Dorsal Colon Research Articles

Gene Expression Analysis before and after the Pelvic Flexure in the Epithelium of the Equine Hindgut.

Previous research demonstrated the distribution of distinct microbial communities in the equine hindgut surrounding the pelvic flexure. The current study evaluated gene expression in epithelial tissues surrounding the pelvic flexure to characterize patterns that might correlate with microbial distribution. Gene expression was determined by analyzing RNA sequence data from the pelvic flexure, the left and right ventral colon, and the left and right dorsal colon. An average of 18,330 genes were expressed across the five tissues sampled. Most of the genes showed some level of expression in all five tissues. Tissue-restricted patterns of expression were also observed. Genes with restricted expression in the left ventral and left dorsal colons have communication, signaling, and regulatory functions that correlate with their known physiology. In contrast, genes expressed exclusively in the pelvic flexure have diverse functions. The ontology of genes differentially expressed between the pelvic flexure and the surrounding tissues was associated with immune functions and signaling processes. Despite being non-significant, these enrichment trends were reinforced by the functions of statistically significant expression differences between tissues of the hindgut. These results provide insight into the physiology of the equine hindgut epithelium that might influence the microbiota and its distribution.

Traumatic nasogastric intubation as a suspected cause of laryngeal obstruction in a horse recovering from emergency laparotomy

AbstractAn 18‐year‐old mare, admitted for colic, underwent an exploratory laparotomy for right dorsal colon displacement. During recovery from anaesthesia, a severe acute onset laryngeal obstruction occurred at standing, requiring orotracheal re‐intubation, which relieved the obstruction. This was followed by secondary pulmonary oedema, treated with furosemide (2 mg/kg intravenously) and oxygen. At re‐extubation, attempted 30 minutes later, the horse re‐obstructed immediately and collapsed, prompting an emergency tracheostomy. Furosemide (2 mg/kg intravenously) and dexamethasone (0.1 mg/kg intravenously) were also administered. The horse stood up thereafter with a patent airway. In the history, to note, nasogastric intubation was particularly difficult at admission, and was identified as a potential cause of laryngeal trauma that may have precipitated laryngeal obstruction due to severe local inflammation. Dynamic laryngeal collapse probably also played a role due to high inspiratory negative pressure generated at the precise timing of standing, similar to exercise.

Evaluation of gastrointestinal tract lesions and serum malondialdehyde levels after repeated oral administration of phenylbutazone in horses

Phenylbutazone (PBZ) is a widely used nonsteroidal anti-inflammatory drug for horses. However, because of its gastrointestinal side effects, its administration requires careful attention in veterinary practice. Malondialdehyde (MDA) is a serum biomarker associated with increased damage to the equine gastrointestinal system. This study investigated the hematological effects and alterations in the gastrointestinal tract and assessed serum MDA concentrations following repeated oral PBZ administration at clinical doses. Fourteen horses were randomly divided into control and treatment groups. All horses in the treatment group were administered 4.4 milligrams per kilogram of body weight of PBZ syrup orally twice a day for 7 days, whereas the control group received syrup as a placebo. The development of gastrointestinal side effects was investigated using gastroscopy, abdominal ultrasound, and fecal pH; serum MDA concentrations were assessed using a commercially available enzyme-linked immunosorbent assay kit. Data were compared between PBZ-treated and control horses before and after the treatment period. The treatment group exhibited decreased albumin and total protein concentrations. Moreover, this group exhibited a higher thickness of the right dorsal colon wall (p = 0.03) and had higher scores for squamous gastric ulcers (p = 0.01). Fecal pH was lower in the treatment group than in the control group after PBZ administration (p < 0.01). Although MDA concentrations were higher in the treatment group after PBZ administration, they did not differ significantly from those of the control group. This study highlighted the changes in hematological and gastrointestinal lesions resulting from PBZ administration in horses at clinical doses, even without clinical signs. However, MDA may not be an optimal biomarker for the early detection of gastrointestinal damage due to PBZ treatment in horses.

