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in Journal of the American Veterinary Medical Association

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

Summary

The microvascular anatomic features of the small intestine was described by correlating results of microangiography, light microscopy, gross studies, and scanning electron microscopy of vascular replicas in 14 horses. After heparinization, the horses were euthanatized, a length of jejunum was transected, and blood was flushed free of the circulation, using isotonic NaCl solution. In six horses, the circulatory system was perfused with a modified radiopaque medium and evaluated radiographically. These sections were then evaluated by standard histologic methods. Sections from 8 horses were perfused with 1 of 2 types of plastics and studied grossly or by scanning electron microscopy.

The margined arterial arcade gives rise to vessels that enter the jejunum at the mesenteric angle. These vessels penetrated either directly, by branching and entering on both sides of the mesenteric angle, or supplying only 1 side of the mesenteric angle. All these vessels continued in the submucosa branching extensively, forming a submucosal plexus. This submucosal plexus supplied the tunica muscularis, tunica serosa, and the mucosa. Vessels within the 2 muscle layers ran parallel to the muscle fibers and, consequently, perpendicular to each other. The arterial supply to the mucosa penetrated the muscularis mucosae and branched to supply 2 mucosal capillary networks. An eccentrically placed arteriole penetrated the base of the villus and spiralled to the tip where it "fountained" into a mesh-like capillary network, which descended peripherally in the villus to drain via 1 to 3, but most commonly 2 venules. Venules from adjacent villi united and drained via the submucosal veins. The second capillary network supplied the glands of the intestinal crypts. The capillary network around adjacent glands anastomosed just below the luminal surface. There were connections between this network and the base of the villus capillary network. Drainage of the glandular capillary network was through these connections and through the villus venules. There was no evidence of arterovenous anastomoses.

Free access
in American Journal of Veterinary Research

Summary

The microvascular circulation of the cecum was studied in 15 adult horses, using microangiography and light microscopy combined with gross studies and scanning electron microscopy of vascular replicas. After heparinization, the horses were euthanatized and the cecum was transected at the cecocolic junction. Blood was flushed free of the circulation with isotonic NaCl and the cecal lumen was slightly distended. In 6 horses, the vascular system was injected with a modified radiopaque medium and evaluated radiographically. Sections evaluated radiographically were also prepared for histologic examination by standard methods. Eight horses were injected with 1 of 2 types of plastics and studied grossly or by scanning electron microscopy. In 1 additional horse, the lateral and medial arteries were injected with different colored plastic for gross studies.

The lateral and medial cecal arteries appear to supply the respective areas of the cecum with minimal mixing of the 2 circulations. The major vascular supply to the cecal apex appeared to be through the medial cecal artery. Both the lateral and medial cecal arteries gave rise to cecal retia, which formed a mesh-like network around the respective veins. Vessels from these retia supplied the cecal tissue and the cecal lymph nodes. The continuation of the retia was through long terminal arteries that coursed around the circumference in the submucosa, forming an extensive submucosal plexus. This plexus supplied both the mucosa, and the tunica muscularis and serosa. Vessels within the longitudinal and circular muscle layers of the muscularis externa ran parallel to the muscle fibers, and consequently, perpendicular to each other. Arteries supplying the mucosa branched into a capillary network as they penetrated the muscularis mucosa at the base of the cecal 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 veins. These veins were characterized by regular helical smooth muscle constrictions.

Free access
in American Journal of Veterinary Research

Abstract

Objectives—To determine whether quantitative analysis of sonographic brightness could be used to detect healing of an induced injury of the superficial digital flexor tendon in horses and whether rate of healing was influenced by equine recombinant growth hormone.

Animals—8 clinically normal Standardbreds.

Procedures—A localized injury was created in the left and right superficial digital flexor tendons of each horse by injection of 2,000 units of collagenase. After injury, 4 horses received equine recombinant growth hormone, a possible promoter of tendon healing. Sonographic images (7.5 MHz) of the flexor tendons and ligaments of the metacarpal region were recorded on videotape prior to injury and weekly for 7 weeks after injury. Images were digitized, and sonographic brightness of tendons and ligaments was calculated.

Results—Collagenase-induced injury was sonographically similar to naturally occurring injury. After injury, sonographic brightness of the tendon decreased; after 3 weeks, brightness progressively increased, although by 7 weeks brightness had not returned to preinjury value. Equine recombinant growth hormone had no significant effect on the rate of tendon healing, as evaluated sonographically or at necropsy.

