Cattle herd health Flashcards
Epidemic vs endemic
Endemic = found in almost all populations of cattle
Epidemic = will cause disease regardless of husbandry because the population is naive
What are negative and positive predictive values dependent on
The test
and the population to which the test is applied
What age do we need to wait for youngstock to reach to do ELISA serum test for BVDV and how many do we need to test
Wait until 9 months for maternal antibodies to clear
Need 5 samples; as would expect high seroprevlance if there was a PI in the herd
What disease is assocaited primarily with immunosuppression and reduced fertility
Bovine viral diarrhoea virus
What false +ves can multivalent pneumonia vaccine give
IBR
Bovine viral diarrhoea virus
How does the IBR marker vaccine work
Deletion of the glycoprotein E; can still seroconvert to wild type if they get infected but won’t get latent infection
So can use serology with gE +ve/-ve to say whether natural infection or vaccination has caused IBR +ve
What causes Johne’s disease and which animals get it
Mycobacterium avium subsp paratuberculosis
- Animals get infected early in life but don’t present until age 5-7
Is faecal culture a good test for Johne’s
No
It takes weeks to get back and due to intermittent shedding get lots of false negatives
Are serological tests for JOhne’s good
Not really - low sensitivity so lots of false -ves
But very high specificity so any that test +ve definately have it
How might a recent TB test affect a Johne’s test
There is some cross-reactivity
Some argue exposure to this mycobacterium avium protein will sensitise the body if infected with Johne’s so will increase sensitivity of the test (but do lose specificity due to cross reaction_
Why is Johne’s serological sensitivity so low
Because animal doesn’t produe antibodies until a long time after first infected
NB: can get spikes of antibody at times of stress e.g parturition
Can use repeat testing to increase the sensitivity
What test can we use to confirm Johne’s infection if get a +ve on serology
Faecal PCR
How often is Johne’s testing done in dairy vs beed herds
Dairy: individual cow milk serology done quarterly
Beeg: individual blood serology annually
(this is with accrediation )
What does a best linear unbiased estimate tell use
What percentage of performance is due to pedigree rather than environment
i.e looks at pedigree info, family performance
What is the breeders equation (looking at response to selection)
Response to selection (S) = heritability^2 x selection pressure
