Disease diagnostic data from the last five years highlights a spike in the number of lambs succumbing to pasteurellosis during September, October and November.
Dr Katie Waine, of the University of Nottingham, says last autumn pasteurellosis – the pneumonic and septicaemic form – was the most common cause of death in lambs.
Dr Waine says: “As part of this project, I collate information from Farm Post Mortems on diseases that have been seen over the previous three months and produce quarterly reports.
“We also talk to farmers who have submitted dead stock and their vets to try and establish why losses have occurred.”
She says this farmer feedback suggests the main reason so many lambs succumb to pasteurellosis in autumn is simply because they have not been vaccinated against the disease; or sometimes animals have only received the first dose of vaccine and not the second dose four to six weeks later which is necessary to prime effective immunity.
“Incomplete vaccination and sometimes no cover at all are often why lambs typically succumb to this devastating disease.
“Quite often, dead lambs we see in autumn also have high worm burdens or trace element deficiencies, which could have contributed to the pasteurellosis.”
According to vet Ben Strugnell, of Farm Post Mortems, pasteurellosis is an opportunistic disease that can be triggered by many factors, such as worm burdens, change of diet, border disease, trace element deficiency, adverse weather or overstocking.
He says: “Autumn has always been a significant risk period for this disease because of the abundance of these different triggers during this time. We certainly always see a peak of disease between September and December every year.
“The disease diagnostic data clearly shows this autumn peak of pasteurellosis is consistent and concerning and has important implications for effective control.
“It suggests that if producers are keeping store lambs during this period, they should talk to their vet or animal health provider about vaccinating them correctly.
“The key message is it is almost impossible to control the multiple, varied stress-related ‘trigger’ factors for pasteurellosis in lambs at this time of year, so the best advice to farmers is to make sure they have the best vaccination-induced immunity cover possible for the whole period they are on-farm.”
Mr Strugnell adds in many cases this will mean giving store lambs, which have had two vaccination doses earlier in their lives, a third booster dose in August/September, so they are fully immunised in advance of the autumn risk period.
He says: “Lambs which have already gone off fat, or which will be gone by then, do not need to be done. For those buying store lambs, it is advisable to try to establish that the incomers have had an initial vaccination course [two doses] and then give them a third one on arrival.
“However, this can often be difficult to determine. If an outbreak of pasteurellosis is encountered, it is important to assess the risk factors so disease can be prevented in the following year.
“This may involve blood sampling of lambs for trace element status and border disease antibodies, and/or egg counting for fluke and worms. Some assessment of dietary adequacy is also useful.”
Two types of pasteurellosis
■ In contrast to a healthy lung, which is spongy and full of air, a lung infected with this type of bacteria would be very dark red in colour, hard and compressed
■ The natural reaction of the animal’s immune system in this situation is to try and get rid of the infection, which ends up being a vicious cycle of bacteria damaging the lung and the body’s defences working against it, which leads to further inflammation and damage
■ In some instances, this process can produce a fluid which causes lungs to stick to each other and means the lung is not able to expand to get the air in it needs
■ Eventually, the lung tissue becomes unable to take oxygen in, which it would normally transport around the body
■ This is the point where animals will display visible symptoms, such as breathing more quickly and heavily, as they struggle to get enough oxygen in to transport around the body
■ This occurs when bacteria get into the bloodstream and it often explains sudden death in store lambs
■ It works very quickly, which is why animals can appear to be healthy one evening and dead the following morning
■ Although these sudden death cases do not always display a lot to see at post-mortem, infected animals can display a damaged oesophagus with multiple ulcers on the inside surface, rather than a smooth pipe connecting the mouth with the stomach
■ Another classic sign is bleeding under the skin, as bacteria in the bloodstream damage blood vessels and spread to the organs, leading to organ failure and death