Molecular species determination of cyathostomins from horses in Ireland

Cyathostomins are globally important equine parasites, responsible for both chronic and acute pathogenic effects. The occurrence of mixed infections with numerous cyathostomin species hinders our understanding of parasite epidemiology, host-parasite dynamics, and species pathogenicity. There have been few studies of cyathostomin species occurring in horses in Ireland, where temperate climatic conditions with year-round rainfall provide suitable conditions for infection of grazing animals with bursate nematodes. Here, we amplified and sequenced the ITS-2 region of adult worms harvested at post-mortem from eleven adult horses between August 2018 and June 2020, and recorded species prevalence and abundance of worms recovered from the caecum, right ventral colon and left dorsal colon, using both BLAST and IDTAXA for taxonomic attribution. Phylogenetic relationships and community composition were also recorded and compared with other relevant studies, including a global meta-analysis. Overall, our results agree with previous studies that there does not seem to be a major difference in cyathostomin species occurrence in equids in different geographical regions. We confirmed the results of other workers in relation to the difficulties in discriminating between Cylicostephanus calicatus and Coronocyclus coronatus on the basis of ITS-2 sequences.

Microbiota characterization throughout the digestive tract of horses fed a high-fiber vs. a high-starch diet.

Diet is one of the main factors influencing the intestinal microbiota in horses, yet a systematic characterization of the microbiota along the length of the digestive tract in clinically healthy horses, homogenous for age and breed and receiving a specific diet is lacking. The study used 16S rRNA amplicon sequencing to characterize the microbiota of the intestinal tracts of 19 healthy Bardigiano horses of 14.3 ± 0.7 months of age fed one of two diets. Nine horses received a high-starch diet (HS), and ten horses received a high-fiber diet (HF). After 129 days, the horses were slaughtered, and samples were collected from the different intestinal tract compartments. The microbiota alpha diversity indices were lower in the caecum, pelvic flexure and right dorsal colon of the horses fed the HS diet (False Discovery Rate, FDR < 0.05). The values of beta diversity indicated significant compositional differences between the studied intestinal tract compartments according to the diet received (FDR < 0.05). At the lower taxonomic level (genus or family), the HS diet was associated with a higher relative frequency of Enterobacteriaceae within the small intestine (jejunum and duodenum) (FDR < 0.05). Within the hindgut (caecum and sternal flexure), the HS diet was associated with lower relative frequencies (i.e., a smaller core community) of bacteria belonging to Fibrobacteraceae and Prevotellaceae (FDR < 0.05). Moreover, horses fed the HS diet displayed a higher relative abundance of Streptococcus in the caecum (FDR < 0.05) and Fusobacterium in the sternal flexure (FDR < 0.05), both of which are pathogenic bacteria responsible for inflammation diseases. Samples collected from the pelvic flexure and rectum of horses fed the HS diet showed significantly higher relative frequencies of Succinivibrionaceae (FDR < 0.05) - amylolytic bacteria associated with acidosis. The relative frequencies of the Lachnospiraceae and Ruminococcaceae were lower in the feces collected from the rectum of horses receiving the HS diet vs. HF diet, indicating smaller core communities of these bacteria (FDR < 0.05). Fibrous diets should be promoted to prevent dysbiosis of the microbiota associated with high-starch diet.

Nonsteroidal antiinflammatory drugs reduce anion secretion and increase apoptosis in equine colonic mucosa ex vivo.

Right dorsal colitis causes chronic colic associated with long-term treatment with nonsteroidal antiinflammatory drugs (NSAIDs). This study was designed to determine if NSAIDs could inhibit anion transporters that protect against intestinal mucosal injury in other species. 20 healthy horses. The effects of indomethacin (INDO) and firocoxib (FIR), on short-circuit current (Isc) in mucosa from the right dorsal colon (RDC) and right ventral colon (RVC) were measured in Ussing chambers by standard electrophysiological techniques. Immunohistochemical methods were used to detect apoptosis (caspase-3) with these NSAIDs and phenylbutazone (PBZ) and to locate the NKCC1 transporter. The Isc in RDC and RVC incubated with INDO or FIR was increased almost 3-fold (P < .0001) by prostaglandin E2 (PGE2) through a system inhibited by loop diuretics (P < .0001). Although these findings and anion replacement studies were consistent with anion secretion, the RDC also displayed an Isc response suggestive of a unique transporter apparently absent in RVC or NSAID-free solutions. In RDC, FIR, INDO, and PBZ induced apoptosis in the lower half of crypts. However, significant differences in apoptotic index were recorded in the RDC between NSAID-treated and control tissues (no NSAID). The effects of NSAIDs on Isc were consistent with reduced anion secretion, which could represent the pharmacological equivalent of the transport failure responsible for Cystic Fibrosis (CF) in other species. Failure of anion secretion could interfere with buffering acid from intraluminal fermentation, which could suggest a treatment target for right dorsal colitis.

