Final answer:
The urine dipstick test for urobilinogen is the least useful in animals, unlike tests for pH, glucose, and bilirubin, which can diagnose specific health issues.
Step-by-step explanation:
The least useful test on a urine dipstick for animals is the test for urobilinogen. In veterinary diagnostics, urobilinogen has little clinical relevance, because it is a normal constituent of urine and its levels do not typically reflect disease processes in animals as they can do in humans. Tests for pH, glucose, and bilirubin are generally more useful in animals, as they can indicate conditions such as urinary tract infections, diabetes, or liver disease, respectively.