Petrographic and geochemic evaluation of equine enteroliths

Objective-To characterize the texture, mineralogic features, and chemical f eatures of enteroliths obtained from horses. Sample Population-Enteroliths from 13 horses with colic. Procedure-Enteroliths were harvested from 13 horses that underwent ventral midline celiotomy for treatment of colic or necropsy because of colonic obs truction and rupture caused by enteroliths. Dietary and environmental histo ry were determined via questionnaires or evaluation of medical records. In 7 horses that underwent surgical treatment for enterolithiasis, samples of colonic contents were obtained via an enterotomy in the pelvic flexure. Col onic concentrations of magnesium (Mg), phosphorus (P), sulfur (S), sodium ( Na), calcium (Ca), and potassium (K) were determined. Enteroliths were anal yzed via electron microprobe analysis and X-ray diffraction. Results-Enteroliths varied widely regarding degree of porosity, presence an d distribution of radiating texture. and composition and size of the centra l nidus. A distinct concentric banding was identifiable in all enteroliths. Struvite was the predominant component of all enteroliths, although Mg viv ianite was identified in 5 enteroliths, and there were variable quantities of Na, S, K, and Ca in the struvite within enteroliths. Despite an abundanc e of Ca in colonic fluids, Mg-phosphate minerals were preferentially formed , compared with Ca-phosphates (apatite), in equine enteroliths. Conclusions and Clinical Relevance-Enteroliths comprise 2 major Mg phosphat es: struvite and Mg vivianite. There is wide variability in macrotexture an d ionic concentrations between and within enteroliths.