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Herniation of a portion of the reticulum through a diaphragmatic rupture causes chronic ruminal tympany, anorexia, and displacement of the heart.
Aetiology
Most cases of diaphragmatic hernia occur because of weakening of the diaphragm by lesions of traumatic reticuloperitonitis, but diaphragmatic rupture can occur independently of a foreign body and congenital defects of the diaphragm may be a cause in some animals. An unusually high incidence of herniation of the reticulum through the diaphragm, sometimes accompanied by the abomasum, has been recorded in water buffalo.
Pathogenesis
The usual syndrome is similar to that of vagus indigestion in which ruminal hypermotility is present. It seems probable that there is either achalasia of the reticulo-omasal sphincter caused by involvement of the vagus nerve or impairment of function of the esophageal groove caused by the fixation of the reticulum to the ventral diaphragm. The disturbance of function in the fore-stomachs suggests that food can get into the rumen but cannot pass from there to the abomasum. The hypermotility is thought to be caused by overdistension of the rumen and to be the cause of frothy bloat.
There is usually no interference with respiration unless major herniation has occurred, but displacement and compression of the heart is common.
Clinical Findings
There is a capricious appetite and loss of condition for several weeks before abdominal distension caused by accumulation of fluid and froth in the rumen, persistent moderate tympany of the rumen, occurs. Grinding of the teeth may occur, and the feces are pasty and reduced in volume. Rumination does not occur but occasionally animals regurgitate when a stomach tube is passed.
The temperature is normal and bradycardia may be present (40–60 beats/min). Breathing is usually normal. A systolic murmur may be present and the intensity of the heart sounds may suggest displacement of the heart, usually anteriorly or to the left. Reticular sounds are audible just posterior to the cardiac area in many normal cows, and they are not significantly increased in diaphragmatic hernia.
A more severe syndrome is recorded in cases in which viscera other than a portion of the reticulum is herniated. Peristaltic sounds may be audible in the thorax and there may be interference with respiration and signs of pain with each reticular contraction. Affected animals usually die of inanition (exhaustion caused by lack of nourishment) in 3 to 4 weeks after the onset of bloat.
Necropsy Findings
The majority of cases are complications of traumatic reticuloperitonitis and a fistulous tract is often found in the vicinity of the diaphragmatic rupture, which is usually 15 to 20 cm in diameter. A portion of the reticulum protrudes into the right pleural cavity to form a spherical distension usually 20 to 30 cm in diameter, but is more extensive in some cases. The reticulum is very tightly adherent to the hernial ring, which is thickened by fibrous tissue. The omasum and abomasum are relatively empty but the rumen is overfilled with frothy, porridge-like material, which contains very little fiber. Less common cases are those in which part of the reticulum, the omasum, and part of the abomasum are herniated.