From a mob of 350 six month old cross bred lambs in an on-property feedlot, four lambs died suddenly on consecutive days. The final lamb was autopsied and the gross pathology initially appeared to be consistent with redgut. However more thorough exploration suggested that alternative intestinal accidents were the cause.
The lambs had been on feed for four weeks with no problems. Growth rates, general health and the alertness of mob had been excellent. There was no history of diarrhoea. The feedlot was inspected by walking through each morning.
The lambs were fed once daily, each morning in troughs. The ration consisted of 75% Barley and Wheat, 8% Mung Beans and 15% Barley Hay. Most of the barley hay was fed by placing a 480 kg rectangular bale in the yards every fourth day. Only 3% of the barley hay was in the mixall mixed trough ration. The lambs consumed the entire trough ration within a few hours, with the owner commenting how they ran to the trough and quickly fed.
Three mornings before the autopsy visit a lamb was found dead in the yards. For the three following mornings a dead lamb was found. The last of these was autopsied. Following the final death there have been no further problems with the mob eventually going to slaughter having achieved above average growth rates. It may be significant that following the autopsy management steps to reduce the gorging at the daily feed were recommended and introduced.
The feedlot is established in a set of sheep yards. This is the third group fed in these yards. There is no obvious source of arsenic but past usage (eg filled in dip, pump out site) cannot be ruled out.
The yard contains several white cedar (Melia azedarach) trees. The trees were at the time currently leafless and dropping berries. According to a number of sources these berries have been associated with a GIT poisoning syndrome. On previous feedings berries had not been present. In addition in the week prior to the visit the lambs had taken to stripping the bark from the white cedars. The lambs had also eaten bark from a pepper tree (Schinus areira).
The mob received two 5 in 1 injections around marking and a third on entry to the feedlot. The latter was in conjunction with injectable moxidectin.
The carcass had rigor mortis with no bleeding from orifices. Most of the GIT present in the abdomen was severely congested. This included the wall of the omentum, the wall of the rumen, the abomasal mucosa, the duodenum (which was intensely bloody with frank blood in the lumen) and the remainder of the SI.
At a point several centimetres cranial to the ileo-caecal valve the intense congestion faded to near normal. The colon appeared less affected and the small colon and rectum were normal. No torsion of the mesentery could be found. The spleen was enlarged and pulpy. Blood oozed from the cut surface. Urinalysis was positive for protein and glucose.
Samples were submitted to the NSW DPI Regional Veterinary Laboratory at Wollongbar. These found no evidence of bacterial enteritis, spleen smears were negative for anthrax and the histological changes were supportive of a gastrointestinal accident.
Redgut in sheep was initially reported in New Zealand with sheep grazing on lucerne (Gumbrell, 1997). It has also been associated with other pasture types and reported in other countries. It also occurs in calves, goats and a similar disease has been reported in pigs (Straw et al., 2002).
In sheep, lucerne and similar feeds are rapidly broken down into small particles that quickly pass through the rumenoreticulum, through the small intestine and onto the large intestine (Cruickshank et al., 1992). This leads to a decrease in the size of the rumenoreticulum and an increase in large intestine size. As a result of these relative changes in size, the large intestine can rotate clockwise up to 180 degrees. This can occur within 3 weeks of a different feeding regime (Jagusch et al., 1976 cited by Gumbrell, 1997).
It could be postulated that a similar situation may exist in these feedlot lambs, especially in any that are selecting not to eat the separately provided roughage and/or selecting the mung beans from the trough ration. This would result in a highly fermentable ration, which would spend little time in the rumenoreticulum, most likely leading to an increase in large intestinal size and a decrease in rumenoreticulum size. This tallies with Gumbrells theory (1970).
However the gross pathology of this case is not consistent with those usually reported for redgut. In this case there was a haemorrhagic appearance to the wall of the rumen, abomasum, duodenum and remainder of the small intestine (with the exception of the terminal ileum). In contrast, traditional redgut involves just the portion of the intestines supplied by the cranial mesenteric artery and vein, which is the small intestine that begins 100-120 cm distal to the pylorus (Gumbrell, 1997). The abomasum and duodenum are supplied by the gastric and gastroepiploic arteries and drained by the gastroduodenal veins. These are branches of the celiac artery.
So for this case to be subsequent to a torsion event, there must have been occlusion to both the gastric and gastroepiploic arteries (or celiac), as well as the cranial mesenteric, as the haemorrhagic areas of gastrointestinal tract involved from the abomasum to the terminal ileum.
Lesions that could look similar and cause sudden death are salmonellosis (culture negative) and enterotoxaemia (solid vaccination present) (Gumbrell 1997). In these cases it would have be interesting to have known the position of the intestines. In cases of redgut it is recommended to commence the autopsy with the animal on its back so that intestinal position can be assessed.
There are a number of alternative intestinal accidents that would explain the gross pathology seen at autopsy. The intestinal accidents seen in pigs are one possibility. Perhaps 6 month old feedlot lambs have some similar GIT elements to pigs, and as such the condition could be similar to haemorrhagic bowel syndrome or intestinal volvulus in pigs (Straw et al., 2002).
The gross pathology also has similarities to gastric-dilation volvulus (GDV) of deep chested dog breeds. Interestingly the daily gorging feeding of the lambs may have created a situation that has been proposed as being linked to haemorrhagic bowel syndrome in pigs.
"In pigs feeding disrupts the basic migrating myoeclectric complex pattern to varying extents, according to the volume of food ingested at one meal. The motor activity of the pig's antrum and intestine after one large meal resembles that seen in carnivores, and the duration of this effect is approximately halved when two meals a day are given. When pigs are fed ad lib, the motility pattern resembles that seen in ruminants, where the myoelectric complex pattern persists regardless of feeding, such as would occur if feeders became empty for a period of time, might be an inciting cause if gut stasis predisposes to HBS." (Ruckebusche and Bueno, 1976).
Another possibility is that of abomasal torsion. While no reports of abomasal torsion in lambs could be found in the literature, this condition does occur in calves. In young calves, right displaced abomasums (RDAs) are much more common than LDAs. RDAs can progress to torsion (RTAs). In an RDA the abomasum rotates dorsally up to 90-180 degrees. If this progresses to a RTA, vascular impairment occurs. If the omasum is also included the (OAT) the twist is usually at the reticulum. The dietary factors linked with LDAs, RDAs etc include low roughage, high concentrate diet and indigestion. These conditions could possibly exist in this feedlot operation as result of daily feeding and lamb feed selection.
While the absence of further cases prevented the exploration of the above possibilities, all are linked to dietary factors that were present as a result of diet formulation and feeding management. These include use of mung beans, separate feeding of roughage and once a day feeding that allowed rapid consumption of the daily ration. As such these factors should be considered when investigating sudden deaths in feedlot lambs that present as intestinal accidents.