Conclusions and Clinical Relevance—As healing developed, alterations in sonographic brightness of injured tendons coincided with real changes in tendon structure. Quantitative sonographic brightness could be used to accurately monitor healing of equine tendon and ligament injuries and investigate the efficacy of various treatment regimens. (Am J Vet Res 2001;62:1320–1327)

Full access
in American Journal of Veterinary Research

Abstract

Objectives

To measure blood selenium concentration and glutathione peroxidase (GSH-Px) activity and serum concentrations of vitamin A and α-tocopherol, and to determine the correlation between blood selenium concentration and GSH-Px activity of llamas fed alfalfa hay.

Design

Mean (± SD) serum vitamin A and α-tocopherol concentrations, blood selenium concentrations, and GSH-Px activity were calculated from 9 sequential blood samples collected from llamas fed a diet of alfalfa hay.

Animals

15 clinically normal llamas (8 males, 7 females) between 10 and 14 months of age.

Procedure

Llamas were fed alfalfa hay for 40 days prior to sample collection and then for the duration of the trial. Vitamin E, selenium, and concentrations of vitamin A precursors were measured in the hay. Blood samples were collected on days 0, 6, 7, 9, 13, 20, 42, 64, and 98. Blood selenium concentrations were measured, using an inductively coupled spectrometric method. Blood GSH-Px activity was measured with a spectrophotometer, using a modification of a previously described assay. Isocratic high-performance liquid chromatography with florescent detection was used to determine serum α-tocopherol and vitamin A concentrations.

Results

The alfalfa hay contained 0.2 mg/kg of selenium, 5 mg/kg of vitamin E, and 0.9 mg/kg of vitamin A precursors. The mean (± SD) blood selenium concentration and GSH-Px activity were 0.179 ± 0.032 pg/ml and 25.76 ± 6.53 mU NADPH oxidized/min/mg of Hb, respectively, with a correlation coefficient of 0.97. The mean (± SD) concentrations for serum α-tocopherol and vitamin A were 128.1 ± 41.7 and 74.8 ± 5.5 μg/dl, respectively.

Conclusions

Blood selenium concentrations in llamas are highly correlated to GSH-Px activity. Blood selenium concentrations in llamas appear to be similar to other domestic ruminants and diets containing 0.2 mg/kg of selenium appear to provide an adequate dietary source. The concentrations of vitamin A precursors and vitamin E in the hay were below currently recommended dietary levels for llamas, and alfalfa hay appears to provide an unreliable source of vitamins A and E in this species. Further studies are required to determine optimal dietary concentrations and to substantiate a reference range for these vitamins in llamas. (Am J Vet Res 1996; 57:689–692)

Free access
in American Journal of Veterinary Research

Summary

To quantify some components of prepurchase evaluations in horses, records from 134 evaluations performed during a 2-year period were reviewed and the outcome was determined via telephone follow-up interview. Sixty-two percent of the prepurchase evaluations had been performed at the clinic and 38% had been performed in the field by the ambulatory service. All evaluations included physical and lameness examinations, whereas radiography (49%), endoscopy (15%), nerve blocking (5%), transrectal palpation (3%), hematologic analysis (2%), electrocardiography (2%), drug testing for analgesic agents (2%), and ultrasonography of the flexor tendons (1%) were not always performed. Fifty-nine percent of horses evaluated at the clinic were radiographed, compared with 33% of horses evaluated in the field (P < 0.05).

Thirty-seven percent of horses evaluated were judged serviceable for their intended use. Thirty-five percent of horses evaluated at the clinic were assessed to be serviceable, compared with 41% of those evaluated in the field (P < 0.05). Horses used for pleasure riding (48%) tended to be considered serviceable more often than horses used for more athletic endeavors (3-day eventing, 33%; hunter/jumper, 24%; show, 31%; dressage, 30%). The most common basis for finding a horse unserviceable was lameness (88%).

On the basis of a telephone interview, horses were divided into 5 groups: horses determined unserviceable on evaluation and not purchased (n = 40); horses determined unserviceable on evaluation, purchased, and then found serviceable on follow-up interview (n = 35); horses determined unserviceable on evaluation, purchased, and then found unserviceable on follow-up interview (n = 9); horses determined serviceable on evaluation, purchased, and found serviceable on follow-up interview (n = 42); and horses determined serviceable on evaluation, purchased, and found unserviceable on follow-up interview (n = 8).