Colon resection and anastomosis as treatment of an idiopathic colo‐colic intussusception in an adult horse

SummaryAn 18‐year‐old Thoroughbred gelding was referred for further investigation and treatment of acute colic. Exploratory celiotomy was recommended based on the degree of suspected large colon distension on rectal palpation, and only transient reprieve from colic signs following analgesia. This subsequently revealed an intussusception affecting the left dorsal colon (LDC) with the orad LDC (intussusceptum) within the aborad LDC (intussuscipiens). The intussusception, approximately 20 cm in length, was obstructing the colon. Following exteriorisation, reduction of the intussusception was performed, but marked thickening of the colon wall and luminal obstruction led to the decision to perform a partial colon resection of the left dorsal and ventral colon and side‐to‐side anastomosis. The gelding made an unremarkable recovery from anaesthesia and progressed well post‐operatively. Histopathology found no clear cause of the intussusception. Follow‐up (11 months post‐operatively) confirmed complete recovery and the horse had returned to the previous level of light exercise.

Macleaya cordata extract phytogenic additive: A safe alternative for horses that influences intestinal wall thickness

Macleaya cordata extract (MCE), a phytogenic additive, is used in various species because of its multiple biological effects. These effects are linked especially to its major active compound sanguinarine, an isoquinoline alkaloid. To date, there is little information on its effects on horses. Our objectives were to determine whether a commercial MCE phytogenic additive is safe for horses and evaluate the effects of increasing inclusion rates of it on gut health and systemic inflammation of horses fed with a high-starch diet. The study design was a contemporary double 4 × 4 Latin square design. Eight healthy gelding ponies were used (8 experimental units per treatment, and a total of 32 experimental units). Dry matter intake was 1.75% body weight (BW) and starch intake was 2.2 g/kg BW per meal. Horses were randomly assigned into four treatments: Control, without MCE; S1, 1 mg MCE/kg BW; S1.5, 1.5 mg MCE/kg BW; and S2, 2 mg MCE/kg BW. Feed safety was determined by hemogram, leucogram, serum biochemical, and oxidative stress analyses. Systemic inflammation was measured by fibrinogen and gene expression of interleukins (IL) 6 and 10 in peripheral blood mononuclear cells (PBMC). The thickness of the right dorsal colon (RDC) wall was examined by abdominal ultrasonography as a variable related to gut health. Data were analyzed by PROC MIXED of SAS, and the means were compared using Tukey's test at 5% significance. RDC wall thickness, fibrinogen, IL-6, and IL-10 were analyzed by orthogonal polynomials and Pearson correlation. Serum albumin presented a lower value in S2 (2.97 g/dL) when compared to Control (3.10 g/dL) (P = 0.005), but albumin/globulin relation was not different among treatments. In orthogonal polynomial analyses, there were no differences among the systemic inflammatory variables; only RDC wall thickness values presented a linear response (R² = 0.223; P = 0.001). Pearson correlation showed a strong positive and significant correlation between IL-6 and IL-10 (R = 0.818; P < 0.001). The commercial MCE is safe for horses up to doses of 2 mg/kg. No systemic anti-inflammatory effects were observed, but the thinner intestinal wall in supplemented horses showed that the phytogenic additive had a local effect. We suggest that further studies must be done using this commercial MCE for horses.

Ex vivo evaluation of a novel suture loop method for equine intestinal biopsies.

