Illthrift In Ewes – A Short Summary

This blog by Dr. Ben Walker, a new graduate farm vet in the north of England, discusses the common issue of "illthrift" in ewes. Illthrift refers to a condition in sheep where they have a normal appetite but are in poor condition or experiencing weight loss, ultimately resulting in a failure to thrive. The blog explores high yield clinical facts to ace your exams!

Dr. Benjamin Walker is a new graduate farm vet working in the north of England. His key interests are in ruminant medicine, youngstock health and regenerative agriculture. Ben took a year out between college and studying at Nottingham vet school to travel to Australia where he worked on a 90,000-acre cattle station – mostly fixing fences and drinking beer!

Although sheep farmers are more routinely seeking veterinary advice with flock health planning it is still common to only visit some farms when things have already gone very wrong! One familiar presentation that might lead a farmer to seek advice is for ‘illthrift’ in their ewes. What is illthrift? Despite having a normal appetite, the sheep has poor condition or weight loss. Simply put it’s a failure to thrive! Poor condition reduces milk, meat and wool production and it can have financial and welfare implications. 

Questions about illthrift are frequently covered in vet school exams. The subject provides a means for examiners to test a student’s clinical reasoning and knowledge in a wide range of areas. Let’s break it down to work out how we can improve our understanding of this common presentation.

Recognising the problem

Farmers are most likely to pick up a problem with illthrift over the summer when lambs take longer to get to a target weight due to the dam providing a reduced amount of milk. Those paying close attention to data that can be collected on farm may also notice reduced scanning percentages (the ratio of lambs per ewe), a higher cull rate and reduced lamb birth weights, among other things. 

As with any presentation we need to carry out a clinical exam to build a clearer picture of the issue. It’s best to visit the farm and conduct a clinical exam on the affected ewes – those with poorest condition or the lowest body condition score (BCS). 

Building a differentials list

A differential diagnosis list is always valuable to help us get to the bottom of illthrift. Broadly speaking, illthrift in ewes can be divided into three main causes: nutrition, parasites and iceberg diseases.

  1. Nutrition – Obviously one area that needs to be investigated when looking at poor BCS is nutrition. We can subdivide this differential further:
    1. Energy / Protein – The ewes aren’t receiving enough bulk energy or protein in their diet to maintain condition. This can be investigated by looking at their diet.
    2. Minerals – Key mineral deficiencies that might cause illthrift include cobalt, selenium, and copper. Blood tests are the most effective means of checking that dietary levels are adequate.
    3. Dental disease – ‘Broken mouth’ is common in older ewes. Simply put, the ewes are unable to eat enough to maintain their condition and they need to be replaced.

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Figure 1: A broken mouthed ewe. Insufficient intake has led to drastic loss of condition.

  1. Parasites – Parasites are a common problem in sheep. In older animals this can be divided into liver fluke and parasitic gastroenteritis.
    1. Fasciola hepatica – Chronic liver fluke can cause problems in ewes because they cannot develop immunity to it. Tests include coproantigen ELISA, egg counts or abattoir reports.
    2. PGE – Monitor FEC to ensure that ewes are not facing an overly large parasite burden
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Figure 2: Bottle-jaw is a common clinical feature in ewes affected by chronic fluke (F.hepatica) or Barber’s pole worm (H. contortus). 

  1. Iceberg diseases – As the name suggests, finding an individual that is affected by one of these diseases is often just the tip of the iceberg. These diseases are hard to detect but can be very costly to producers. Each require their own tests and plans for control.
    1. Johne’s 
    2. OPA 
    3. CLA 
    4. Maedi-visna 
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Figure 3: Johne’s Disease .  ‌

Unlike Johne’s in cattle, Johne’s does not cause chronic diarrhoea in sheep. Instead, it presents as chronic wasting. As with other iceberg diseases it is challenging to find a firm diagnosis. Understanding the aetiology and diagnostic tests is important for vet school exams and for practicing vets! 

Tip: Draw a spider diagram or write flashcards for each of these common differentials and look for what tests and flock-wide control methods you would use – pay particular attention to the aetiology as this can help you understand the pattern of disease in the flock.

Remember – diseases don’t form orderly queues and flocks are frequently affected by multiple diseases at once!

Developing your understanding

Writing spider diagrams for common presentations is a great way of preparing for finals. They can help you fine tune your clinical understanding, refine the questions you would ask as part of a history and help you understand why you carry out certain parts of the clinical exam. Another vital part of developing your understanding is by testing yourself! VetTutor has a question bank including lots of farm questions to help test your understanding and providing resources for you to fill the gaps!

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