The buyer and seller were present at the evaluation in 34% of cases. The buyer alone was present in 57% of cases, the seller alone in 4% of cases, whereas neither was present in 6% of cases. The potential buyer had used the horse for its intended purpose prior to the prepurchase evaluation in 39% of cases for a mean time of 20.5 days, but this did not appear to affect the serviceability of the horse on follow-up evaluation. Five horses that were leased for > 6 months prior to purchase were all serviceable on follow-up interview, irrespective of the findings at the time of the prepurchase evaluation.

There was a tendency for the value of horses examined at the clinic to be higher than those evaluated by the ambulatory service. The price paid by the buyer was reduced through negotiations on the basis of the prepurchase evaluation in 6% of cases.

Lameness was seen only in horses within the unserviceable group. Lameness tended to be seen more often in horses valued > $2,500 (61%, 46/75) than in horses valued ≤ $2,500 (48%, 28/59). Lameness was associated with 92% (22/24) of horses valued at > $2,500 within the group judged to be unserviceable and not purchased.

Radiography was performed to investigate a specific lameness in 24% (32/134) of evaluations and for survey purposes in 25% (34/134) of evaluations. Of horses radiographed within the unserviceable group, radiography commonly was performed for specific lameness (84%, 32/38) and rarely for survey purposes (24%, 9/38), whereas only survey radiographs were obtained from the serviceable group because no horses exhibited a specific lameness. Radiography was significantly (P < 0.05) more likely to have been performed in horses valued > $2,500 (65%, 49/75) than in those valued < $2,500 (29%, 17/59), and this trend was reflected in all categories. For survey radiographs, the combination of tarsi and bilateral distal forelimbs was the most commonly radiographed area (44%). Bilateral distal forelimbs alone were the second most commonly radiographed area (41%).

A written report summarizing the findings of the evaluation was furnished in 24% of cases. At the time of follow-up interview, 75% of buyers indicated that they would have liked a written report.

Free access
in Journal of the American Veterinary Medical Association

Summary

The signalment, clinical and laboratory findings of surgical conditions, treatment, and outcome of 102 cases of descending colon disease in horses were reviewed. Abnormal conditions were categorized as enteroliths, impactions, strangulating lipomas, fecaliths, foreign body obstruction, volvulus, nephrosplenic entrapment, and other conditions. Eleven breed categories of horses were seen during this period. Arabians, ponies, and American miniature horses were more predisposed to descending colon disease than other breeds (P < 0.05). Female horses and animals >15 years old were more likely to be affected with descending colon disease, whereas horses <5 years old were less likely to be affected (P < 0.05). More specifically, Arabians, Quarter Horses, and Thoroughbreds >10 years old were breeds that were overrepresented when compared with the hospital population (P < 0.05). Enteroliths were most commonly seen in horses between 5 and 10 years old (P < 0.05) and were not seen in horses <2 years old. Enteroliths had a tendency to develop more commonly in Arabians and in female horses. Impactions affected horses >15 years old (P < 0.05) and had a greater tendency to affect ponies and American miniature horses. Female horses were more commonly affected by impaction than were males. Strangulating lipomas were commonly seen in horses >15 years old (P < 0.05) and more specifically female Quarter Horses (P < 0.05). Fecaliths tended to be a disease of horses <1 year old or >15years old and affected males more commonly than females. Ponies, American miniature horses, mixed-breed horses, and mustangs were the breeds most commonly affected. Surgical conditions were categorized as vascular (16%) or nonvascular (84%) conditions. Vascular conditions included strangulating lipomas (6%) and other conditions (10%). Nonvascular conditions included enteroliths (40%), impactions (25%), fecaliths (13%), and other conditions (6%). Horses with vascular lesions were older than horses with nonvascular conditions (P < 0.05). Peritoneal fluid values were high for all surgical conditions of the descending colon. Nucleated cell count and total protein concentration in peritoneal fluid retrieved from horses with vascular lesions were higher than in horses with nonvascular lesions (P < 0.01). Palpation per rectum revealed abnormal findings more commonly in horses with vascular compromise (P < 0.05). Of those horses taken to surgery, 91% were recovered from anesthesia and discharged; 90% of horses, for which the condition was monitored to at least 6 months after surgery, were alive. All horses that were medically treated were alive at least 6 months after discharge.

Free access
in Journal of the American Veterinary Medical Association