CHAPTER 192 Examination of the Foal with Colic
Unfortunately, horses can be affected by colic from the first day of life until the last. Evaluation and treatment of acute abdominal pain in foals is somewhat different from that in adult horses because of their size, pain tolerance, and the types of diseases foals acquire. The purpose of this chapter is to attempt to differentiate the medically manageable foal with colic from the foal requiring surgery. This discrimination is especially important in foals because of their predisposition for adhesion formation following abdominal surgery. The decision to treat medically or surgically is resolved by synthesizing information concerning the foal’s history, results of diagnostic tests, and, most important, the physical examination.
In all cases information about the length of the colic episode, degree and progression of pain, passage of feces and urine, consistency of feces, nursing or appetite, and medications received is important. If the foal has had previous health problems and received nonsteroidal anti-inflammatory drugs (NSAIDs), gastric or duodenal ulceration should be suspected. Abdominal abscesses can form in older foals with a history of Streptococcus spp. or Rhodococcus equi pneumonia. If older foals have received anthelmintic medication within 7 to 10 days of the colic episode, ascarid impaction of the small intestine might be causing the clinical signs. Information about the periparturient events may be important when evaluating neonatal foals. Foals with peripartum asphyxia syndrome are at risk for developing paralytic ileus. Premature foals or foals resulting from dystocia are at risk for developing necrotizing enterocolitis. Certainly if the foal has had previous abdominal surgery, abdominal adhesions could be the cause of the current colic episode.
Subjective evaluation of the foal is also important. Although foals appear to be less tolerant of abdominal pain and develop more severe signs of abdominal pain with less severe lesions, such as enteritis, assessing the degree and progression of pain and the response to analgesic medication will help determine therapeutic plans and surgical decision making. Signs of severe pain include rolling and thrashing. More moderate signs of pain include pawing, restlessness, lying down, and abnormal postures. Abnormal postures include standing with the head down and limbs collected beneath the abdomen, which is seen in depressed foals with mild abdominal pain. Foals that strain to defecate tend to adopt a dorsiflexed stance with the hind limbs beneath the abdomen. When foals are straining to urinate, their posture is more ventroflexed with the hind limbs stretched out behind them. Foals with gastric ulceration may roll on to their back, exhibiting bruxism and sialorrhea, especially after nursing. The frequency and intensity with which the foal nurses are important, and the sucking foal should be differentiated from a foal just standing beneath the mare without actually nursing.
After the foal’s behavior is assessed, the foal should be lightly restrained for the physical examination. Hydration and perfusion should be assessed in all foals with signs of colic. Signs of poor perfusion include a capillary refill time longer than 2 seconds; cold ears, muzzle, and extremities; high heart rate; low pulse pressure; decreased or absent urination; and depressed mentation. Increased tenting of the skin on the neck, sunken eyes, and dry, tacky (sticky) mucous membranes are signs of dehydration. Foal urine should be hyposthenuric (specific gravity less than 1.010); urine specific gravity greater than 1.020 may be a sign of dehydration or hypovolemia. Fever above 102° F (39° C) may indicate an infectious cause of the colic episode, such as bacterial or viral enteritis or enterocolitis. Hypothermia is rare but may indicate poor perfusion and is a sign of hypovolemic or hypodynamic shock. A foal can be warmed by improving perfusion with administration of intravenous (IV) fluids, keeping the foal dry and wrapped in towels and blankets, using hot water pads or hot water bottles, and blowing warm air through the blankets, which can be done using a patient warming system (Bair Hugger, model 500, Augustine Medical, Inc.).
Thoracic auscultation should be performed on the right and left sides of the thorax to evaluate the heart and lungs. Mean heart rate is 100 beats per minute during the first 30 days of life and decreases to 60 to 70 beats per minute by age 2 to 3 months. A high heart rate may be a response to pain, excitement, hypovolemia, or endotoxemia. Bradycardia is rare but may be detected in foals with uroabdomen if they are hyperkalemic ([K+] greater than 5.5 mEq/dL). These foals are also prone to developing cardiac arrhythmias. Cardiac murmurs may be normal in foals up to 3 to 5 days old and are usually caused by blood flow through a patent ductus arteriosus. Such murmurs may sound like continuous machinery–type or systolic murmurs. Innocent flow murmurs can be heard in some foals, but these are restricted to the left heart base and are usually less than grade 2/6. Fever and anemia can also result in cardiac murmurs. The lungs should be ausculted on the right and left sides and over the trachea. Borborygmus heard within the thorax is normal because of the shape of the diaphragm and is not indicative of diaphragmatic hernia.
The abdomen can be ausculted, balloted, palpated, and percussed. Progressive borborygmus is produced by gas and fluid interfaces within the gastrointestinal tract. The presence of audible borborygmus is usually considered normal. However, foals with gastrointestinal obstruction will initially have borborygmus that may be increased followed by a period of decreased to absent intestinal sounds, indicating decreased gastrointestinal motility or ileus. Increased borborygmus may indicate enteritis. Percussing the abdomen and listening for a ping can detect gas distension of the cecum and colon. Palpation of the umbilicus and inguinal area is performed to identify hernias. Many reducible umbilical and inguinal hernias are found incidentally during the physical examination, but if pain is elicited during palpation or if the hernia is not reducible, surgery is usually indicated. In cases of inguinal hernia, emergency surgical correction is advised if the tunic is ruptured, small intestine is in the subcutaneous space, and there is medial thigh and preputial edema (Figure 192-1).
Differential diagnoses for neonatal foal colic include meconium retention (see Chapter 187, Meconium Impaction), enterocolitis (see Chapter 191, Inflammatory Bowel Diseases in Foals), uroabdomen and ruptured bladder, and congenital lesions.
Congenital atresia of the colon, rectum, or anus is rare, and reportedly only 12 cases of intestinal atresia occur for every 10,000 horses examined. Colonic atresia occurs twice as frequently as rectal or anal atresia in horses. Foals with colonic atresia pass no meconium, and there is no meconium staining, which differentiates them from foals that are colicky from impaction but have passed some meconium. Foals with colonic atresia develop abdominal distension and signs of abdominal pain between 12 and 24 hours of age. Surgical intervention can be successful in some cases of gastrointestinal atresia, but these foals should be evaluated for other congenital abnormalities, such as rectovaginal fistulas in fillies, rectourethral fistulas in colts, anomalies of the sacral and coccygeal vertebrae, and renal hypoplasia. American Paint Horse foals born with a white coat from an overo-overo mating are at risk for ileocolonic aganglionosis or lethal white syndrome. These foals appear normal at birth but have signs of abdominal pain and distension by 24 hours of age. As with cases of atresia, these foals pass no meconium, and there is no fecal staining on thermometers or enema tubes. There is no treatment for lethal white syndrome because the myenteric ganglia are absent from the ileum, cecum, or colon.
Foals with ruptured bladder or urachal tear usually begin to develop clinical signs of uroabdomen by 24 to 72 hours of age. These foals “flag” their tails, are restless, and strain to urinate. Although most affected foals dribble urine, some may continue to pass a stream of urine. Foals with previous or ongoing septic umbilical structures are at risk for necrosis of the urachus, which can lead to uroabdomen. Foals with uroabdomen caused by a ruptured or torn ureter may show clinical signs later, from 4 to 7 days of age. There is no sex predilection, but these foals may have some history of trauma at birth, such as falling if parturition occurred with the mare standing. Uroabdomen is diagnosed based on ultrasonographic observation of anechoic free peritoneal fluid (Figure 192-2