A pilot study to investigate diseases present in cull ewes by examination of viscera retrieved at slaughter

Project number:                    61110019

Lead contractor:                   Farm Post Mortems

Start and end date:              01 October 2015 – 31 October 2016  

 

The Problem:

Ewe longevity is an important determinant of productivity on sheep farms. Involuntary premature culling of ewes represents a major cost as it directly impacts on replacement costs and causes indirect losses as a result of suboptimal performance of affected ewes. Cull ewes could be a source of useful information relating to the health status of the breeding flock, and could provide information on the causes of poor condition and premature culling. This information is generally at present not available to farmers because:

(a) cull ewes have low value and are often considered not worthy of veterinary investigation;

(b) cull ewes are often sold live and are difficult to trace to slaughter;

(c) carcase condemnation/ abattoir feedback data is not generally useful in investigating the causes of involuntary culling even when it is available

 

Aims and Objectives:

  • to establish a pilot scheme where producers can receive more disease information on cull ewes
  • to understand the reasons behind culling and collect detailed records and photos
  • to feed information back to producers and their vets to improve flock health status

 

Approach:

Cull ewes are submitted onto the scheme by producers and the appropriate organs are removed at slaughter.

The organs will be examined by a vet and detailed findings will be recorded.  A report will be produced and sent to the producer and their vet.

 

Results:

Sixteen flocks submitted ewes into the scheme with 111 ewes being examined. 73%. 13%, 6% and 19% of the flocks tested positive for Johnes, Maedi Visna, Ovine Pulmonary Adenocarcinoma (OPA) and lung abscessation. A positive status was assigned if at least one animal from the batch tested positive to any disease by any test.

Johnes disease was by far the commonest disease identified during this project.  This could be a serious finding for the industry. However, the fact that Johnes disease is present on a farm may or may not mean that it will be making a large contribution to farm efficiency and profitability, and that further investigations or interventions are necessarily justified. It is possible that on some farms, Johnes disease causes severe ill-thrift in a small number of individuals and there is scope for these to infect others is limited. Further work is much-needed to establish the significance of the infection on these farms.

Maedi Visna appears to be uncommon as a recognised clinical disease in the North East of England but seropositive ewes were found during this study.

Ovine Pulmonary Adenocarcinoma was only found in one flock (equates to 6% due to low number of flocks). A recent abattoir survey found the prevalence to be nearly 1%. This is surprising due to previous work on fallen stock which found a prevalence of nearly 6% in dead ewes. It could be that ewes with OPA tend to be found in dead ewes while the prevalence of Johnes may be higher in cull ewes.

Chronic Suppurative Pneumonia, or lung abscessation, has been identified in previous studies as one of the most important causes of death in adult ewes. It was interesting to find it in high prevalence on one farm in this study, and at a lower prevalence in another two. In the most severely affected farm, no other cause of ill thrift was identified, making this the main disease to focus on. There is much scope for better application of best practice with respect to needle hygiene throughout the industry.
In conclusion, this project has achieved its aim of proving the principle that:

1.    With some effort, ewes can be followed to slaughter and samples obtained from individual ewes to determine flock status for important production-limiting diseases
2.    The value of even quite ill-thrifty ewes can be offset against this testing, to reduce costs.
3.    This could provide a good initial screen especially for Johnes disease, which may be of interest to buyers of breeding females.
4.   Training vets already working at abattoirs to screen batches (on request) would make it very cost-effective
5.   There is an urgent need to evaluate the costs and impacts of intervention for the main production limiting diseases, especially Johnes Disease.