection to the cow depend on?
Number and type of invading pathogen
Cow’s immunity
How does mastitis affect milk?
Higher SCC
Decreased storage time
At what SCC does milk become unsellable?
Milk that is repeatedly over 400,000 cells/ml in the bulk tank is unsellable – legal limit – averaged over a period of time
Describe mastitis as a herd problem and the role of vets
- Rare for Vets to treat individual cases unless systemically ill (Grade 3)
- Outbreaks CM or SCC
- Sick cows
- Raised bulk tank somatic cell counts or bactoscan
- Advising and Prescribing Lactating Cow and Dry cow Therapies
- PREVENTION STRATEGIES
Describe the mammary gland defence system
- innate immune system
- Fire line of defence
- Activates the acquired immune system - Acquired immune system
- Humoral and cellular memory
The innate immune system is comprised of..?
Resident leukocytes
Antimicrobial substance in milk
Act in the teat canal and teat skin
What is the major source of insult/injury to the teat skin and teat canal?
Milking machine
What is the aim of the mammary gland defence system in terms of the teat skin
Prevent colonisation of teat skin with bacteria
- Stratified squamous epithelium plus bacteriostatic fatty acids
What are the challenges of the defence system in terms of the teat skin?
- Some skin bacteria are ubiquitous
- Compromised by bruising, chapping, trauma (calf sucking, abrasion, etc), teat lesions (e.g. warts).
- Deals with milking machine
Which parts of the milking machine can damage the teat skin?
Vacuum (vessels)
Pulsation (massage/force)
Liners (friction)
Over milking
How can damage to the test skin be redcued?
Post milking teat dips emollients
Prompt treatment teat lesions
Good milking machine function
Which mastitis bacteria are ubiquitously present on the teat skin?
Staph aureus, Strep dysgalactiae
When can bacteria enter the teat canal?
When the teat canal opens during and after milking
What acts as a barrier of the teat canal?
Teat sphincter - but this takes 20-30mins to close after milking
What seals the teat when the cow is dried off?
Keratin plug
What acts as the primary physical barrier to the invasion of mastitis pathogens in the udder
Teat canal
What are the causes of teat canal damage?
- Milking machines: Hyperkeratosis (soles of your feet!)
- External trauma to teats
- Teat lesions
- Teat cannula
What are the causes of teat end hyperkeratosis?
Excessive milking vacuums
Faulty pulsations
Liner types
Teat shape
Rough or very rough
Increased risk of mastitis
How can the teat end and canal be proetcted?
Genetics
Milking machine
Loafing time post milking
Teat sealants at drying off
Describe loafing time post milking - when you would and wouldn’t want to use it
- Cows shouldn’t be able to lie down for 30 mins post milking to allow time for teat canal to close
- Need to be given something to do i.e. eat
- BUT if there is a lameness problem in the herd this can make it worse – need to weigh up risks/concerns
Which resident leukocytes contribute to a cows SCC?
Mainly macrophages, neutrophils, T lymphocytes
What is the role of macrophages, neutrophils, T lymphocytes in the udder?
Trigger the acquired immune system by release of pro-inflammatory mediators and antigen presentation
List the 4 antimicrobial substances in milk
Lactoferrin
Lactoperoxidase
Lysozyme
Free complement
What is the role of lactoferrin in milk
Iron chelating protein produced by epithelial cells and leucocytes.
Highest concentrations in the dry period and inhibits growth of bugs requiring iron e.g E.Coli
Describe the role of lactoperoxidase in milk
Bacteriostatic agent
Describe the role of lysozyme in milk
Bacteriocidal agent
Describe the role of free complement in milk
Produced by hepatocytes - aid in opsonisation of bacteria, activated it attracts phagocytes
Which components of the immune system are used in the acquired immune system
- Invasion of circulating neutrophils
- IgG2 antibodies
- B and T lymphocytes
- Inflammatory cytokines
What is the function of neutrophils in the acquired immune response?
