|Issue 5: Neonatal Diseases
Foals are not able to produce antibodies until about 2 weeks of age. They receive their first antibodies or immunoglobulins (Ig) from the mother via the ingestion of colostrum. This is the thick, sticky, yellowish substance that the mares udder produces for the first 24 hours of the foals life. The foals GI tract is specially designed to absorb large substances during the first day of life, so anything present in the GI tract of appropriate size will be absorbed. As the foal absorbs Ig, the GI tract gradually closes. Only 20% of the absorptive capacity remains after 12 hours. Consequently, if the foal does not nurse well during the first 12 hours of life, he or she may not get all the antibody needed to fight off infection. This condition is called Failure of Passive Transfer (FPT). Some mares produce colostrum that is low in immunoglobulin - this can also lead to FPT, even when the foal nurses well. Obviously, FPT leaves the foal at greater risk for infection. However, we now know that other factors are involved.
Since the foals GI tract absorbs large particles without regard to their makeup, bacteria can also be absorbed. Exposure to large numbers of pathogens or to extremely virulent organisms can dramatically increase chance of infection. Therefore, foaling on very clean premises, washing the mares udder and hindquarters before and after birth, and dipping the navel the first 2 days of life is also important.
Uroperitoneum is defined as the presence of urine in the abdominal cavity. This develops as a result of damage to the internal structures of the urinary tract - the bladder, kidneys, urethra, ureters, and/or the urachus. Problems involving damage to the kidneys or ureters is rare but can be seen in adults with uroliths (kidney stones). Urethral problems are also rare. However, rupture of the bladder is not uncommon in 3-5 day-old foals. Damage to the bladder is believed to develop during parturition. Depending on the size of the hole in the bladder, foals may still urinate normally. As the abdomen fills with urine, the foal becomes uncomfortable and may strain. He or she may also become depressed and not nurse well. If the abdomen gets very full, lung expansion is compromised and the foals respiratory effort may increase.
The presence of urine in the abdomen also leads to systemic problems as it causes alteration of electrolyte levels in the blood. Urine is high in potassium (K+) and low in sodium (Na+), whereas the blood content is opposite. Because the lining of the abdomen is permeable to electrolytes, sodium and potassium are exchanged across this membrane in response to the concentration gradient - towards the blood for K+, away from the blood for Na+. Blood K+ levels can be high enough to cause cardiac arrhythmias in some cases. The decreased blood Na+ level affects hydration also as water always follows sodium. The "effective circulating volume" of the blood will decrease with the loss of sodium and fluid into the abdomen.
A suspicion of uroperitoneum is often conveyed by the history and levels of electrolytes and creatinine measured in blood and abdominal fluid. However, this will not reveal information as to where within the urinary tract damage has occurred. Dye studies can be performed to confirm the presence of urine in the abdomen and sometimes localize a lesion. Fluorescein dye can be instilled into the bladder via the urethra. A sample of abdominal fluid is then obtained. If the fluid is orange, the dye has leaked into the abdominal cavity and confirms bladder rupture. Use of contrast media made with iodine based products will show leakage on radiographs of the abdomen. Currently, however, diagnosis of uroperitoneum is most commonly determined via ultrasound of the abdomen. A tear in the bladder can usually be visualized on a sonogram.
Initial treatment for uroperitoneum involves drainage of the urine from the abdomen coupled with simultaneous IV fluid therapy. This is performed to decrease K+ levels and improve hydration. Fluids without potassium must be used. Glucose and insulin may also be given to decrease the level of K+ in the blood. Once the patient is stabilized, surgery can be performed if needed. Small holes in the bladder may heal on their own with time with repeated or continuous peritoneal drainage. Large tears must be repaired surgically. If potassium and fluid levels are carefully managed, anesthesia and surgery are usually completed uneventfully. Prognosis following surgery is excellent for most foals.
Damage to the urachus can also lead to uroperitoneum. The urachus is a structure within the umbilical cord that provides a urinary connection between the tip of the bladder and the placenta. At birth, this structure normally closes and gradually disappears as the umbilicus shrinks. Occasionally, this structure reopens and allows urine to drip from the umbilical stump. This is called a patent urachus. Patent urachus is sometimes seen when systemic infection or infection of the umbilical stump itself is present. It may also occurr following damage to the urachus as a result of excessive tension on the umbilical cord during birth. Infection of other umbilical structures may also damage the urachus and allow urine to leak into the abdomen. Clinical signs may not develop until later in life if the urachus is the primary problem.
Meconium is the name for the contents of the foals intestinal tract during gestation. It therefore becomes the first feces passed by the foal. It is a characteristic dark brown in color and very thick in consistency. Some straining is normal while the foal is passing meconium. Once this is passed the feces change to a yellow-brown color and are much softer in consistency. Normal foals do not defecate frequently, so once the meconium is passed is it common not to witness defecation very often. Constipation is not uncommon in neonatal foals trying to pass meconium; this condition is called a meconium impaction. A commercial enema can be given carefully to help pass meconium. If the foal continues to strain, multiple enemas should not be given at home, as this can cause irritation and discomfort which is also manifested by straining. Rather, a veterinarian should examine the foal. Medical treatment can be given orally and sometimes IV to help soften the meconium and encourage passage. On rare occasions, surgery is necessary to remove the blockage. Meconium impactions themselves are not usually a serious problem. However, secondary problems may prove challenging. If the foal does not nurse, it will become dehydrated, possibly hypoglycemic, and therefore more susceptible to infection. Occasionally, foals will develop impactions because they do not nurse for some reason - weakness or musculoskeletal problems, depression due to illness, etc. Prognosis for simple meconium impactions is excellent.
Navel Ill is infection of the umbilicus and/or its internal structures. This most often occurs within the first days to weeks of life. The external umbilicus may be swollen, painful, and warm to the touch; however it may also appear and feel normal. Drainage may be present in some cases. Infection is most commonly found in one of the internal structures of the umbilicus - usually in the artery or vein. Although no external abnormalities may be present at the umbilicus, the foal shows signs of systemic infection - depression, decreased appetite, and sometimes fever. Diagnosis is accomplished via ultrasonographic examination.
If navel ill is secondary to a systemic problem, other areas may also be affected (especially the lungs and joints). Foals can be treated conservatively (with antibiotic therapy) or surgically. Frequent monitoring via serial ultrasonographic evaluation is important to confirm that conservative therapy is effective. Surgical removal is sometimes necessary to eliminate infection. Dipping the navel immediately after birth with an antiseptic solution is recommended to help prevent navel ill. The most commonly used solutions include 1-2% iodine solution or 0.5% chlorhexidine solution. The umbilicus should be submerged in about 1/2 cup in a small mouth container (ie, syringe case, baby food jar, pill bottle) for a few seconds 3 times a day for the first two days of life. Exposure to pathogens and FPT also encourage the development of infection. Prognosis for foals with umbilical infections is guarded and often is dependent on the presence of secondary problems, especially joint or bone infection.