Sudden death in young sheep is rare in pastoral areas of SA, and may occur due to a range of conditions. Unusually wet spring and summer conditions appear to bring unusual conditions with them. While vaccination against clostridial diseases and worming sheep can prevent a number of common causes, occasionally deaths still occur for which a diagnosis can be difficult.
In northern regions of South Australia summer temperatures can be high, and during harvest sheep may not be observed as frequently as usual and this can lead to mortalities that may not be detected for a few days. In this climate it can be difficult to get good quality PM samples from a sheep that has been dead for more than a few hours.
Fortunately ocular fluid, brain and rumen observations can still be helpful in some of these cases, even when other tissues and organs are autolyzed. In this case acidosis was diagnosed in an autolysed lamb carcase.
Grain harvests in the North of SA were at record levels this summer, and have been delayed by wet weather, so there has been a higher than normal amount of grain heads remaining in stubble paddocks.
On this property there have been an unusual number of sporadic deaths in lambs over the past 2 months, approximately 30 lambs had died. The season has had an unusually cool and wet spring and summer, and lambs are born in August/ September. An investigation of 1 dead lamb approximately 1 month previously by the local vet was not diagnostic and the property is well managed and sheep in good body condition with a good vaccination and worming program, suitable to normal conditions. Two lambs were found dead this morning and one was available for PM at approximately 1pm. Some scouring in the lambs has been observed in this mob. Lambs have been grazing a freshly harvested stubble paddock, and good quality water is available.
On post-mortem examination the 5 month old lamb was autolyzed so very limited samples were collected including brain, ocular fluid (aqueous humor) , fluid intestinal contents and a sample of abomasum. The temperature was around 41C that day. The lamb appeared to have been in good condition. A urine dip stick indicated pH of rumen contents were 5 or below and there was an usually high proportion of wheat grains visible.
A smear of intestinal contents revealed Cryptosporidia spp with no parasite eggs with a small number of coccidia.
However, D-lactate from aqueous humor was 9.4 mmol/L (0.0 – 0.5) indicating ante mortem acidosis.
The degenerative histological changes observed throughout the brain sections are most likely attributable to post-mortem autolysis +/- formalin fixation. There is no convincing evidence of inflammatory CNS disease, polioencephalomalacia or focal symmetrical encephalomalacia (clostridial enterotoxaemia).
The abomasal sections also exhibit moderate mucosal autolysis; however, there is suggestion of mucous cell hyperplasia and metaplasia, as typically seen in response to gastrointestinal parasitism (e.g. Teladorsagia spp. Interestingly, the faecal egg counts (bulk sample submitted and caecal content from this animal) were minimal, which may suggest some other cause of mortality in this animal.
The caecal content was positive for Cryptosporidia on smear. Cryptosporidiosis (C. parvum) is primarily an enteric disease of lambs less than 30 days of age and usually causes mild scouring. Significance of this finding in an older lamb is uncertain.
This lamb may not be representative of all the lambs dying on the property but does indicate that even an autolyzed carcase can provide helpful information in some cases. In this case both the necropsy findings of grain in the rumen and a rumen pH of 5.0 indicate ruminal acidosis. The elevated aqueous humor D-lactate levels confirm the diagnosis.
Other deaths in the flock could be from internal parasites or other issues. Cryptosporidia is unlikely to be a sole cause of deaths in the flock, but may be contributing, as could coccidia in some cases. The producer wormed the lambs again and treated them with sulphadimidine (for coccidiosis) and noted a gradual improvement in condition.
It would be helpful to monitor faecal egg counts in particularly the lamb flock in unusually wet seasons, and the group should be observed carefully when introduced to a paddock where there may be available grain after harvesting.