To compare a novel suture loop method for intestinal biopsies (SLB) with a two-layer, hand-sutured biopsy (HSB) technique in equine small and large intestines. Experimental, randomized, ex vivo study. Eight healthy adult horses. The duodenum, aboral jejunum, and ventral and dorsal large colon were harvested after euthanasia and divided into three sections each. The sections were randomized to SLB, HSB, or control (C, no biopsy) groups. Tissue samples were excised after placement of a suture loop formed by a 4S Roeder knot and oversewn with a Cushing pattern using barbed suture (SLB), or a simple continuous pattern oversewn with a Cushing pattern (HSB). Intraluminal diameter was assessed with contrast radiographs; bursting pressure and wall tension were determined using a solid-state sensor after instillation of fluid. Tissue samples were evaluated by a board-certified pathologist. Tissue samples were full thickness with similar depth and quality (p > .3). Changes in intraluminal diameter did not differ between methods (p > .16). The bursting pressures were higher for controls than biopsied sections (p < .009) but were not different between biopsy methods (p = .998). Bursting wall tension was higher for controls (p < .02) and was similar for both biopsy methods (p = .852). The SLB was equivalent to HSB in strength and effect on intraluminal diameter. The HSB samples were larger and more likely to contain mucosa/villi for histologic diagnosis. The SLB method can be adapted for laparoscopic surgery to obtain both small and large intestinal biopsies. Further investigation is needed before clinical use.

Intestinal hemangiomas in 8 horses.

This retrospective study describes 8 cases of intestinal hemangioma diagnosed in horses during postmortem examination or surgical biopsy at the University of Tennessee College of Veterinary Medicine. In all cases, the intestine was the sole organ affected, and lesions were focal (3/8) or multifocal (5/8). Nodules were most commonly within the small intestine (7/8), particularly the jejunum (5/7). One case was in the left dorsal colon, which is the first report of hemangioma in the large colon of a horse. Lesions were discrete, raised, smooth, black to red, and ranged from 2 to 15 mm in diameter. Microscopically, all lesions were cavernous type and mural, most frequently within the muscularis (6/8). A majority of cases occurred in middle aged to older horses (average age of 19.3 years), and no breed or sex predilections were identified. The hemangiomas were considered incidental findings.

Large intestinal ganglioneuromatosis in a juvenile Arabian filly: Management and long‐term follow‐up

SummaryAn 11‐month‐old Arabian filly was presented for chronic diarrhoea, ill‐thrift and intermittent colic. Abdominal ultrasonography revealed multifocal regions of marked colonic wall thickening. Exploratory laparotomy confirmed multifocal, multi‐sized nodular and segmental intramural mass‐like lesions affecting the right ventral and transverse colon, respectively. Locally extensive regions of mural thickening in the aborad transverse colon resulted in severe luminal restriction (&lt;2.5 cm) and subsequent obstruction of the orad transverse and right dorsal colons with impacted feed material. The lesions were unresectable and full‐thickness biopsy samples were submitted for histopathological evaluation. The filly was subsequently diagnosed with transmural intestinal ganglioneuromatosis of the right ventral and transverse colons. The filly was successfully conservatively managed over a 24‐month follow‐up duration. Management consisted of long‐term dietary modifications in the form of a low‐bulk diet, as well as enteral laxatives and a tapering course of corticosteroids postoperatively. This is the first case of intestinal ganglioneuromatosis in veterinary literature that was (1) diagnosed in a juvenile horse, (2) successfully medically managed and (3) followed up for more than 12 months.

Use of a pneumatic device for intraluminal enterolith fragmentation in horses

SummaryHorses with enterolithiasis may develop clinical signs of colic due to partial or complete obstruction of the right dorsal, transverse or small colon. Laparotomy followed by enterotomy at the site of obstruction or mobilisation of enteroliths to intestinal segments deemed more appropriate for incision is indicated in these cases. However, surgical removal of enteroliths lodged in nonexteriorisable intestinal segments and/or not amenable to mobilisation may be labour intensive and dangerous. Pneumatic impact (or ballistic) lithotripsy is a potential tool for surgical resolution of simple and complex cases of enterolithiasis in horses. This study describes the use of a pneumatic lithotripsy device for intraluminal enterolith fragmentation in five cases of enterolithiasis. Seven calculi were successfully fragmented. In four cases, fragmentation was achieved at the site of obstruction and fragments exteriorised through an enterotomy incision created for device introduction or advanced towards the rectum and removed. In two cases, enteroliths were manipulated back to the pelvic flexure, fragmented and removed. Findings of this study suggest that intraluminal enterolith fragmentation can be used to avoid long enterotomy incisions and facilitate removal of calculi lodged in bowel segments that cannot be exteriorised. However, it is important to be aware of the risks of enterolith fragmentation in nonexternalisable bowel segments that cannot be visualised for intestinal viability assessment.

