Left displacement of the abomasum (LDA) is an economically important condition commonly encountered by the dairy practitioner. Abomasal displacement was either not present or not diagnosed prior to the early 1950?s, when the first reports appeared. The risk of developing an LDA is greater in highproducing cows from intensively managed herds, adding LDA to the list of production diseases that plagues the modern dairy cow. The incidence in problem herds may range as high as 20%, and in 80% of cases, affected cows have calved within the past month.

Despite the frequency of occurrence of LDA, its precise etiology remains unclear. The four most popular theories regarding its etiology are: the dietary theory, which correlates a high concentrate, low fiber diet with depression of rumen contractions and eructations as well as increased rurnen acidity, all of which predispose to LDA; the mechanical theory, in which the elevation of the rumen by the pregnant uterus is proposed to allow the abomasum to shift ventrally and leftward, becoming trapped on the left when parturition produces a sudden topographic change in the abdomen; the genetic theory, which argues that genetic seictiori for broader, larger dairy cows has produced animals more prone to LDA development due to greater abdominal capacity; and the hypotonia/atonia theory, which is the most comprehensive and includes the important and generally well-accepted dietary theory. The hypotonia theory maintains that any cause of dcreased abomasal tone can predispose to displacement.