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in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

Abstract

Objective—To characterize the texture, mineralogic features, and chemical features 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 obstruction and rupture caused by enteroliths. Dietary and environmental history 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. Colonic concentrations of magnesium (Mg), phosphorus (P), sulfur (S), sodium (Na), calcium (Ca), and potassium (K) were determined. Enteroliths were analyzed via electron microprobe analysis and X-ray diffraction.

Results—Enteroliths varied widely regarding degree of porosity, presence and distribution of radiating texture, and composition and size of the central nidus. A distinct concentric banding was identifiable in all enteroliths. Struvite was the predominant component of all enteroliths, although Mg vivianite was identified in 5 enteroliths, and there were variable quantities of Na, S, K, and Ca in the struvite within enteroliths. Despite an abundance of Ca in colonic fluids, Mgphosphate minerals were preferentially formed, compared with Ca-phosphates (apatite), in equine enteroliths.

Conclusions and Clinical Relevance—Enteroliths comprise 2 major Mg phosphates: struvite and Mg vivianite. There is wide variability in macrotexture and ionic concentrations between and within enteroliths. (Am J Vet Res 2001;62:350–358)

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in American Journal of Veterinary Research

Abstract

Objectives—To determine the in vitro effect of prostaglandin E2 (PGE2), PGF, PGI2; and nonsteroidal anti-inflammatory drugs (NSAID; ie, flunixin meglumine, ketoprofen, carprofen, and phenylbutazone) on contractile activity of the equine dorsal colon, ventral colon, and pelvic flexure circular and longitudinal smooth muscle.

Animals—26 healthy horses.

Procedure—Tissue collected from the ventral colon, dorsal colon, and pelvic flexure was cut into strips and mounted in a tissue bath system where contractile strength was determined. Incremental doses of PGE2, PGF, PGI2, flunixin meglumine, carprofen, ketoprofen, and phenylbutazone were added to the baths, and the contractile activity was recorded for each location and orientation of smooth muscle.

Results—In substance P-stimulated tissues, PGE2 and PGF enhanced contractility in the longitudinal smooth muscle with a decrease or no effect on circular smooth muscle activity. Prostaglandin I2 inhibited the circular smooth muscle response with no effect on the longitudinal muscle. The activity of NSAID was predominantly inhibitory regardless of location or muscle orientation.

Conclusions and Clinical Relevance—In the equine large intestine, exogenous prostaglandins had a variable effect on contractile activity, depending on the location in the colon and orientation of the smooth muscle. The administration of NSAID inhibited contractility, with flunixin meglumine generally inducing the most profound inhibition relative to the other NSAID evaluated in substance P-stimulated smooth muscle of the large intestine. The results of this study indicate that prolonged use of NSAID may potentially predispose horses to develop gastrointestinal tract stasis and subsequent impaction. (Am J Vet Res 2000;61:1259–1266)

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in American Journal of Veterinary Research

Objective

To evaluate anatomy of the stifle in llamas and determine outcome of llamas that underwent surgery for repair of patellar luxation.

Design

Anatomic and retrospective study.

Animals

6 llamas with unilateral patellar luxation and 1 llama with bilateral luxations.

Procedure

6 stifles from llama cadavers were dissected to determine anatomy. Medical records were reviewed to identify history, procedure, outcome, and complications of llamas that underwent surgery.

Results

6 llamas had lateral patellar luxation (including the llama with bilateral luxations), and 1 had medial patellar luxation. Six llamas had a history of trauma before onset of clinical signs. Two llamas underwent tibial tuberosity transposition, but luxation recurred in both and 1 had problems with breakage of implants. The other 5 llamas underwent imbrication and release procedures; however, luxation recurred in 4 of the 5. Surgery was repeated in 2 llamas, with successful outcomes.

