Wasting Disease in Sheep: A Case Study for Vet Applicants

A farmer has brought a 3-year-old female mule ewe to the practice because she has been wasting away. The ewe has shown signs of lethargy and has had bouts of pneumonia throughout autumn. The farmer has noticed similar symptoms in other ewes and wants to get to the bottom of the issue. This is a common scenario that veterinary students and applicants may encounter during pre vet work experience. Understanding how to approach these types of cases is essential for vet school interviews.

Clinical Signs Reported by the Farmer

The farmer describes several clinical signs that need to be evaluated:

Wasting: What does the farmer mean by wasting? Is it muscle loss? Weight loss? Or both?
Pneumonia: What type of pneumonia is the farmer referring to? Is it characterized by nasal and ocular discharge, coughing, a raspy throat, or difficulty breathing?
Lethargy: Does the ewe seem lethargic? Is she separating herself from the flock or struggling to keep up? Is she failing to graze or stand?

These clinical signs point to a potential group problem rather than an individual issue, suggesting that multiple ewes in the flock could be affected.

Additional Information from the Farmer

Regular faecal egg counting & worm treatment: This implies that endoparasites, such as worms or liver fluke, are less likely to be the cause.
Heptivac P vaccination: This provides protection against clostridial diseases and pasturella pneumonia, suggesting that respiratory infections may not be the main cause.

Clinical Findings

BCS of 1.5/5: The ewe is much thinner than expected, as a healthy mule ewe should have a BCS of 2.5-3 in autumn. A low BCS suggests malnutrition or underlying illness.
Increased respiratory rate: This could indicate respiratory distress and requires further examination.
Abnormal respiratory auscultation: A crackling sound in the lungs suggests that the ewe may have pulmonary disease, such as Ovine Pulmonary Adenocarcinoma (OPA) or other respiratory issues.

Next Steps: Diagnostic Testing

The vet suggests performing a thoracic ultrasound scan to look for OPA (Ovine Pulmonary Adenocarcinoma). In this case, the ewe is confirmed to have OPA. Other possible causes of these symptoms include Maedi Visna, pleural abscess, and pulmonary caseous lymphadenitis.

Ethical Dilemma: The Wheelbarrow Test

The wheelbarrow test is a method sometimes used to diagnose OPA. In this test, the sheep's hind limbs are lifted, and if fluid (exudate) is seen coming from the nostrils, it indicates OPA. The fluid is a result of the tumors in the lungs producing exudate, which gives the lungs their crackling sound.

However, this test raises an ethical dilemma: Is it ethical to perform a test that may cause discomfort to the animal, especially if the result is already likely based on other symptoms and diagnostic testing?

EXAMPLE: Questions You Could Be Asked in a Vet School Interview

Questions you could be expected to answering during a vet school interview.

· Is this an ethical test to perform?

· What are the pros and cons of performing this test?

· What is your opinion?

Example of a answer

Is the wheelbarrow test an ethical test to perform?
- The ethics of the wheelbarrow test can be debated. While it provides a quick and direct diagnosis of OPA, it can cause distress to the ewe and may not always be necessary if other diagnostic methods, such as ultrasound, can confirm the diagnosis. The test could be considered unethical if it causes undue harm or discomfort to the animal when alternative, less invasive methods are available.
What are the pros and cons of performing the wheelbarrow test?
Pros:
- It is a fast and direct way to diagnose OPA, which can help in making immediate management decisions.
- It provides clarity for the farmer, enabling informed decisions about flock management.
Cons:
- It can cause unnecessary distress to the sheep, as it is invasive and uncomfortable.
- It may not be necessary if other diagnostic tests, such as ultrasound, can provide a more accurate diagnosis without causing stress.
- There is a potential for misdiagnosis or false results if the sheep does not show exudate despite having OPA.
What is your opinion?
In my opinion, I would lean towards using non-invasive diagnostic methods like ultrasound or laboratory tests first. These methods are more accurate, less stressful for the animal, and provide the necessary information to diagnose OPA without resorting to potentially painful or stressful procedures. The wheelbarrow test could be considered as a last resort if other diagnostic options are unavailable. Cost of diagnostics is an important factor to consider in this case; ultrasonography will be more expensive than the Wheelbarrow Test therefore may not viable in all farmers business models. It is important to acknowledge that farm animal medicine focuses on the health of the entire herd and short period of discomfort in a single individual with a long term benefit to the herd of the health may be preferable. In this case you may explore the use of culling and post mortem as a means of diagnosis as well.

Final Thoughts

This case study of wasting disease in sheep highlights several key diagnostic and ethical considerations that would be important in any pre vet work experience and vet school interview. Understanding animal welfare and being able to balance diagnostic accuracy with the ethical treatment of animals is critical in veterinary practice. If you're pursuing a career in veterinary medicine, reflecting on these ethical dilemmas and understanding the various diagnostic options will help you excel in your vet school interviews.