Meconium is the earliest feces of newborn foals. It is composed of intestinal secretions, swallowed amniotic fluid, and cellular debris; it has a sticky, caramelized appearance. Most foals pass their meconium within the first 9–12 hr of life. If sufficient quantities of meconium are not evacuated, meconium impaction can lead to clinical signs of colonic obstruction, which usually manifest in the first 12–96 hr. These signs may include abdominal pain (colic), tachypnea and tachycardia, tail “swishing,” restlessness, straining to defecate, and abdominal (gas) distention. Published reports suggest that meconium impaction may be more likely in foals born after >340 days of gestation and in colts. Meconium can usually be identified either by plain or contrast abdominal radiography or ultrasonography, or by careful digital rectal examination with adequate restraint or sedation. On radiographs, meconium often appears as granular contents in the ascending or descending colon, with fluid- or gas-distended intestine proximal to the obstruction.
Many cases of meconium impaction respond to medical therapy, including judicious use of analgesics, IV fluid therapy, oral laxatives (4–8 oz mineral oil administered via a nasogastric tube; 1–2 oz milk of magnesia), and enemas as the mainstay of therapy. Warm-water liquid detergent (eg, Palmolive®) enemas (½ teaspoon liquid detergent added to 500 mL water) are preferred, although commercial phosphate (Fleet®) enemas can also be used (repeated administration may increase risk of phosphate toxicity). Acetylcysteine retention enemas may also be highly effective, because acetylcysteine is hypothesized to cleave disulfide bonds in the mucoprotein molecules of meconium, which decreases its overall tenacity. A 4% acetylcysteine solution is made by adding 20 g of baking soda and 8 g of acetylcysteine to 200 mL of water. A 30-french Foley catheter with a 30-mL balloon is inserted ~2.5–5 cm into the rectum, and the balloon is slowly inflated to occlude the rectum. Subsequently, 100–200 mL of the 4% acetylcysteine solution is administered by gravity flow and retained for 30–45 min. If needed, treatment can be repeated in 12 hr. Occasionally, repeated enemas can result in significant mucosal irritation and persistent straining beyond the resolution of the meconium impaction, thereby confounding the assessment of treatment success.
Surgical intervention should be considered if medical therapy is unsuccessful, especially in the face of persistent pain unresponsive to analgesics, persistent tachycardia, progressive abdominal enlargement, or increased peritoneal fluid protein and/or nucleated cell count.
The prognosis of uncomplicated meconium impaction is generally considered good to excellent.