Mastitis in cattlw Flashcards
Which pathogens may cause mastitis via haematogenous spread
Brucella, TB
What are the most common pathogens causing mastitis
Staphs, streps, E coli
Which pathogens causing mastitis are most likely due to iatrogenic introduction
Cryptococcus and atypical mycobacterium
3 streps that most commonly cause mastitis
Strep dysgalactiae
Strep agalactiae
Strep uberis
Which bacteria is an OBLIGATE udder bacterium
Strep agalactiae
-> Means that infection usually permanent once acquired
Pathogenesis of strep agalactiae
Obligate bacteria of udder
- Not very invasive; get periods of flare ups with patchy penetration through epithelium then quiescence
Over time: repeated invasion/inflammation leads to fibrosis and involution
NB: mainly see this in older cows due to build up over time
Histology of strep agalactiae mastitis
Oedema and neutrophil infiltration
- Vacuolated epithelium with macrophages/fibroblasts
+ clinically udder is painful due to retained secretion
Key difference in histology between strep agalactiae and staph mastitis
Strep = mainly in duct space
Staph = mainly in tissue
Pathogenesis of staph mastitis
Usually catalase +ve and haemolytic staphs
> More damage to glandular tissue so MORE SEVERE
Common after parturition
> Get necrosis and gangrene of quarter; eventually sloughs
Can get toxaemia if peracute
More chronic form of staph mastitis pathogenesis
Organisms invade through epithelium and infect interstitium (go deeper than streps)
- Get foci of infection with granulamtous response and necrotic centre
–> These get walled off via fibrosis
Coliform mastitis pathogenesis
Infection relates to ENVIRONMENTAL EXPOSURE
> Often acute and can get septicaemia esp with E coli as more invasive
Inflammation centred on ducts
What type of mastitis do we see in farms that have eliminated classic forms
Coliform mastitis; more severe in these circumstances
Causative agent of summer mastitis
Trueperella pyogenes
Pathogenesis of summer mastitis
Affects non-lactating/immature glands
= Necrotising, suppurative condition in TEAT CANAL
Caused by T pyogenes; likely spread by flies
How does mycoplasma mastitis work
Sudden onset agalactiae
Udder is firm and hard but painless
Secretion looks normal BUT get separation when standing
What is different about infection route in mastitis from TB
Blood borne infection; haematogenous spread
Development of tuberculosis mastitis
= insidious
Progressive increase in size and firmness of gland
Milk appears normal for a long time
What does a cryptococcus mastitis gland look like
Firm, grey with haemorrhagic foci and shiny cut surface
Lots of liquefactive necrosis
What is the most common cause of mastitis
Streb uberis
Two broad classification of mastitis
Contagious: reservoir is on the animal
Environmental
5 point mastitis control plan
Regular milking machine maintenance
Post milking teat disinfection
Routine dry cow therapy
Prompt treatment of clinical cases
Culling cows with chronic mastitis
Grading mastitis 1-3
1: changes to secretion only
2: changes to both secretion and udder
(A = acute; C = chronic)
3: systemically ill cow with changes to secretino and udder
What does a water secretion vs clotted secretion suggest about nature of organism causing mastitis
Watery = coliform
Clots = gram +ve (streps and staphs)
Treatment approach towards gram +ve vs -ve mastitis
Gram +ve: more likely to cause persistent infection so want extended Ab course
Gram -ve: more likely to self resolve
How can we detect subclinical mastitis
Using somatic cell counts
California milk test: to work out which quarters are affected on a specific animal
What SCC levels do we consider to be infected or uninfected for individual cow
<200,000/ml = uninfected
>200,000/ml = infected
What is the legal SCC limit for bulk milk
400,000/ml
Minor factors affecting SCC counts in milk
Age, stage of lactation (low in middle), season, breed, milking fraction (first part is higher)
Why must we be careful about interpreting a single SCC reading as meaning subclinical mastitis
May be an already cleared TRANSIENT infection; SCC counts remain high for 1 month after clearance
How does California mastitis test work
Mix milk and detergent
- If there are neutrophils present, get broken down by the detergent which causes jelly mixture
- Graded: negative, trace, 1, 2 and 3
What is the legal limit on bactoscan detection of bacteria in milk
500,000
NB: often source of bacteria is from milking plant or teat contamination rather than from mastitis
Hygeine scoring cattle scale
1-4 where 1 is clean
How does milk letdown work in cows
Teats are stimulated –> oxytocin release –> stimulates letdown by myoepithelial cells contraction (NB: 80% milk is in alveoli and only 20% in milk cistern)
At what flow rates is risk of mastitis highest
Low flow rates
i.e start and end; END most important because don’t get large flushing flow of milk afterwards
Why do we need to do pre-stimulation of teats before milking
Because otherwise get biphasic milk flow
i.e flow from cisterna; then delay before let down
This causes LOW FLOW RATES
How long does it take most cows to milk out
5-7 mins
WHy is post milking disinfection important
Because streak canal stays open for an hour after milking
When should we expect teat orifice to be closed after milking finishes
20-30 mins
What causes hyperkeratosis of teat ends
Over milking or very slow milking
Increases mastitis risk because hard to clean
- Consider herd has issue if >20% teats rough or >10% are very rough
Clinical vs bacteriological cure for mastitis
Clinical = not eliminated BUT can sell milk
Bacteriological cure= have gotten rid of causative agent
In which mastitis type are we mainly targetting marenchyma (vs milk and ducts)
Staph aureus
In which mastitis type are we mainly targeting the cow systemically
Coliform
Which species are intramammary antibiotics useful for
Non-invasive ones
- Strep agalactiae and dysgalactiae
- coagulase -ve staphs (i.e NOT staph aureus)
In which organism mastitis are we likely to need pulse therapy to cure
Strep uberis
When do we want to use parenteral antibiotics as well as intramammary for mastitis
With grade 2 mastitis
> Deeper tissue of gland involved
> With invasive pathogens e.g staph aureus, strep uberis
When do we want to avoid using ocytocin as an adjunct to mastitis treatment
With painful mastitis
Because contraction of myoepithelial cells in painful
What should we reduce milk yields to before drying off
<15 litres
How long does involution take; from drying off
2-3 weeks
Why is there increased risk of infection at drying off
No flushing of bacteria teat with milk
Increased intramammary pressure can compromise the streak canl
What causes horseshoe shaped lesions on cow teat
Pseudocowpox = parapox virus
What is black spot
= necrotising infection of teat with fusobacterium necrophorum