Most important cell in the acquired immune system
- In response to release of pro-inflammatory cytokines, neutrophils adhere to and migrate along the endothelial cell surface towards the site of infection
- Then migrate through the tissue to the site of infection and destroy bacteria by phagocytosis
Which other component of the acquired immune system aids neutrophils in destroying bacteria by phagocytosis?
This process is aided by the presence of opsonising antibodies coating the bacteria
Why are large numbers of neutrophils required in the udder compared to other tissues?
Because of the dilution effect in milk and their reduced capacity to function in milk
Describe the roles of B lymphocytes in the acquired immune system
- Circulate through lymphatic system where they are exposed to antigens in tissue fluids
- Initial response produce IgM, IgG1
- Repeated exposure produce IgG2 antibodies (“vaccination”)
- IgG2 antibodies then circulate and enter inflamed udder aiding opsonisation of pathogens by neutrophils
- Present antigen to T lymphocytes
Describe the roles of T lymphocytes in the acquired immune system
T helper cells - production of cytokines following antigen recognition stimulates immune response
T cytotoxic cells – eliminate host cells invaded by pathogens
Describe the roles of the 4 different antibodies in the acquired immune system
- IgG2 most important antibody response
- IgM fixates complement for opsonisation of pathogens, agglutinates bacteria, neutralizes toxin
- IgA agglutination of bacteria and neutralize toxins
- IgG1 opsonisation of bacteria
How are genetics involved as a factor affecting mammary gland immunity?
Complex trait, low heritability:
- Udder types, Speed of Milking, Increased yield,
- Neutrophil function, Major Histocompatibility Complex
Between breeds variation: Brown Swiss, Montbeliarde lower SCC and clinical mastitis frequency than Holstein
Within breed variation
Genetics can be used to select for which 3 factors?
1) Low somatic cell count, using SCC as an indicator of mastitis
2) Udder conformation
3) Yield
What is the concern of SCCs being too low?
Lowered resident leucocytes -> increased susceptibility to mastitis
How does the stage of lactation act as a factor affecting mammary gland immunity?
- The stage of lactation has a key effect on the outcome of infection
- Dry Period and Early Lactation
- During the dry period many new bacterial mastitis infections are acquired and existing bacterial infections persist despite the use of long acting antibiotics at drying off
At which stages of lactation are cows at high risk of acquiring new infections?
Early dry period
Late dry period (peri-parturient)
- Although pathogens invade at this stage clinical disease usually seen in first 6 weeks after calving
Describe why infections are more likely in the dry period?
- Cessation of milking -> increased intra-mammary pressure & widening of teat canal
- Bacteria not flushed out
- No teat dipping
- Keratin plug….only 50% of cows have adequate seal by 10 days post dry off
- WBC function reduced
Why is WBC function reduced in the early dry period?
Neutrophils present in high numbers in secretions but full of fat and cellular debris so function impaired
Why is WBC function reduced in the peri-parturient cow?
- Increasing levels of IgG1 for colostrogenesis may interfere with neutrophil capacity to deal with pathogens
- Neutrophil recruitment and phagocytic ability is reduced
- High levels of cortisol, oestradiol and progesterone? Nutrition?
- Macrophages also have reduced phagocytic function
How does nutrition acts as a factor affecting mammary gland immunity
Negative Energy Balance
Vit. E and Selenium levels
Sub-acute Rumen Acidosis SARA
Hypocalcaemia
Why is a negative energy balance a risk factor?
Leucocytes from cows in NEB impaired activity, lower number
Why are vitamin E and selenium levels a risk factor?
Optimum (1000iu and 4mg)
Deficiency results in slow migration and weaker activity of leucocytes
How is SARA a risk factor?
Reduced appetite -> reduced DMI -> NEB
Diarrhoea -> poor cow hygiene
How is hypocalcaemia a risk factor?
Weaken teat sphincter mechanism
Can mastitis be vaccinated against?
UK only one vaccine (Startvac)
- Protects against Staphylococcus aureus, coliforms and coagulase-negative staphylococci
- Reduce incidence of sub-clinical mastitis
- Reduces incidence and severity of the clinical mastitis
