Left displaced abomasum (LDA) is a common gastrointestinal disorder of lactating dairy cattle. Left displaced abomasum, right
displaced abomasum (RDA), and abomasal volvulus (AV) are common abdominal diseases of lactating dairy cows characterized by
varying degrees of abomasal distension and displacement. Impaired abomasal motility and increased accumulation of gas are
considered as prerequisites for development of LDA, RDA, and AV. Many cows with LDA suffer from concurrent disease such as
hepatic lipidosis and inflammatory disorders or bacterial infections such as mastitis, metritis, retained placenta, and pneumonia,
that result in decreased appetite and nutritional stress.
Abomasal emptying rate is decreased in cows with LDA and is further decreased immediately after surgical correction of LDA.
This finding demonstrates the presence of postoperative hypomotility in cows after surgical correction of LDA. Complex pathophysiological
mechanisms contribute to the pathogenesis of post operative hypomotility. Medical treatment of cattle suspected to have abomasal
hypomotility is widely practiced, but until recently, little data was available on treatment efficacy. Because abomasal hypomotility
has been associated with hypocalcaemia, endotoxemia, alkalemia, hyperinsulinemia, and hyperglycemia, the current focus in
treating adult cattle and calves suspected to have abomasal hypomotility is correcting acid-base, electrolyte, and metabolic
abnormalities, combating the effects of endotoxemia, and eliminating gram-negative bacterial infections.
Prokinetic agents have the ability to stimulate, coordinate, and restore gastric, pyloric, and small intestinal motility.
Effective treatment of postoperative hypomotility hastens the return of normal gastrointestinal motility and is a goal of
postoperative management of human patients and horses after abdominal surgery. A variety of drugs have been tested in order
to prevent and treat postoperative hypomotility in animals, these include adrenoceptor antagonists, cholinergic agents such
as carbachol, cisapride, metoclopramide, spasmoanalgesic and anti-inflammatory drugs, epidural local anaesthetics, and intravenous
local anaesthetics. Most of these agents have not been demonstrated to be effective prokinetic agents in cattle. Treatment
of abomasal hypomotility is focused on identifying and resolving the inciting cause, correction of serum electrolyte (particularly
potassium and calcium) and acid-base balance. Once these issues have been addressed, erythromycin (8.8 to 10 mg/kg IM) can
be administered and has been well documented to be the best prokinetic agent in cattle. Erythromycin exerts its effect on
accelerating gastric emptying by acting as a motilin agonist via binding to motilin receptors in the pyloric antrum and proximal
small intestine. Motilin is a 22 amino acid peptide that is periodically released from endocrine cells in the duodeno-jejunal
mucosa, thereby initiating the migrating motor complex of the mammalian gut during the interdigestive period.
Erythromycin (8.8 to 10.0 mg/kg BW IM) accelerates abomasal emptying in healthy preruminant calves, healthy dairy cows, and
lactating cows undergoing surgical correction of LDA. Erythromycin (10 mg/kg IM, once) increases abomasal emptying rate, milk
production, and rumen contraction frequency in the immediate postoperative period in cows undergoing surgical correction of
LDA. Because disturbed abomasal electromyographic activity and diminished abomasal smooth muscle contraction in vitro in cows
with LDA, it is clear that post operative hypomotility is common in cows immediately after surgical correction of LDA. We
do not know the duration of time that abomasal hypomotility remains after surgical correction of LDA.
In a longitudinal ultrasonographic study of adult dairy cows, we observed marked changes in abomasal dimensions and position
during the last 3 months of gestation and first 3 months of lactation. The abomasal length decreased and the width increased
during the last 3 months of gestation, resulting in a more transverse orientation of the abomasum within the abdomen in comparison
to nongravid cattle or cattle in early gestation. Our results therefore support the widely held belief that the gravid uterus
pushes the abomasum into a more transverse and leftwards position on the ventral abdominal wall in comparison to nongravid
cattle or cattle in early gestation.
Abomasal position within the abdomen is dependent on the uterine and ruminal volume, and the changes in abomasal position
we observed during the last 3 months of gestation and first 3 months of lactation support the concept that uterine and ruminal
volume influence abomasal position. However, the observational nature of our study prevented us from determining the relative
importance of changes in uterine and ruminal volume on abomasal position. Within 14 days after parturition the abomasum returned
to a caudal and right sagittal position, similar to that at the beginning of the last 3 months of gestation. Contrary to most
pictorial representations of the shape of the abomasum within a cow's abdomen, results of our study indicated that the abomasum
in adult cows is always wider than it is longer.