Gastrointestinal: Colic
Colic in horses encompasses various conditions manifesting as abdominal pain, necessitating a thorough understanding of equine gastrointestinal (GI) anatomy, physiological mechanisms, and diagnostic strategies for veterinary professionals. While colloquially associated with equine abdominal pain, colic represents a spectrum of ailments with diverse etiologies and severity levels.
Gastrointestinal Anatomy: A myriad of clinical signs is associated with colic. Common indicators include repetitive pawing with a front foot, flank region scrutiny, lip curling, neck arching, rear leg raising or abdominal kicking, lying down, side-to-side rolling, sweating, urination posture, straining to defecate, abdominal distention, reduced appetite, depression, and diminished bowel movements. However, it's uncommon for a colicky horse to exhibit all these signs simultaneously. While these signs reliably signal abdominal pain, they don't pinpoint the specific GI tract segment involved or indicate the necessity for surgery.
Diagnosis:
Clinical Evaluation
Clinicopathologic Tests
A definitive diagnosis and appropriate treatment initiation hinge upon thorough patient examination, review of the horse's medical history, identification of the implicated GI tract segment, and determination of the causative factor behind the colic episode. In most cases, colic arises from one of four primary reasons:
Excessive stretching of the intestinal wall by gas, fluid, or ingesta triggers pain impulses via stretch-sensitive nerve endings within the intestinal wall.
Pain ensues due to excessive tension on the mesentery, as in cases of intestinal displacement.
Ischemia occurs, typically due to incarceration or severe intestinal twisting.
Inflammation arises, affecting either the entire intestinal wall (enteritis or colitis) or the intestinal covering (peritonitis), with proinflammatory mediators in the intestinal wall lowering the pain threshold.
The spectrum of conditions causing colic is extensive, thus warranting an initial focus on determining the most likely disease type and commencing appropriate treatments. Subsequently, endeavors should be directed toward achieving a more precise diagnosis, if feasible.
Types of Diseases Causing Colic:
Excessive gas in the intestinal lumen (flatulent colic)
Simple obstruction of the intestinal lumen (impaction)
Obstruction of both the intestinal lumen and blood supply (strangulating obstruction)
Interruption of blood supply to the intestine alone (nonstrangulating infarction)
Intestinal inflammation (enteritis or colitis)
Abdominal cavity lining inflammation (peritonitis)
Intestinal lining erosion (ulceration)
"Unexplained colic"
Generally, horses with strangulating and complete obstructions necessitate emergency abdominal surgery, while those with other disease types can receive medical treatment.
Consideration of the present colic episode and past occurrences, if any, aids in determining if the horse has experienced recurring issues, the duration and severity of the current episode, fecal passage status, and treatment response. Additionally, assessing the horse's deworming and dental care history, dietary changes, cribbing behavior, and activity level during the onset of the colic episode provides crucial insights.
A comprehensive physical examination encompasses evaluation of the cardiopulmonary and gastrointestinal systems. The oral mucous membrane condition, heart rate, respiratory rate, response to nasogastric tube insertion, abdominal palpation, rectal examination findings, and peritoneal fluid analysis all contribute to the diagnostic process. Ultrasonographic assessment aids in differentiating between medically manageable conditions and those necessitating surgical intervention, providing invaluable insights into the underlying pathology.
Medical Treatment
Horses experiencing colic may require either medical or surgical interventions. While almost all cases necessitate some form of medical intervention, surgery is reserved for specific types of intestinal conditions. The choice of medical treatment is guided by the underlying cause of colic and the severity of the condition. In certain cases, initial medical treatment may be administered, followed by evaluation of the horse's response, especially if the pain is mild and the cardiovascular function appears normal. Ultrasonography serves as a valuable tool to assess the effectiveness of nonsurgical treatment. Surgery may be employed for both diagnostic and therapeutic purposes if required.
If a rectal examination reveals evidence of intestinal obstruction with dry ingesta, the primary goal of treatment is to rehydrate and evacuate the intestinal contents. In cases where the horse exhibits severe pain and signs of fluid loss (elevated heart rate, prolonged capillary refill time, and mucous membrane discoloration), initial treatment aims to alleviate pain, restore tissue perfusion, and address any abnormalities in blood and body fluid composition. Suspected damage to the intestinal wall necessitates measures to mitigate the effects of bacterial endotoxins that may permeate the damaged barrier. Additionally, if parasitic involvement is suspected, treatment aims to eradicate the parasites.
Pain Relief In most cases of colic, mild pain can be managed effectively with analgesics. However, caution is warranted when administering analgesics, as stronger medications may mask clinical signs crucial for diagnosis, particularly in cases of intestinal twist or displacement. Therefore, a thorough physical examination should precede any medication administration. Nevertheless, in situations of severe colic where the horse poses a risk to itself or others, analgesics may need to be administered promptly. Selecting an analgesic with minimal adverse effects and minimal alteration of the horse’s behavior is essential.
Commonly used medications for abdominal pain include NSAIDs, which inhibit prostaglandin production. When used appropriately, NSAIDs rarely exhibit toxic effects on the kidneys and GI tract. However, it's important to note that flunixin meglumine may obscure early signs of conditions requiring surgery and should be used cautiously in horses with colic. Hyoscine butylbromide, a mild analgesic and antispasmodic, may benefit horses with mild colic symptoms.
Sedation is often necessary for managing pain in colic cases, with xylazine being a commonly used agent. Although effective, xylazine has short-lived effects and may inhibit intestinal muscle activity, necessitating careful use. Detomidine, a more potent and longer-acting sedative, is an alternative option. Butorphanol, an opioid analgesic, is frequently used for pain management in colic cases, with few adverse effects on the GI tract or heart. However, caution should be exercised with opioid administration to prevent excitement and instability.
