Research continues into respiratory illness in sheep

LARYNGEAL chondritis in sheep is an upper respiratory tract disease most commonly found in Texel and Beltex sheep and their crosses. It has recently been researched by vet Ben Strugnell and Dr Katie Waine of Nottingham University, who still have many questions that remain unanswered. They hope that further investigation will help to reduce the number of cases.

Laryngeal chondritis (LC) was identified as the most frequent cause of death among 170 tups that were subjected to a post-mortem over a five-year period. It causes breathing difficulties and is potentially fatal.

“LC was responsible for some 17 per cent of deaths in tups of all breeds and a high percentage of cases were Texel or Beltex. It also occurs in a small, but significant, proportion of Texel and Beltex ewes and fat lambs,” said Mr Strugnell who runs Farm Post Mortems, near Barnard Castle.

“Its prevalence among these breeds has led to it being termed ‘Texel throat’, with the main outward symptoms being breathing problems, and/or noisy breathing. The Texel Sheep Society has strongly supported research into the disease and many of its members are keen for more progress to be made.”

Preliminary findings have shown that the larynx of the affected sheep is funnel-shaped and the vocal folds are touching when the animal breathes or bleats. This physical difference is believed to be the starting point for the condition. By comparison, the larynges of the Blue-faced Leicester animals that were studied were cone-shaped and the vocal chords were not touching. This finding was established following post mortem examinations of 23 examples of larynges from each breed.

“It is believed that in sheep that are predisposed to LC, the coming together of the vocal folds causes physical damage over time. In turn, the resulting mucosal lesions render the tissue vulnerable to infection by bacteria, which are probably already present under natural circumstances. The infection causes inflammation in the throat, with the swelling eventually blocking the airway and causing death by asphyxia.”

It is likely that there are elements of pathology in Texel and Beltex larynges, which do not cause death, he stressed. The reasons why the diseases progresses in some individuals are not fully understood.

“Anecdotal evidence suggests that affected tups tend to die as lambs or shearlings – if they make it through the first breeding season they will usually survive. I am reluctant to make definitive statements as there is a lack of certified research on LC, but it seems to be more prevalent in males.

“It has been suggested that there could be a hormonal connection or it might be exacerbated by the extra strain on the larynges as noise levels and exertion increase at tupping time. The warm weather can make the condition worse, as the animal will breathe more heavily in high temperatures.”

Focusing on the causes of LC has led Mr Strugnell to speculate whether the breathing issues have an effect on other parts of the body. He pointed out that respiratory distress is known to place strain on the connective tissue, leading to a ruptured diaphragm and even aneurism (burst artery), in some cases. Therefore, a chest or muscular abnormality may be a factor.

It is not possible to be specific about the incidence of LC in the national sheep flock at present, he said. In future, similarities might be found between LC and the brachycephalic dog breeds like the pug, which are short-nosed and flat-faced.

“The physical characteristics of the Texel and the Beltex, with their short nose and neck and stocky build, could be a predictor. My work with Dr Waine to measure traits like neck circumference and its relation to LC has so far produced no conclusive results.

"However, study numbers have been low due to a lack of funding. If LC is a conformational problem there could be a genetic component, but it is almost certainly not caused by a single gene.”

He is hoping to collaborate with Scotland’s Rural College to find answers.

Mr Strugnell said: “One idea is to incorporate the relevant measurements into the data-set at the same time as CT (computerised tomography) scans are being taken of rams. In the meantime, it makes sense to avoid breeding from any sires that have exhibited shortness of breath, even if their confirmation makes them highly attractive otherwise as a breeding prospect.

“LC is a health and welfare issue within the national flock, as well as having an economic impact on the farm business. It is important that we make efforts towards a greater understanding of the disease, so that we can take logical steps to reduce its incidence.

“At this stage, the research has only provided a starting point for an investigation into how breeding and selection programmes might be implemented to combat the problem.”