Final answer:
Bilirubin is usually not present in the urine of healthy animals, but its presence in horse urine indicates disease, making horse the correct answer to the student's question.
Step-by-step explanation:
Bilirubin is a brown pigment secreted into bile by the liver and is a byproduct of the catabolism of dead red blood cells.
It is mostly excreted in feces by the large intestine after conversion into stercobilin, which gives stool its characteristic color.
Normally, bilirubin is not detected in the urine of healthy cows, horses, dogs, or cats. However, in diseased states, such as liver disease or biliary tree obstruction, bilirubin can appear in the urine, a condition known as bilirubinuria.
The correct answer to the student's question, that bilirubin is not detected in normal urine of the species in question and indicates disease if present, is horse (c).