Some reasons an ultrasound may be recommended for your pet:
To evaluate masses in the abdomen (although only an actual biopsy can diagnose)
To evaluate liver problems revealed in blood work
To enable sterile urine collection
To characterize fluid in the chest or abdomen
To do a pregnancy check (surprisingly, we cannot count the babies this way, they are too mobile!)
Why does my pet's hair need to be shaved for an ultrasound?
The ultrasound probe needs to be in direct contact with the skin in order to transmit readable images.
Why might my pet need sedation for an ultrasound?
In order to gather clear pictures, the pet cannot move. It would be like trying to take a still picture of a moving target--only blurry images result.