Displaced Abomasum

Also known as:

Twisted stomach LDA RDA

Description

This is much less dramatic than a displaced stomach in the dog, and develops chronically. The abomasum is the fourth stomach of the cow and hangs loosely by the omentum. It can move from its normal position to left displcement where it becomes trapped under the rumen or a right displacement which may result in abomasal volvulus and torsion. Rearrangement of abdominal viscera in pregnancy is thought to be an important aetiological factor, however reduced abomasal motility is thought to be the primary aetiological cause. Once the abomasum is displaced gas production by the organ continues causing distension and further displacement.

Signalment

A disease of the cow affecting mainly high yielding dairy cows on high concentrate diets. Usually occurs in the first 6 weeks of lactation. Sometimes displacement does occur before calving, this is in late gestation and accounts for 5% of cases.

Diagnosis

Diagnosis is made on history and clinical signs in combination with auscultation findings. Using a stethoscope the entire left and right flank should be percussed. Over the region of displacement a distinct ping will be heard. Once a ping is identified the stethoscope shoud be held over that area whist balloting the lower flank, this creates a splashing sound at the gas fluid interface which is heard as a tinkle. This confirms the presence of a displaced abomasum.

History and Clinical Signs

A typical history would be a recently calved cow with a sudden drop in appetite and milk production. Animals display general malaise and abdominal pain. On clinical exam a rapid loss of condition may be evident, ketosis or decreased ruminal activity on ausculatation. Often the left flank bulges behind ribs and the temperature may be normal or slightly raised.

Pathogenesis

There are two manifestations of abomasal displacemet. In both the abomasum becomes trapped between rumen and abdominal wall. The more comon presentation is the left displacement (LDA) which is Ventral and to the left of the rumen. The omasum, reticulum and liver are also displaced. Abomasal atony and increased gas production leads to displacement. Factors reducing abomasal motility include a high concentrate diet, increased volatile fatty acids from the rumen and periparturient disease e.g ketosis, hypocalcaemia and metritis. Displacement to the left results in a reduced flow of ingesta as well as reduced digestion resulting in anorexia and dehydration.

A displacement to the right an RDA is less common. Decreased abomasal motility, distension and displacement occurs as in the LDA. Rotation of the abomasum on its mesenteric axis leads to volvulus and constriction of blood vessels and trauma to the vagus nerve resulting in abomasal distenstion with blood-stained fluid and gas, congested mucosa and necrosis of the abomasum, dehydration and circulatory collapse. Additionally the abomasum may rupture, causing peritonitis, shock and death.

Laboratory Tests

Often a severe ketosis is present resulting in raised blood butyrate. If electrolyte levels and blood gas are measured affected animals develop a hypochloraemia and metabolic alkalosis due to reduced outflow of ingesta from the abomasum combined with contined secretion of hydrochloric acid into the abomasum. Hypokalaemia also develops due to the alkalosis which drives potassium into cells combined with a reduced intake due to anorexia.

Treatment

Any concurrent diseases should be treated e.g hypocalcaemia, metritis, mastitis or ketosis. Conservative management can be attempted in low value animals. Rolling can be undertaken to try and manipulate the abomasum into the correct position. This technique involves casting the cow onto her right side and rolling her over whilst percussing and balloting the pings to track the movement of the gas filled abomasum. Reoccurence is likely and success rates with this are usually 30-50%.

A number of surgical techniques are documented to correct the displacement. These include:

• Blind toggle abomasopexy

Toggles are useful in low value animals as it is a cheap and fast technique. The animal is cast and rolled onto her back. Two toggles are inserted through the ventral abdominal wall into the abomasal lumen. Once positioned the two toggles are tied together. Following this blind suture it is possible to toggle the incorrect area (e.g. rumen, reticulum) resulting in fatal complications. To avoid this complication a pH strip can be used to confirm the correct location following cannulation before the toggles are put in place.

• Right flank omentopexy

The right flank is incised one hands distance behind the last rib and the displaced abomasum is located. The organ is then deflated and repositioned in the correct location. The abomasum is sutured to the abdominal wall and the incision is closed in a routine manor.

• Left flank omentopexy

The left flank is incised just caudal to the last rib and the omentum adjacent to the abomasum is located. A long nylon suture is passed through the fat a few times and then both ends through separate points on the ventral body wall. An assistant can help locate the correct position for the suture to be passed by palpating the region with a pair of artey forceps. The two pieces of suture are tied externally and hold the abomasum in the correct position whilst adhesions form.

• Right paramedian abomasopexy

For this technique the cow is sedated and cast onto her back. An incision is made to the right of midline caudal to the most posterior part of the sternum. The abomasum is located, repositioned and sutured to the body wall.

It is important for all surgical techniques that post-operatively the cow is given a large amount of roughage and concentrates are introduced into the diet slowly.

Prevention

On farms with a high incidence of LDAs or RDAs it is likely that there is a problem with the diet of cows in early lactation and this should be addressed. Overall cases can be reduced by maintaining adequate roughage intake, avoiding a rapid decrease in rumen volume following calving, preventing rapid dietary changes and postparturient illness( hypocalcaemia, ketosis, metritis).

Prognosis

Following surgical correction of an uncomplicated displacement sucess rates can reach 95%. Abomasomal volvulus and the presence of an abomasal ulcer are associated with a much poorer prognosis. Additionally tachycardia, decreased temperature, black faeces and a long period of illness are all associated with poorer outcomes.

References

Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial

Andrews, A.H, Blowey, R.W, Boyd, H and Eddy, R.G. (2004) Bovine Medicine (Second edition), Blackwell Publishing