Clinical Implications

Results suggest that imbrication and release procedures may be useful for correction of patellar luxation in llamas without other bony abnormalities. However, long (20 cm) imbrication and release incisions are needed for a successful outcome. Use of a sling after surgery, to allow a gradual return to weight bearing and exercise, may also be important. (J Am Vet Med Assoc 1998; 212:860-865)

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in Journal of the American Veterinary Medical Association

SUMMARY

The vasculature of the jejunum was studied in 6 llamas and 1 alpaca, using a combination of microangiography, standard light microscopy, and vascular cast imaging. The casts were examined by use of scanning electron microscopy and low-power dissecting microscopy. After administration of 40,000 IU of heparin, all animals were euthanatized by administration of an overdose of sodium pentobarbital. Three sections of jejunum and their respective arcuate vessels were isolated from each animal. One section was immediately placed in formalin for later H&E staining. The second and third sections were placed in warm saline solution, and the vasculature was flushed free of all blood by repeated infusions of the solution. Once flushed of all blood, one section was infused with a radio-opaque medium and subsequently evaluated by microangiography, and the remaining section was perfused with a methylmethacrylate polymer for creation of vascular casts.

The arcuate vessels branched into extensive primary and secondary arcades prior to giving rise to the marginal rete. Muscular arteries and small veins left the marginal rete and penetrated the tunica serosa and tunica muscularis to provide nutrients or drain the mesenteric angle, respectively, or entered into the circumferential submucosal network. The primary penetrating vessels in the submucosa formed an extensive submucosal plexus that supplied the tunica serosa, tunica muscularis, and tunica mucosa. The primary penetrating vessels anastomosed with vessels from oral and aboral sections and with their counterparts from the opposite side at the antimesenteric border. Vessels supplied the tunica serosa and tunia muscularis by branching centrifugally from the submucosal plexus supplying the inner circular and outer longitudinal muscle layers parallel to their respective muscle layers. The arterioles supplying the tunica mucosa branched at right angles, penetrated the muscularis mucosa, and gave rise to clusters of arterioles supplying either the villi or the intervening crypts; anastomosis occurred between these 2 systerns toward the base of the villus. The arterioles gradually developed a discontinuous smooth muscle layer as they approached the base of the villus. Each villus was supplied by a single centrally placed metarteriole that spiraled to the tip of the villus, divided, and descended in a fountaining capillary network. The individual capillaries in the cascade coalesced to drain via 2 to 4 venules at the base of the villus. Branches from the venules entered into an anastomosing network in the lamina propria to drain the crypts. Venules drained in the submucosal plexus and continued paralleling the arterial supply toward the mesenteric border and the arcuate veins. The jejunal vasculature of South American camelids contains an extensive set of anastomotic connections at all levels after formation of the arcuate vessels. Within the scope of this examination into the microvasculature of llamas and alpacas, differences were not detected between the individual species.

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in American Journal of Veterinary Research

Summary

The microvascular circulation of the descending colon was studied in 5 adult horses, using microangiography and light microscopy combined with gross studies and scanning electron microscopy of vascular replicas. After heparinization, horses were euthanatized, and 3 segments of the descending colon and its mesentery containing 1 vascular arcade were removed from each horse. The fecal balls were gently massaged from the lumen, and the blood was flushed free of the circulation with isotonic NaCl.

In 5 segments, the vascular system was injected with a modified radiopaque medium and evaluated radiographically. Specimens examined radiographically also were prepared for histologic examination, using standard methods. Ten segments were injected with 1 of 2 types of plastics and studied grossly or by scanning electron microscopy.

Arcuate arteries gave rise to a descending colonic rete that surrounded the vein and supplied numerous descending colonic lymph nodes. The rete also supplied the mesocolon and the descending colonic tissue. Short filamentous vessels arising from the rete directly penetrated the mesenteric tenia to supply an intermuscular plexus between the longitudinal and circular muscle layers of the muscularis externa. Larger vessels arising from either side of the rete divided into the long- and short-terminal arteries that supplied an extensive submucosal plexus, which was continuous around the circumference. The submucosal plexus supplied the mucosa, the tunica muscularis, and the serosa. Vessels running centrifugally from the submucosal plexus formed an intermuscular plexus between the longitudinal and circular muscle layers of the muscularis externa. The intermuscular plexus at the mesenteric angle also was supplied by vessels branching from the short-terminal arteries as they penetrated the muscularis externa. At the antimesenteric tenia, the submucosal plexus gave rise to larger vessels that formed a subserosal loop. From this loop, 5 vessels penetrated the longitudinal muscle layer to contribute to the intermuscular plexus. Vessels within the longitudinal and circular muscles of the muscularis externa ran parallel to the muscle fibers and, consequently, perpendicular to each other. Arteries supplying the mucosa penetrated the muscularis mucosa and branched into a capillary network at the base of the descending colonic glands. These capillary networks anastomosed with the networks around adjacent glands at the luminal surface, forming a honeycomb like pattern. Drainage was facilitated by more sparsely distributed venules that united with venules from adjacent areas and descended to the submucosal plexus. These veins were characterized by regular, helical, smooth muscle constrictions.

