Clinical diagnosis in farm animals Flashcards
What history needs to be gathered for farm animals?
- Animal details: age, production stage, clinical signs
- Herd history
What are the on-farm assessments that need to be examined?
- Full clinical exam
- Sample for laboratory
- Exam if required
- Assess environment
- Housing and nutrition
Describe a ‘Blunderbuss’ approach to diagnosis
- Examine from top to toe
- Get every test carried out
- Fit the results to a textbook model or vets own database of disease
Why is a blunderbuss approach to diagnosis not an appropriate approach?
- Cumbersome
- Expensive
Describe an algorithmic approach to diagnosis
- Simple: will pick up common things but things can be missed
- Useful for training e.g. lay staff, farmers, SOPs but not good enough for a vet
- Inflexible
- “if this cow is recumbent and recently calved then she has Milk Fever”
- “if this cow has diarrhoea and is eating and is losing weight then she has Johne’s disease”
Describe a pattern matching approach to diagnosis
- relies on what you already know
- recognition of a pattern of signs e.g. Recumbent & Fresh calved & No quarter swelling = Milk Fever
Why is pattern matching not always an appropriate method?
- Can jump to conclusions without carrying out a full examination to look for all possible differentials
- Inflexible
- Don’t allow for intuition, experience or skill
Describe the hypotheticodeductive model as a method of diagnosis
- Generating and testing a hypothesis
- Source of the hypothesis based on: experience, history, patterns, physiology
A thin, bright, diarrhoeic cow could have?
Johne’s disease
What signs could allow a milk fever hypothesis to be generated?
- Experience: “older dairy cows who are recumbent after calving have milk fever”
- Physiology:
• Calcium is required for muscle function and gut function
• Ca is likely depleted after calving in the older dairy cow
• Recumbent cow post calving with absence of faeces is likely due to low blood Ca = Milk Fever
How can a milk fever hypothesis be tested?
- Take a blood sample and measure serum Ca
- Administer Ca Borogluconate i/v => Positive response suggests Milk Fever … and we’ve cured her
Describe probabilistic reasoning as a method of diagnosis
‘How we think’
“Interpret findings in the light of our previous knowledge”
- E.g. “sudden milk drop after calving”
- Differential list: Wire, Left displaced abdomen
- Examine cow: Anterior abdominal pain & decreased rumen movement & T 39.50C but EW negative. No “ping”
- Confirmatory test: WBC count
Define sensitivity and specificity
Sensitivity = proportion of true positives detected Specificity = proportion of true negatives detected
Define PPV and NPV
PPV = probability that a test positive is truly positive NPV = probability that a test negative is truly negative
Define prevalence
The probability that an animal has the disease
