Recent years’ Teagasc sheep conferences have tackled diseases which are relatively unknown among farmers, but growing in importance, and other ailments of great significance including ovine pulmonary adenocarcinoma (OPA/Jaagsiekte) and anthelmintic resistance.
Last week’s conference also highlighted a disease which many farmers may know little about called laryngeal chondritis.
The condition was discussed by Ben Strugnall, a UK vet who runs Farm Post Mortems Ltd in Durham, northeast England.
The practice was set up in response to a lack of post-mortem facilities in the region and Ben says it handles mainly sheep and cattle.
He says he has identified the presence of laryngeal chondritis in a significant number of rams submitted for post mortem in recent years and that this encouraged him to take a deeper look into the condition.
The condition was explained as being caused by damage and inflammation and a bacterial infection in the arytenoid region of the animal’s larynx with the condition present in various levels of severity. It was suggested that the infection might occur due to traumatic damage to the laryngeal epithelium resulting from vocal cords clashing or increased airflow speed and turbulence leading to the surface becoming damaged.
There are numerous other veterinary terms used to describe its occurrence.
These can be broken down to the condition becoming established in a number of areas in the larynx leading to inflammation, swelling, abscessation/ulceration and necrosis (death of tissue) of the laryngeal cartilage and tissue.
This damage reduces the space available for airflow and restricts the animal’s ability to breathe with the most severe cases leading to mortality.
The Texel and Beltex breeds have been reported as having a predisposition to laryngeal chondritis. Ben carried out a study on 43 fallen stock aiming to examine the anatomical risk factors that could be responsible for the apparent increased risk.
He noted that the condition has been seen regularly in Texel rams submitted to him for post-mortem but also highlighted that Texels are by far the dominant breed type in the region and, as such, are likely to be over-represented in the sample size.
Leaving this aside, he carried out a comparison with the Bluefaced Leicester breed, which is the most common in the north of England, while another reason for selecting this breed is the significant anatomical differences between the two breeds.
This was aimed at putting the theory to the test that the disease was more pronounced in animals with a shorter neck and larger head size.
The study found that the shape of the Texel larynx and trachea was more funnel-shaped when compared to that of the Bluefaced Leicester and Ben surmised that it could lead to more turbulent airflow over the laryngeal epithelium.
There was a tendency for the vocal cords of the Texel rams examined to touch, which Ben said could restrict airflow further in sheep suffering from the condition.
He noted the presence of the condition to various degrees in Texel rams but the study could not link the presence of the disease in individual animals to any particular external anatomical features, eg neck length, height.
However, there were differences in the internal anatomy identified (the more funnel shape of the larynx).
He concluded by saying the condition is a very under-researched area and suggested areas for further examination.
These include measurements carried out in live sheep and a follow-up post-mortem examination to identify phenotypic traits that can be used to identify the disease and on a genetic basis to screen for the likely genes responsible.
Ben also raised the possibility of a link between laryngeal chondritis and a related syndrome of diaphragmatic rupture and aneurysm.
He hypothesised that the condition could be triggered by local anatomy and airflow forces applied as a result of laryngeal chondritis but, again, highlighted that further research is required in this area.
This aspect of the condition is not a typical feature in the cases seen in the Regional Veterinary Laboratories to date in Ireland.
Conference viewers were also informed of an Irish study involving the Irish Texel Sheep Society and industry stakeholders including the Department of Agriculture Regional Veterinary Laboratories (RVLs), University College Dublin School of Veterinary Medicine and Sheep Ireland with co-operation from Teagasc. A paper has recently been published in the Irish Veterinary Journal detailing the results of the initial aim of this study.
This included documenting flock health issues identified by members of the Irish Texel Sheep Society and to identify if laryngeal problems were perceived as an issue by Irish Texel farmers.
The results of the initial survey included responses from 65 breeders possessing both pedigree and commercial flocks with 60% of respondents having in excess of 50 pedigree ewes in their flock.
Respiratory disease was the most frequently identified flock health issue of those that responded, with some flock owners reporting multiple health issues on their farms.
Over 80% of these members surveyed indicated they had experienced some instances of “throat issues” with a maximum in-flock incidence of 10%.
The published paper highlighted caution with these estimates citing it was owner-reported data and that numerous factors could be responsible for these “throat issues”. Over 75% of breeders expressed a desire to be involved in future work.
The Irish Texel Sheep society said it is encouraged by the level of participation and support from breeders and that it is committed to exploring the incidence of laryngeal chondritis in the breed.
A spokesperson for the breed said: “Reports on the incidence of laryngeal issues vary greatly and there is a concern, as with any disease that there is relatively little known about, as to misdiagnosis and other health problems which display as respiratory issues being incorrectly attributed to laryngeal chondritis.
“We have yet to see conclusive evidence that laryngeal chondritis is exclusively associated with Texel sheep or that it is much more prevalent in the Texel breed. We know it is a condition that occurs in Texels and the society’s aim is to address this.”
Additional unpublished work was undertaken with the aim of identifying if laryngeal chondritis is identifiable in Texel sheep showing no signs of respiratory disease.
This was carried out through post-mortem analysis of animals that were asymptomatic for laryngeal chondritis.
While measurements have also been taken on larynges to identify if associations exist between these laryngeal measurements and laryngeal pathology. Speaking to the Irish Farmers Journal, the society said it has positive news to report with the investigating team confirming laryngeal ultrasound scans on live sheep show quality images that are being investigated to establish if scanned larynx measurements and laryngeal pathology scores correspond to changes found in post mortem.
“This is a positive step and further work is planned to investigate if it is possible by means of an ultrasound scan on a live animal to predict the susceptibility of that animal developing laryngeal chondritis symptoms. In the next phase of the study, it is planned to examine a number of clinical case animals with a view to correlating the ultrasonography findings with necropsy findings at post-mortem analysis,” the society said.
This part of the study was due to start in September 2020 but was delayed due to COVID-19 and the team at UCD is hopeful of getting this leg of the study up and running soon and has agreed a budget that will compensate the owner of the animal for forwarding clinical cases of laryngeal chondritis.
In the meantime, it is encouraging members to cull animals that show symptoms, refrain from breeding from these animals and to submit fallen animals for post mortem.
It has also worked closely with Sheep Ireland in the development of a facility where breeders can record incidences of laryngeal chondritis while the condition is also one of the traits now recorded in Sheep Ireland LambPlus flock visits.
The Texel Society concludes: “It is ultimately the aim, through further investigative work that will involve live scan measurements, post-mortem analysis and LambPlus records of animals with laryngeal chondritis symptoms, to investigate if there is a genetic link and if a breeding value for laryngeal chondritis can be developed.”