Most shepherds will be familiar with the persistent coughs and dwindling growth rates of some weaned lambs in the autumn, store lambs in the weeks after arrival on farm or even ewes during housing. The majority of the time, these pneumonia cases are caused by the same offenders – Pasteurella bacteria species, such as Mannheimia haemolytica and Bibersteinia trehalosi. Last week, we managed to grow both of these bugs in the lungs of just one dead March-born lamb, from a group of lambs which had been struggling ever since weaning with poor growth rates, persistent coughs, and sudden deaths.

These bugs live in small numbers in the tonsils of most sheep, though sometimes management and other disease factors can combine to weaken the immune system enough that they begin multiplying out of control, spread to the lungs causing pneumonia and sometimes even to the blood causing a rapidly fatal septicaemia. Management risk factors include stresses such as weaning, transport, marketing, handling, and exposure to inclement weather conditions. Housing at high stocking densities or in poorly ventilating sheds, especially if very damp, humid, or dusty, can also cause stress and poor air quality enough to induce disease.

Lambs struggling to fight off other diseases at the same time are also more susceptible to these on-board bugs. In the case mentioned above, the lambs were on very sheep-sick ground and were also fighting off significantly high worm burdens. Other health issues such as trace element deficiencies, other parasites and diseases also combine to increase the likelihood of disease occurring.

Back in the good old days of a reliable Heptavac/Ovivac P Plus supply, a lot of sheep were being covered for at least some of their productive life – however, we realised recently that the Pasteurella cover in this vaccine may only be protective for 3-6 months, meaning that farms having issues in the autumn are likely to need a booster dose 3-4 weeks before the risk period. Although we are still waiting for the return of clostridial disease cover, we can still get hold of Ovipast Plus, which will still cover sheep against the two main Pasteurella species when given twice, 4-6 weeks apart. Rather than stopping them “catching it” in the first place, it does give them some advanced cover ready for the stress-induced attempts by the bugs to multiply out of control and cause disease.

Please bear in mind that not all coughs and respiratory issues are caused by Pasteurella; Mycoplasma, MV, Jaagsiekte/OPA and even occasionally lungworm may also cause similar signs and should be investigated by your vets, especially if persisting in the face of recent vaccination.