In addition to analgesics, certain procedures such as nasogastric tube placement can alleviate pain by relieving gastric distention, thereby preventing gastric rupture.
Fluid Therapy Fluid therapy plays a crucial role in managing colic by preventing dehydration and maintaining vital organ perfusion. The administration route depends on the specific intestinal condition. Horses with conditions like strangulating obstruction or enteritis often require intravenous fluids due to impaired fluid absorption from the diseased intestine. Intravenous fluids help counteract circulatory shock resulting from abnormal fluid accumulation in the intestine.
Intravenous fluid selection is guided by laboratory tests assessing hemoconcentration, acidosis, and electrolyte imbalances. Sterile replacement fluids, resembling blood electrolyte concentrations, are typically administered to mildly to moderately affected horses. Severe cases of circulatory shock may necessitate rapid infusion of large volumes of IV fluids, with hypertonic saline used in some instances to rapidly increase plasma volume. Continuous monitoring and adjustment of fluid therapy are vital until the horse’s intestinal function normalizes, electrolyte balance is restored, and the horse can maintain its fluid requirements orally.
Nasogastric tube administration of fluids may be considered for colonic impactions, although intravenous fluids are preferred in most cases. However, fluids or medications should not be administered via the nasogastric tube if fluid reflux is observed, indicating inadequate emptying of the stomach or small intestine.
Protection Against Enteric Bacteria Components Disruption of the mucosal barrier in the GI tract can lead to absorption of bacterial components into the bloodstream, triggering systemic inflammatory responses. Preventing or minimizing these responses is crucial in colic treatment. NSAIDs like flunixin meglumine can mitigate early inflammatory effects by reducing prostaglandin production. Administered at lower dosages, flunixin can offer protection against endotoxemia without masking surgical indications.
Neutralizing antibodies against endotoxin and polymyxin B, which prevent endotoxin interaction with inflammatory cells, are potential therapeutic strategies. Although their efficacy remains debated, early administration is recommended to mitigate inflammatory responses.
Intestinal Lubricants and Laxatives Simple obstruction of the large colon by dehydrated ingesta is a common cause of colic in horses. Lubricants or fecal-softening agents can help soften impacted ingesta, facilitating their passage. Mineral oil is commonly used for large-colon impactions, coating the intestine and aiding ingesta movement. Dioctyl sodium sulfosuccinate (DSS) and psyllium hydrophilic mucilloid are alternative agents, with DSS more effective in softening impactions but requiring cautious use due to potential colitis risk.
Strong laxatives that stimulate intestinal contractions are generally avoided, as they may exacerbate the problem. Fluid therapy, alongside lubricants or laxatives, forms an integral part of colic management.
Larvicidal Deworming Parasitic infestations, particularly by large bloodworms like Strongylus vulgaris, have been associated with colic in horses. Modern deworming medications like ivermectin and moxidectin offer larvicidal activity against migrating larvae, reducing the incidence of colic due to parasitic infestations. Additionally, fenbendazole may be used to target migrating strongyles. Larvicidal deworming is essential for managing cyathostomiasis, a condition characterized by colic, diarrhea, backing up sand impactions. Proper deworming protocols are critical in preventing parasitic-induced colic.
Surgical treatment:
Surgical intervention is warranted when mechanical obstruction or compromised intestinal blood supply cannot be resolved medically. Emergency abdominal surgery is often necessary for horses with severe abdominal pain and signs indicative of strangulating obstruction or severe displacement. Prompt surgical correction is crucial for improving survival rates. Indications for surgery include uncontrollable pain, significant fluid reflux, absence of intestinal sounds, abnormal peritoneal fluid, and identifiable lesions on rectal examination.
Early surgical intervention improves prognosis, with procedures involving repositioning, obstruction removal, or intestinal resection based on the specific pathology. Postoperative care may include antimicrobial therapy, fluid support, and analgesia to mitigate complications and aid recovery.
Prognosis Survival rates for horses undergoing emergency abdominal surgery have improved significantly, with recent studies reporting rates exceeding 80%. Prognostic indicators such as pain severity, intestinal distention, mucous membrane color, and cardiovascular function help predict outcomes. Overall, prompt diagnosis, appropriate treatment, and diligent postoperative care are critical for ensuring favorable outcomes in horses with colic.
Surgery Surgical intervention is warranted when mechanical obstruction or compromised intestinal blood supply cannot be resolved medically. Emergency abdominal surgery is often necessary for horses with severe abdominal pain and signs indicative of strangulating obstruction or severe displacement. Prompt surgical correction is crucial for improving survival rates. Indications for surgery include uncontrollable pain, significant fluid reflux, absence of intestinal sounds, abnormal peritoneal fluid, and identifiable lesions on rectal examination.
Early surgical intervention improves prognosis, with procedures involving repositioning, obstruction removal, or intestinal resection based on the specific pathology. Postoperative care may include antimicrobial therapy, fluid support, and analgesia to mitigate complications and aid recovery.
Prognosis Survival rates for horses undergoing emergency abdominal surgery have improved significantly, with recent studies reporting rates exceeding 80%. Prognostic indicators such as pain severity, intestinal distention, mucous membrane color, and cardiovascular function help predict outcomes. Overall, prompt diagnosis, appropriate treatment, and diligent postoperative care are critical for ensuring favorable outcomes in horses with colic.
Reference: Veterinary Medicine (Large Animal) by Constable
