The urachus is the tubular connection present in the fetus between the bladder and the umbilicus. During gestation, urine flows from the bladder through the urachus into the allantoic sac.
As the fetus gets closer to term, more and more urine flows through the urethra, until ideally at birth all urine should exit the bladder through the urethra and the urachus should involute.
Foals can be born with a persistent urachus if closure fails due to excessive torsion on the umbilical cord in utero, or they may develop a patent urachus in the first several days of life due to ligation of the umbilical cord, omphalophlebitis, lifting of the foal under the abdomen, or straining due to constipation.
Tx for patent urachus may be medical or surgical depending upon whether the umbilicus is infected and if there are rents in the urachus within the abdomen.
Click here to see a good summary on patent urachus in foals, with images, courtesy of the American College of Veterinary Surgeons (ACVS).