Colonic T-cell-rich, large B-cell lymphoma associated with equid herpesvirus 5 infection and secondary trans-colonic fistula in a horse.

A 17-y-old Rocky Mountain gelding was presented to the Virginia-Maryland Veterinary Teaching Hospital because of a 4-wk history of anorexia, weight loss, lethargy, and fever of unknown origin. Abdominal ultrasound revealed lymphadenomegaly of the abdominal and colonic lymph nodes, thickening of the wall of the large colon, and a mass associated with the large colon. The horse was euthanized given a poor prognosis. On autopsy, an ~20-cm diameter mass was found within the mesocolon between the right ventral and right dorsal colon. The mass had invaded through the colonic walls and formed a fistula between the 2 involved lumina. On histologic evaluation, the mass consisted of small numbers of large neoplastic lymphocytes, numerous small lymphocytes, and many foamy macrophages. A diagnosis of T-cell-rich, large B-cell lymphoma was made based on immunohistochemical staining for CD79a, CD3, and Iba1; concurrent infection with equid herpesvirus 5 was confirmed with in-situ hybridization (ISH). To our knowledge, neither a trans-colonic fistula resulting from alimentary lymphoma in a horse nor detection of intralesional equid herpesvirus 5 in equine alimentary lymphoma by ISH has been reported previously.

Surgical enlargement of the epiploic foramen in horses.

To assess the safety and efficacy of a method for digitally enlarging the caudal aspect of the epiploic foramen (EF). Healthy horses and clinical cases of EF entrapment (EFE). Fourteen healthy horses and three clinical cases. Through a ventral midline celiotomy under general anesthesia, the EF was enlarged by digital separation of the caudal attachments of the caudate lobe of the liver from right dorsal colon, right kidney, gastropancreatic fold, and pancreas. Healthy horses were euthanized under anesthesia, and the enlarged EF was measured at necropsy. The method used for enlarging the EF did not cause clinically relevant hemorrhage, as determined by visual inspection of the EF in 14 horses at necropsy and by vital parameters under anesthesia in all horses. In clinical cases, EFE was reduced following enlargement of the EF, and no intraoperative complications were encountered. In one clinical case, necropsy at 30 days confirmed partial closure of the enlarged EF. The method proposed enlarged the EF safely and effectively. Limitations of the study include the small number of clinical cases and the lack of postoperative follow-up on the healthy horses. Enlargement of the EF at its caudal extent should be considered in selected cases of EFE in which manual reduction is difficult or protracted. Although the procedure was safe in this study, knowledge of the anatomy, practice on cadavers, and careful selection of cases with greatest need are recommended before clinical use.

Integrated multi-omics reveals novel microbe-host lipid metabolism and immune interactions in the donkey hindgut.

Evidence has shown that gut microbiota play a key role in host metabolism and health; however, little is known about the microbial community in the donkey hindgut as well as the interactions that occur between gut microbes and the host. This study aimed to explore the gut microbiome differences by analyzing the microbial community and differentially expressed genes (DEGs) related to lipid metabolism and the immune system along the donkey hindgut. The hindgut tissues (cecum, ventral colon, and dorsal colon) were separated, and the contents of each section were collected from six male donkeys for multi-omics analysis. There were significant differences in terms of dominant bacteria among the three sections, especially between the cecum and dorsal colon sites. For instance, species belonging to Prevotella and Treponema were most abundant in the cecum, while the Clostridiales_bacterium, Streptococcus_equinus, Ruminococcaceae_bacterium, etc., were more abundant in the dorsal colon. Apart from propionate, the concentrations of acetate, isobutyrate, valerate and isovalerate were all lower in the cecum than in the dorsal colon (p < 0.05). Furthermore, we identified some interesting DEGs related to lipid metabolism (e.g., ME1, MBOAT1, ACOX1, ACOX2 and LIPH) and the immune system (e.g., MUC3B, mucin-2-like, IL17RC, IL1R2, IL33, C1QA, and MMP9) between the cecum and dorsal colon and found that the PPAR pathway was mainly enriched in the cecum. Finally, we found a complex relationship between the gut microbiome and gene expression, especially with respect to the immune system, and combined with protein-protein interaction (PPI) data, suggesting that the PPAR pathway might be responsible, at least in part, for the role of the hindgut microbiota in the donkeys' gut homeostasis. Our data provide an in-depth understanding of the interaction between the microbiota and function in the healthy equine hindgut and may also provide guidance for improving animal performance metrics (such as product quality) and equine welfare.

