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in Journal of the American Veterinary Medical Association
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

Abstract

Objective—To characterize the vascular anatomy of the third compartment of the stomach of llamas.

Animals—7 adult llamas.

Procedure—Immediately after each llama was euthanatized, vascular replicas of tissue from the third compartment were prepared by use of methylmethacrylate monomer and catalyst. Following chemical removal of tissue, the casts were further prepared for examination via scanning electron microscopy. By use of barium solution, microangiography was also performed on fixed tissue samples; the infused tissue was sectioned and imaged radiographically. Tissue samples were also collected for histologic evaluation after fixation and H&E staining.

Results—The third compartment was supplied by 4 pairs of primary arteries and veins located around the circumference of the structure. From these vessels, smaller arteries and veins branched to supply the serosal surface and penetrated deeper through the tunica muscularis to supply the submucosal and mucosal layers. An extensive capillary network was arranged in a hexagonal array surrounding the gastric glands, such that the mucosal aspect of the replicas had a honeycomb-like appearance. Histologically, variably sized villous projections lined by a single layer of epithelial cells with an extensive glandular network were observed.

Conclusions and Clinical Relevance—The third compartment of the stomach of llamas is a highly vascular structure with an extensive anastomotic capillary network at the luminal surface. Branching vessels provide extensive collateral circulation, and it appears that surgical incisions should heal well. Incisions in the third compartment should be oriented parallel to the longitudinal plane. (Am J Vet Res 2003; 64:346–350)

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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.

Free access
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.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To develop an objective, accurate method for quantifying forelimb ground reaction forces in horses by adapting a human in-shoe pressure measurement system and determine the reliability of the system for shod and unshod horses.

Animals—6 adult Thoroughbreds.

Procedure—Horses were instrumented with a human in-shoe pressure measurement system and evaluated at a trot (3 m/s) on a motorized treadmill. Maximum force, stance time, and peak contact area were evaluated for shod and unshod horses. Three trials were performed for shod and unshod horses, and differences in the measured values were examined with a mixed model ANOVA for repeated measures. Sensor accuracy was evaluated by correlating measured variables to clinically observed lameness and by a variance component analysis.

Results—4 of 6 horses were determined to be lame in a forelimb on the basis of clinical examination and measured values from the system. No significant differences were observed between shod and unshod horses for maximum force and stance time. A significant decrease in peak contact area was observed for shod and unshod horses at each successive trial. Maximum force measurements provided the highest correlation for detecting lameness ( r = 0.91, shod horses; r = 1.0, unshod horses). A variance component analysis revealed that 3 trials provided a variance of 35.35 kg for maximum force (± 5.78% accuracy), 0.007 seconds for stance time (± 2.5% accuracy), and 8.58 cm2 for peak contact area (± 11.95% accuracy).

Conclusions and Clinical Relevance—The in-shoe pressure measurement system provides an accurate, objective, and effective method to evaluate lameness in horses. ( Am J Vet Res 2001;62:23–28)

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in American Journal of Veterinary Research