Autumn Lamb Mortality

Pasteurellosis

November is traditionally the peak month for systemic pasteurellosis due to Bibersteinia trehalosi but we have already seen multiple cases. Pasteurellosis due to Mannheimia haemolytica has also been diagnosed. If several lambs are found dead, it is useful to submit two or more as the findings are often more typical in one.

• The risk factors for systemic pasteurellosis are well known but often unavoidable e.g. handling, mixing, transportation, a recent move to better grazing/brassicas, or introduction of concentrates.
• In most cases the lambs had received a full course of pasteurella vaccine.
• The exposure of naïve lambs to tick borne fever can predispose to pasteurellosis but is only likely to apply in a minority of cases e.g. purchased lambs introduced to ticky ground for the first time.
• We don’t often consider border disease when investigating disease outbreaks in sheep. History would again be key e.g. mixing of lambs purchased from multiple sources.
• In contrast, concurrent high worm burdens +/- selenium or cobalt deficiency are common findings and will be contributing to losses.

Parasitic gastroenteritis

In a repeat of last autumn, we are also recording lamb deaths due to PGE.

Liver fluke

None of the lambs examined so far this autumn have any evidence of liver damage due to Fasciola hepatica. 

Considerations to prevent future deaths:

• Monitor worm egg counts – without delay if last treated 4 or more weeks ago, and irrespective of whichever anthelmintic was used.
• Repeat worm egg counts every 4 weeks.
• Check trace element status – particularly cobalt and selenium.
• Monitor for evidence of liver fluke infection – if bleeding for trace elements the Fasciola hepatica antibody ELISA can be added.
• Consider a pasteurella only booster vaccination.

Posted by SRUC on 03/11/2026