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in American Journal of Veterinary Research

Abstract

Laparoscopy was performed on 6 horses (2 mares, 2 geldings, 2 stallions) to determine the normal laparoscopic anatomy of the equine abdomen. After withholding feed for 36 hours, horses were examined from the left and right paralumbar fossae, and the visceral anatomic structures were recorded by videotape and photography. One mare developed emphysema located subcutaneously at the primary laparoscopic portal; otherwise, there were no complications. The anatomic structures of diagnostic importance that were observed in the left half of the abdomen were the hepatic duct; left lateral and quadrate lobes of the liver; stomach; spleen; left kidney with the associated nephrosplenic ligament; segments of jejunum, descending colon, and ascending colon; left side of the male and female reproductive tracts; urinary bladder; vaginal ring; and mesorchium. Important structures observed in the right side of the abdomen were portions of the common hepatic duct; left lateral, quadrate, and right lobes of the liver; caudate process of the liver; stomach; duodenum; right dorsal colon, epiploic foramen; omental bursa; right kidney; base of the cecum; segments of jejunum, descending colon, and ascending colon; urinary bladder; right half of the male and female reproductive tracts; and rectum.

Free access
in American Journal of Veterinary Research

Summary

Surface oximetry was used to evaluate viability of the ascending colon in 60 horses with naturally occurring colonic volvulus or displacement. Tissue surface oxygen tension (Ps o 2 ) was measured on the serosal surface of the pelvic flexure after anatomic correction of the colonic obstruction. Horses with Ps o 2 > 20 mm of Hg were predicted to have viable colon; whereas, horses with Ps o 2 ≤ 20 mm of Hg were predicted to have nonviable colon. Results of surface oximetry were compared with final outcome. For surface oximetry, sensitivity (ability to accurately identify colon that was nonviable) was 53%, but specificity (ability to accurately identify bowel that was viable) was 100%. Negative predictive value (probability that a horse with Ps o 2 > 20 mm of Hg truly had viable bowel) was 87%, and positive predictive value (probability that a horse with Ps o 2 ≤ 20 mm of Hg truly had nonviable bowel) was 100%. The overall accuracy was 88%. Of the 45 horses that had a colonic Ps o 2 > 20 mm of Hg and survived, 7 had been given, on the basis of subjective assessment of visual criteria, a good prognosis, 28 had been given a guarded prognosis, and 10 had been given a poor prognosis. Of the horses that had a colonic Ps o 2 > 20 mm of Hg but died after surgery because of further colonic infarction, confirmed at necropsy, 4 had been given a poor prognosis, and 3 had been given a guarded prognosis. Of the 8 horses that had a colonic Ps o 2 ≤ 20 mm of Hg and died after surgery, 7 had been given a poor prognosis, and 1 had been given a guarded prognosis. We concluded that surface oximetry, a relatively noninvasive technique, provided a better prediction of survival in horses with colonic volvulus or displacement than did visual inspection alone.

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in Journal of the American Veterinary Medical Association

Summary

The normal microvascular permeability of the ascending colon in horses and the microvascular permeability of that segment after ischemia and reperfusion were investigated. Microvascular permeability was estimated by the ratio of lymphatic protein to plasma protein concentration (Cl/Cp) at high lymph flow rates in 8 adult horses in 2 equal groups: normal and ischemic (2-hour period). Lymphatic flow rates and lymph and plasma protein concentrations were determined. Intestinal biopsy specimens were obtained at the end of each experiment. Flow independent values were selected and compared by one-way anova, and the mean and sem of these values were determined. The mean Cl/Cp ratios for the flow independent part of each data set were as follows: normal = 0.36 ± 0.08; ischemic = 0.70 ± 0.08. These groups were significantly different (P ≤ 0.0001). Microscopic evaluation revealed mild congestion and edema in the normal group. The ischemic group had mild to moderate mucosal degeneration, with moderate to severe congestion and edema. We concluded that ischemia of the ascending colon, when followed by reperfusion, results in a significant increase in microvascular permeability.

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in Journal of the American Veterinary Medical Association