Meconium Impaction - Horse

Also known as:

Meconium Retention Colic in foals Impaction Simple Obstruction Large Intestinal Simple Obstruction Small Colon Impaction Descending Colon Impaction

Description

Meconium impaction or retention is the most common cause of colic in the first 24 hours of life. Meconium is mucilaginous material in the intestine of the term fetus containing a mixture of cellular debris, secretions of the intestinal glands, bile and amniotic fluid. Meconium usually begins to be evacuated from the newborn foal within 3 h after birth, and is considered retained if the foal makes frequent attempts but fails to produce meconium by age 12 h.(Pusterla)

Signalment

Newborn foals. More common in colts than fillies, particularly if they are overdue. This may be related to a narrower pelvic inlet. This condition is the most common cause of rectal obstruction in foals (White and Lessard 1986). Male foals appear to be more commonly affected than fillies due to the smaller pelvic inlet in the colt (Martens 1982).(Pusterla)

Aetiology

Meconium is composed of glandular secretions, swallowed amniotic fluid and cellular debris. It is dark brown to black and cement- or pellet-like in texture. Most foals defaecate shortly after their first meal, within 24 hours of birth. Once meconium has been passed, the faeces become a dark yellow, reflecting milk digestion. Meconium retention may result from a lack of colostrum ingestion, since colostrum is a natural laxative. Thus foals with meconium retention should also be checked for failure of passive transfer (FPT). Intestinal dysmotility may also be an indication of perinatal asphyxia. Other factors predisposing to meconium retention include maternal malnutrition, delayed colostral intake with loss of its laxative effect, conditions that compromise the foal, such as asphyxiation, dystocia, prematurity, low birth weight, intestinal disease or hypomotility of the colon, and dehydration (Semrad and Shaftoe 1992).(Pusterla)

Clinical Signs

• Colic (due to gas accumulation within the bowel)
• Continuous straining
• Classic 'arched back' stance
• Foal depressed or remains bright
• Normal or reduced level of suckling
• Tail swishing and elevation
• Restlessness

Early signs of failure to pass meconium may include restlessness, tail swishing, frequent posturing to defaecate, tail elevation and disinterest in sucking (Madigan 1994). Advanced cases may be presented with abdominal distention and other clinical signs of colic. Most impactions are located in the small colon at the pelvic inlet, but can also be located in the dorsal or transverse colon.(Pusterla)

Diagnosis

• CAREFUL digital examination per rectum (for diagnosis only)
• Abdominal palpation (meconium may be palpable if abdominal tympany is not too advanced)
• Abdominal ultrasound
• Abdominal radiography

Diagnosis is based on clinical signs and detection of a firm mass upon digital rectal, lack of passage of milk stool and abdominal palpation or radiography of faecal masses in the colon (Edwards 1997).(Pusterla)

Differential Diagnoses

• Uroperitoneum: the foal may assume a more extended stance (NB: a ruptured bladder may occur simultaneously with meconium retention)
• Gastrodudodenal ulceration
• Impending enteritis
• Obstructive gastrointestinal lesions
  • Small intestinal intussusception
  • Torsion
  • Atresia coli

Treatment

• Enema: warm soapy water made with a mild soap that can be administered through soft rubber tubing by gravity.
• Liquid praffin: 300ml by nasogastric tube for foals that do not respond rapidly to an enema
• Muzzling and maintenance rate fluids IV: for persistent meconium retention resulting in significant abdominal distension. A constant rate infusion of 5-10% dextrose will provide some calories in addition to the free water needs. Dextrose should NOT be given as a bolus.
• Retention enema: a more aggressive treatment may be required using acetylcysteine which is an irritant and increases secretion. 20g baking soda and 8g acetylcysteine are added to 200ml water to create a 4% acetylcysteine solution of pH7.6. A 30-french Foley catheter is inserted 2.5 to 5cm into the rectum and the bulb slowly inflated to occlude the rectum. 100-200ml of the solution is adminstered under gravity and retained for 30-45mins by occluding the catheter.
• Surgery: may be required for extreme cases
• Analgesia: may be needed for some foals. NSAIDs have deleterious effects on renal function and gastric mucosal blood flow, so they should be avoided if possible. Butorphanol given IM at 0.05 to 0.1mg/kg may help to prevent straining. Hyoscine (Buscopan-Boehringer) may alleviate the colic.
• Intranasal oxygen: is useful for foals with significant abdominal distension.

Prognosis

Most cases resolve with medical management within 12-24hrs.

Complications

Foals with meconium retention may be at risk of sepsis because bacterial translocation may occur across the disrupted intestinal mucosa. Blood cultures are thus advisable and foals should be monitored closely for clinical signs of sepsis. Continuous straining may lead to patent urachus.

References

Wilkins, P.A (2010) 'Diseases Of The Gastrointestinal Tract' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) Equine Internal Medicine (Third Edition), Saunders, Chapter 21.