Anatomy

The developing fetus resides within the uterus, in the abdomen. The placenta develops between the uterus and the fetus and is responsible for supplying the fetus with all its nutritional requirements during development in the uterus. The placenta has several component parts, including the umbilicus (Fig. 1.). There is the outer membrane known as the chorioallantois, which is attached to the internal surface of the uterus, known as the endometrium. This outer membrane forms a sac, inside of which is the allantoic fluid. There is a second membrane within the outer one, known as the allantoamnion. Inside this membrane is the amniotic fluid, within which the fetus floats. The two membranes come together at the umbilical stalk. The umbilicus has an amniotic portion and an allantoic portion, as it passes through the appropriate sacs. Within the umbilicus are two umbilical arteries and one umbilical vein. These vessels allow the exchange of blood between the fetus and the placenta; the placental blood is supplied by the mare. The umbilical cord also contains the urachus, which is a connection between the fetal bladder and the allantoic sac. The fetus produces urine, which is excreted into the allantoic sac; this is the outer sac, not the one that the fetus is floating in. The umbilicus can be between 50 and 100 cm long, allowing the fetus a great deal of movement within the placenta.

When the umbilical cord ruptures at birth, the urachus normally closes within a few hours by fibrosing. However, this process can fail, or the urachus can reopen several days after birth. A very long umbilical cord or partial torsion (twisting) of the cord are believed to be possible causes of patent urachus, by causing excess tension on the umbilical cord where it meets the body. Affected foals are noticed to be persistently moist around the umbilicus, or else urine can be seen dripping or streaming from the umbilicus. Patent urachus can also occur secondary to infection of the umbilicus, known as omphalitis.

Affected foals are usually bright and alert. However, if the urachus is inflamed and this inflammation has ascended and is involving the bladder, affected foals can be depressed, inappetant and repeatedly strain to urinate(known as stranguria). Also, if the patent urachus is due to an umbilical infection, these foals can be very sick as omphalitis can be part of a more widespread infection, known as septicaemia. Septicaemic foals often have other focuses of infection, such as the joints, which become very effused (swollen) and painful. Leakage of urine from the urachus can result in urine scalding of the area around the umbilicus and down the inside of the hindlegs.

Investigation

When the veterinarian examines the foal, they will perform a general physical examination, including listening to the heart and the lungs, and taking the foal’s temperature. The vet will observe the abnormal urination and palpate the umbilicus. If the umbilicus feels abnormal, this may indicate that an umbilical infection is present. However, only the external parts of the umbilicus are palpable. In order to examine the internal parts of the umbilicus, it is necessary to perform an ultrasound examination of the umbilicus and abdomen. If the umbilicus is infected, an abscess can be seen within one of the structures that forms it, such as the two arteries or the vein, or the urachus itself.

The vet will question the owner about the events surrounding the birth of the foal. For example, did the mare run milk prior to foaling? If so, how much milk do you think she lost? Also, how soon after birth did the foal drink and did it drink well? All these questions are aimed at establishing if the foal received adequate colostrum. A blood test can be performed to try to quantify the amount of colostrum the foal received. Colostrum is extremely important because it provides the foal with protection against infection. If there is any question about the foal receiving adequate colostrum, a plasma transfusion is advisable to provide the foal with extra protection against infection by supplying it with antibodies.

Although a patent urachus can cause straining, the vet should check newborn foals for meconium impaction. Meconium is the first manure that the foal passes. It can be very dry in some foals and difficult for them to pass, which causes them to strain. Meconium impaction can occur concurrently with a patent urachus. It is treated by the administration of enemas, which soften the impacted meconium, allowing it to be passed.

Treatment

In the past, owners of foals with a patent urachus were advised to cauterise the umbilicus with chemicals, such as silver nitrate or concentrated iodine solution. However, this treatment is no longer recommended. The logic behind using chemical cauterisation was to cause inflammation and swelling, which will cause closure of the urachus. However, the amount of irritation caused by the chemicals to the tissues can predispose the area to infection, which puts the foal at risk of becoming septicaemic, or at least developing a local infection (omphalitis). In some cases the area will already be infected, which is why the urachus is patent in the first place, so it is not advisable to further promote infection.

Nowadays, if the foal is otherwise healthy, it is placed on a course of broad spectrum antibiotics. The antibiotics will treat any infection that may be present, or otherwise protect the foal from the development of an infection. The umbilicus is not treated directly. Many cases of patent urachus close spontaneously. It can take several days to weeks for the urachus to close, but it usually will as long as there are no other factors involved. Different vets recommend waiting for different amounts of time, some say one week and others say a month. The amount of time given to the foal is not critical, as long as the foal remains bright and healthy during this time. If there is ongoing infection, then it is unlikely that the urachus will close on its own. In these cases, surgery is necessary to close the urachus. If there is evidence of umbilical infection as well as a patent urachus at the time of the initial examination, it is recommended that these foals be referred for surgery straight away. It is imperative that the infected tissue is removed before the infection spreads to other areas of the body, such as the joints. In some cases, the infection has already spread, but it is still important to remove the infected tissue.

Barrier creams, such as Vaseline®, can be applied to the area around the umbilicus and the insides of the legs to prevent urine scalding the skin.

Summary

• Patent urachus can occur from birth or appear a few days after birth. 
• Diagnosis is straightforward, by the observation of urine leaking from the umbilicus. 
• A veterinary examination is important to establish if the problem is simple or complicated by infection of the umbilicus. 
• Simple cases are treated with antibiotics and time to allow the urachus to close spontaneously. 
• Complicated cases require surgery to remove the infected tissue and close the urachus. 
• The application of chemicals to cauterise the urachus is not recommended.