The large size of modern sheep and Work Health Safety concerns has led to the increasingly common practice of sedating rams before they are shorn.
Xylazine hydrochloride and acepromazine maleate are commonly prescribed. This is generally seen to be a safe practice and thought to be beneficial for the sheep and sheep handlers. An unexpected death in a ram after sedation and shearing was investigated to determine the cause of death.
The diagnosis at autopsy was that death was due to intestinal torsion.
A producer had not previously used sedation as an aid to shearing rams.
Eleven rams were sedated with 10mg xylazine each prior to being shorn. The prescribed dose was at the low end of the label recommended range. (Approximately 0.1mg/kg with an intramuscular dose range of 0.1-0.3mg/kg)
There was a range of responses to sedation in the rams. Most rams were relaxed to a degree and none became recumbent. The two largest rams appeared the most sedated. One ram had remained bright and alert and jumped 2 internal pens after sedation. As they were sedated, each ram was marked, so that it should not have been possible to dose any ram twice, or miss dosing a ram.
The rams had grazed lush green grass dominant improved pasture then for the day or so before shearing, they grazed around the shearing shed and yard which contained areas of tall lush grass and lush weeds such as capeweed and marshmallow.
The rams were fasted overnight prior to shearing.
Immediately after shearing one ram was noticed to be lying down in the pens and did not rise as the others moved out. He was moved to an isolation pen and found dead 4 hours later. The dead ram's initial response to sedation was unknown. It could not be determined whether this ram had been the one to become excitable and poorly sedated prior to shearing, or whether it was one of the more sedated rams.
The dead ram was a well grown mature Poll Dorset in good body condition with an estimated weight of 100-120 kg. The abdomen was distended and the oral mucous membranes were white. There was no nasal discharge. It was presented in right lateral recumbency.
An autopsy was performed. A midline abdominal incision revealed serosanguinous peritoneal fluid, distended dark red loops of small intestine and distended reddened large intestine.
The rumen was distended with gas and green foamy ingesta. The chest cavity was normal. A gross pathological diagnosis of intestinal torsion was made and the cause of death determined to be from shock.
As the producer had more rams to shear, it was recommended that he reduced the amount of rapidly digestible feed in the diet by increasing fibre in the ration. It was recommended that hay be fed for a day or two to the remaining rams. After 2-3 days of hay supplementation the remaining 90 rams were sedated and shorn with no further losses or incidents.
Intestinal Torsion or "Red gut" in sheep are terms used synonymously5 for a rapidly fatal condition of twisting of the intestinal mass around the mesenteric blood supply in the long axis of the mesentery and subsequent occlusion of the cranial mesenteric artery and vein.6 7 8
Death follows rapidly in 2 to12 hours.6 7 Most cases are found dead. The condition has been reproduced experimentally in sheep by ligating the mesenteric artery and vein, including ileocolic tributaries.1 Death is due to shock, evidenced by falling arterial pressure and developing haemoconcentration in experimentally produced cases.1
Naturally occurring cases may show brief signs of abdominal distension and discomfort before recumbence and death.6 7 The small intestine and large intestine are discoloured and reddened from approximately 100-200cm from the pyloris to the lumbar flexure of the colon, which is the length of the gastrointestinal tract supplied by the anterior or cranial mesenteric artery.1 5
Once conditions occur to occlude the blood supply to the intestine, hypoxia rapidly causes necrosis of all layers of the intestinal wall beginning by affecting the intestinal villi within 10 minutes and continuing to sloughing and necrosis of the epithelium within 4-5 hours.8 There is a brief hyperexcitability of muscle followed by loss of contractility.8 Torsion causes effusion of fluid and blood into the intestinal lumen as the mucosal integrity is lost.8 Anaerobes produce toxins that have systemic effects on cardiovascular function.8
Red gut is normally a sporadic condition in sheep6 and a relatively rare condition in Australia.3 It was first reported in the 1960s in Scotland and then in New Zealand occurring as an outbreak form in rapidly growing lambs on lucerne pasture.6 Red gut is sometimes seen as a cause of death in weaned lambs grazing lucerne in the Hume LHPA. It has also been reported to occur in lambs grazing clover pastures in Australia.6
Intestinal torsion does occur rarely in cattle and has also been reported in goats and in weaner bulls on lucerne.6 It is seen more commonly in suckling kids, lambs and calves raised on an artificial diet.6 8
Red gut is believed to be associated with conditions that cause a reduction in size of the reticulorumen and a simultaneous increase in the size of the hindgut and caecum in sheep5 6. This can be seen on lambs grazing lucerne and clover pastures.7 This is thought to allow for more mobility of the intestinal mass and an abnormal position of small and large intestine can result.5 6 It is thought that torsion can follow once displacement has occurred.7
It is theorised that this combination of reduced rumen size and increased large intestine size can occur when rapidly digestible feed moves quickly from the rumen into the intestine.6 If this occurs conditions in the large intestine could allow continuing fermentation and gas production.6 In suckling hand raised ruminants it is suggested that highly digestible food that is ingested rapidly may predispose to intestinal gas formation and hypermotility.8 A more motile distended caecum could contribute to abdominal organ displacement.6
Grazing roughage has a protective effect against the development of red gut, and providing access to more mature fibrous feed or hay, or changing to intermittent grazing of highly digestible feeds, can prevent further cases when the condition occurs.6 7
Physical manipulation of at risk animals may play a role on occasion in cases of intestinal torsion. Intestinal torsion has been reported associated with rolling cattle to replace a uterine torsion or to correct abomasal displacement.6 Manipulation of the ram for shearing could have been a factor in the development of intestinal torsion in this case.
The abnormal excitatory behaviour of one ram following xylazine sedation, and lack of response to sedation, could indicate that a painful condition was present prior to sedation and shearing in that ram. Xylazine is an alpha 2 agonist and failure to achieve sedation may be due to pre existing pain, stress, fear or excitement.9
Xylazine is generally considered to be a drug that produces reliable sedation with some analgesia and muscle relaxation.9 However, xylazine given pre-shearing can normally produce varied degrees of sedation in rams, not necessarily well explained by dose rate differences.2
Effects of xylazine include depression of the central nervous system, respiratory depression, bradycardia, hypertension, hypotension, tachycardia and ventricular arythmias.4 Ruminants are considered more sensitive to xylazine than many species and gastrointestinal effects include decreased gut motility, inhibition of reticuloruminal contractions and prolonged gastrointestinal transit time.4
In this case the rams had been grazing high moisture content, highly digestible forage and then fasted for 12 hours prior to shearing. It would be possible for rapidly digestible ingesta to be emptying from the rumen (reducing rumen volume) and still have significant volume and fermentation occurring in the large intestine after a 12 hour fast. Manipulation of the ram to shear it under these conditions may have contributed to gut displacement.
Sedation of rams for shearing is widely used in the sheep industry with few reported deaths of rams occurring as a result. Some issues due to altered ability of sedated rams to thermoregulate are well recorded. The conditions on the day were mild and thermoregulation was not considered to be a factor this case.
Intestinal torsion is a rare condition in adult ruminants. This case appears to be an isolated case and an unusual cause of death in an adult ram.