North American Veterinary Licensing Examination (NAVLE) Practice Test

The primary symptom of a retained placenta in dairy cows is the presence of a foul-smelling discharge. When the placenta is retained, it can lead to an accumulation of bacteria and necrotic tissue, resulting in a pungent odor. This discharge can be a strong indicator of infection and inflammation of the uterus, known as metritis, which often accompanies retained placenta.

While weight loss, depressed appetite, and fever can also be associated with retained placenta and subsequent uterine infection, they are more general symptoms that can arise in various conditions. The foul-smelling discharge is more specifically linked to the complications that arise directly from the retention of the placenta, making it the most distinctive and primary symptom to note in this scenario.