Salmonella spp. are enteroinvasive gram-negative bacteria - all known species / subspecies are pathogenic and a significant cause of acute and chronic diarrhoea and death in various domestic and wild species. Salmonella enterica subspecies enterica serovar Orion (hereafter referred to as Salmonella orion) was isolated from this case. The main strains of Salmonella in calves are S. typhimurium and S. dublin. In calves, disease can present as acute septicaemia and / or enteritis, through to more chronic enteritis. The more severe disease presentations are usually seen in young animals. Many calves carry salmonellae within the gut, but disease does not develop unless there are other predisposing factors. These include: inadequate colostrum intake (failure of passive transfer), poor feeding hygiene, environmental stress, overcrowding and mixing of different ages. Recovered animals may become chronic carriers or develop polyarthritis or necrosis of the ears and tail tips
Sporadic sudden death in very young calves has been occurring at a dairy since December 2017 with a range of symptoms. Deaths have occurred in calves as young as 24 hours, or up to 3 days old, some have had symptoms of diarrhoea, others not. In total 10 or 12 calves from 40-50 have been found dead early in the morning over the past 4 months.
The dairy is a considerable distance from the consulting veterinarian’s practice, and the vet requested that PIRSA assist in a diagnosis.
The dairy is a large modern operation that is well managed and calves have a routine of removal from mothers at 12 hours after birth, given a drench of (tested) colostrum, then chained in individual shelters or hutches designed for the purpose until they are 4 weeks old, when they are moved into batched accommodation.
Sexed semen is used and calves are deemed to be high genetic merit. Deaths in calves of any age have been rare on the property until this time. The concern in this case has been the very young age of calves dying, often without any apparent signs of illness.
One or two calves at a time have been found dead early in the morning, in some cases without any apparent signs of illness. Deaths have occurred in an irregular pattern with sometimes weeks passing with no deaths.
I was contacted on 5th April to assist in the investigation and I was again contacted regarding further sudden deaths, the last being 2 calves on 18th April. A previous difficulty has been the problem of doing examinations in a timely manner, particularly over summer months, so the owner was encouraged to report further cases early so that autopsies and examinations could be done.
The first calf examined on 5th April was a large bull calf found dead in the morning. The calf had been 3 feeds normally, and was healthy in the evening. There were no obvious external or internal injuries or pathology noted, and the body appeared to be in good condition and not dehydrated. The weather has been mild and the accommodation good. A limited number of samples were collected, including brain but no significant findings were made from histopathology in this case.
Two more calves found dead on 18/4/18 were examined. One calf was 24 hrs old, and the other 3 days old, both were of average size and the bodies appeared dehydrated, with evidence of mild scours. Another calf in the rearing area appeared unwell, with a slight scour but body temperature was normal, although slightly dehydrated. This calf had been treated with antibiotics and an anti-inflammatory compound. I observed a large number of flies around the heads of some calves, but few flies in the nearby dairy area and there were some scours on the ground in the rearing area.
PM changes were similar in both calves with congested, purple coloured small intestines, and enlarged mesenteric lymph nodes. On the cut surface the affected intestines were haemorrhagic and one calf had multiple petechial haemorrhages in the stomach wall. Both brains appeared to have congested or inflamed meninges, and one calf had mild congestion of the lungs - possible PM artefact. The changes had the appearance of a per acute septicaemia.
The necroinflammatory lesions and severe congestion seen within the small intestine of these two young calves is compatible with acute bacterial enteritis, most likely enteric salmonellosis.
Salmonella spp. was isolated from the fresh intestinal samples submitted for both calves. One of the calves also had E. coli K99 antigen detected in intestinal content, but the intestinal changes are too severe to be attributed to enterotoxigenic E. coli.
The draining mesenteric lymph nodes exhibit acute fibrinosuppurative lymphadenitis, with plugging of afferent lymphatic vessels by fibrin thrombi containing degenerate neutrophils. This reflects drainage of inflammation and bacteria/toxins from the inflamed gut.
The meninges are markedly congested and oedematous, but there is no evidence of inflammatory cell infiltration to indicate meningitis.
There are very few described or observed causes of sudden death in calves younger than 3 or 4 days old. Some of these are listed below in order of likelihood.
In this case deaths have been sporadic, with no identifiable stressor or cluster of factors. Calves are routinely fed (tested high quality) colostrum, when taken from cows 12 hours post calving and accommodation is individual hutches that provides good shelter and separation. Most dead calves had some evidence of scouring prior to death, but deaths are peracute, often overnight in calves that appeared relatively normal the evening before.
On the day of the 2 calf PMs I noticed a lot of flies infesting the calf area & clustered on the noses of recently fed calves - this is a possible route for transmission of an infective agent, and it may be possible to apply lime around areas contaminated with scoured faeces and apply fly treatments around the hutches as well. Faecal contamination of the calving area is another possible route of exposure, and advice about management of this area has been provided to the owner by the consulting Veterinarian. The use of a Salmonella vaccine in calving cows has also been discussed.