“I brought the hoggets home yesterday and they were really coughing all the way down the track to the yards. Some were panting and coughing once they were yarded, it wasn’t hot, so why would they be doing this and should I be worried about it?”
Sheep cough, particularly with exercise, if they have pneumonia and pleurisy. They can also cough if they have a burden of lungworm, or if you have just given them an oral drench and some have swallowed it down the wrong way. This in turn will cause inhalation pneumonia.
Pneumonia and pleurisy is caused by a mixture of viruses, bacteria and environmental conditions. If you muster and yard sheep in hot dusty weather they will open mouth breathe and take in dust and dirt to their lungs. This irritates the lining of the airway tubes and allows bacteria that normally just live in the airways to grow in the membranes and cause infections. Viruses will do the same thing, yarding and shedding gives shared airspace with inhalation of other sheep breaths. This allows viruses to spread from one sheep to the next (think COVID 19), then the mild infection they cause again allows a secondary bacterial infection to develop. Pneumonia and pleurisy is often asymptomatic in the grazing animal, but with exercise coughing starts. The kill sheets will show you that the disease is present, and these animals will have lifelong effects in their lungs which slows their growth rates. Avoiding movement and yarding during hot times of day, minimizing yarding and shedding events, having pastures without endophytes that cause heat stress will all help to reduce the incidence of this disease.
Another cause of coughing is lung worm, or verminous pneumonia. Dictyocaulus filariae is the sheep lungworm. The larvae are ingested from pasture and pass from the gut via the blood stream to the lungs where they develop into adult worms in the bronchi and bronchioles. This causes coughing and the worm eggs pass from the back of the throat into the gut, then out onto pasture. The good news is that most worm drenches will kill lungworm. Ask your vet which one they recommend.