Caecocolic ligament hypoplasia in a Thoroughbred filly with volvulus of the large colon

SummaryAn 11‐month‐old Thoroughbred filly was referred to the hospital with signs of severe abdominal pain unresponsive to medical treatment. Upon arrival, the filly had a heart rate of 60 beats/min, pink mucous membranes and continued to show severe colic signs despite sedation. Due to the severity of colic signs, general anaesthesia was induced immediately. Exploratory celiotomy revealed a large colon volvulus of more than 360 degrees and hypoplasia of the caecocolic ligament between the caecum and right dorsal colon. The large colon volvulus was corrected, and the filly recovered uneventfully from general anaesthesia. Post‐operative treatment included intravenous fluids and intravenous lidocaine continuous rate infusion, parenteral nutrition, systemic antibiotics, nonsteroidal anti‐inflammatories, gastroprotectants and restricted feeding. The filly experienced several post‐operative complications associated with severe enterocolitis including pyrexia, leukopenia and diarrhoea but made a full recovery and was discharged to the farm after 16 days of hospitalisation. Long‐term follow‐up was available for 22 months after surgery without further reports of colic and the filly had entered race training. Hypoplasia of the caecocolic ligament in association with colic in horses has rarely been reported in the equine literature. To date, only two further case reports of young horses with large colon volvulus and hypoplasia of the caecocolic ligament have been published. In contrast to the presenting case, several other mesenteric abnormalities were present in these two cases in addition to the hypoplastic caecocolic ligament and both horses were eventually euthanised. The pathogenesis of hypoplasia of the caecocolic ligament remains unclear but may include the disruption of early stages of embryogenesis. An abnormal caecocolic ligament has been suggested to potentially predispose horses to large colon volvulus. The presenting case indicates that as an isolated abnormality, a hypoplastic caecocolic ligament may not result in reduced long‐term survival in horses with large colon volvulus.

Gut health of horses: effects of high fibre vs high starch diet on histological and morphometrical parameters

BackgroundThe conventional feeding management of horses is still characterized by high starch and low fibre diets, which can negatively affect horse’s gastrointestinal health. Thus, the aim of this study was to compare the effects of a high-starch (HS) vs. a high-fibre (HF) diet on gut health in horses. A total of 19 Bardigiano horses destined for slaughter and aged 14.3 ± 0.7 months were randomly allotted to two dietary groups: HS (5 fillies and 4 colts,) and HF group (7 fillies and 3 colts). They received the same first-cut meadow hay but different complementary feeds for 72 days: HS group was fed 8 kg/animal/day of a starch-rich complementary feed while HF group was fed 3.5 kg/animal/day of a fibre‐rich complementary feed. At slaughter, stomachs were separated and washed for the evaluation of the glandular and squamous regions. Also, duodenum, jejunum, ileum, apex of the caecum, sternal flexure, pelvic flexure, right dorsal colon, rectum and liver were excised and submitted to histomorphometrical evaluation.ResultsThe glandular region of HS group presented more severe gastric mucosa lesions compared to the HF group (P = 0.006). Moreover, a statistical tendency (P = 0.060) was found for the squamous region, presenting a higher score in HS than HF diet. Regarding morphometry, in jejunum villus height to crypt depth (Cd) ratio was influenced by sex, being greater in males than in females (P = 0.037) while in ileum Cd depended on interaction between sex and diet, being greater in males of HS group (P = 0.029). Moreover, in the duodenum and right dorsal colon the severity of the inflammation depended on sex (P = 0.024 and 0.050), being greater in females than in males. On the contrary, in the jejunum and in the pelvic flexure, inflammation was influenced by diet, being more severe in HS than in HF group (P = 0.024 and 0.052).ConclusionsThese results suggested that HS diet provoked more severe mucosa lesions in the glandular region of the stomach and a higher inflammation both in the jejunum and pelvic flexure. The present study can represent a starting point for further investigations on gut health in horses.

Comparison of the host response to larvicidal and nonlarvicidal treatment of naturally acquired cyathostomin infections in horses.

This study aimed to collect information on local and systemic inflammatory responses, and goblet cell-associated components, following anthelmintic treatment with moxidectin and ivermectin in horses naturally infected with cyathostomin parasites. Thirty-six horses aged 2-5 years of age were randomly allocated to three groups. Group 1 received ivermectin/praziquantel (0.2mg/kg), Group 2 received moxidectin/praziquantel (0.4mg/kg) and Group 3 were untreated controls. Tissue samples from the Cecum, Dorsal and Ventral Colons were used for histopathological evaluation and preserved for RNA isolation and gene expression analysis. Whole blood was collected weekly for gene expression analysis as well. The control group had significantly higher inflammation associated with higher larval scores. The treatment groups displayed no differences in larval counts and inflammatory cell populations (p > .05). Mucosal larval counts were positively correlated with goblet cell hyperplasia scores (p=.047). The moxidectin-treated group had a significantly lower expression of IFN-γ (p < .05). The data suggest that removal of cyathostomins reduced the pro-inflammatory response associated with cyathostomin infections. Pro-inflammatory reactions associated with anthelmintic treatment were minimal, but lowest for moxidectin-treated horses. Results suggested that cecum, ventral and dorsal colons responded differently to cyathostomin larvae, which may have implications in the disease process.

Mechanisms of bicarbonate secretion in the equine colon ex vivo.

To examine bicarbonate (HCO3-) secretion ex vivo in the equine large colon to determine any differences between the right dorsal colon (RDC) and right ventral colon (RVC). The effect of phenylbutazone (PBZ) on HCO3- secretion was examined in the RDC. 14 healthy horses. In anesthetized horses (n = 10), segments of mucosa from RDC and RVC were harvested to measure HCO3- secretion ex vivo with the pH Stat method. The effect of PBZ on HCO3- secretion in the RDC was studied in 4 additional horses. Three distinct mechanisms of HCO3- secretion previously described in a murine model were confirmed in the equine colon. The RDC had a greater capacity for electrogenic, Cl--independent HCO3- secretion than the RVC (P = 0.04). In the RDC, all HCO3- secretion was decreased by PBZ (P < 0.02) but was not studied in the RVC because of low baseline secretion. Secretion of HCO3- by the RDC could play a pivotal role in equine colon physiology, because intense microbial fermentation in this site could require HCO3- secretion to buffer short-chain fatty acids. Inhibition of this secretion by PBZ could interfere with mucosal buffering and predispose to changes associated with right dorsal colitis.

Precision of cyathostomin luminal worm counts: Investigation of storage duration and fixative

Essentially all grazing horses are infected with cyathostomin parasites. Adult cyathostomins reside in the large intestine of the horse and larval stages encyst within intestinal mucosa. Manual worm collection from aliquots of intestinal content is the current gold standard for retrieval and enumeration of luminal parasites, however, no research has been conducted to standardize specific parameters for processing and storage of samples. The aims of this study were (1) to evaluate the precision of current standard operating procedures for enumeration of luminal adult cyathostomin populations, (2) investigate the influence of chosen fixative, either 70 % ethanol or 10 % buffered formalin, as well as storage duration, immediately post necropsy vs. stored for eight weeks, on the magnitude and precision of worm counts, and (3) compare the luminal count magnitude between the three intestinal segments (cecum, ventral colon, dorsal colon). Ten miniature horses were enrolled in this study for euthanasia and necropsy over a four-week period. Luminal worm counts were conducted for 2 % aliquots of the cecum, ventral colon, and dorsal colon and samples were allocated to the two fixatives and the two storage durations. Precision was evaluated by coefficient of variation (CV) and was 13.04 % for total cyathostomin counts. Mean CV for large intestinal segments ranged from 15.31 % to 52.50 % irrespective of fixative used or storage duration. cecum worm counts were significantly lower compared to the ventral colon (p = 0.008) and dorsal colon (p = 0.01). Fixative and storage duration were not statistically associated with count precision or magnitude. This study demonstrated moderate to high precision estimates for luminal cyathostomin worm counts but did not identify any effects of fixative and storage duration within the framework of the study. This is the first study to determine cyathostomin worm count precision, and results will be useful for power analyses in the future.