Which of the following is a secondary site for pulse oximetry placement in canines?

The skin around the penis is considered a secondary site for pulse oximetry placement in canines due to its relatively thin tissue and good vascularization. This makes it possible to obtain a reliable reading of the dog's blood oxygen saturation levels. In situations where more common measuring sites, such as the tongue or paws, might be less accessible due to factors like injury, trauma, or other conditions, using the skin around the penis provides an alternative.

While other areas may have some merits for monitoring pulse oximetry, they may not be as effective. For instance, the tongue is typically a primary site due to its rich blood supply and convenience in most assessments. Paw pads can be used as well, but factors like ambient temperature or injury could affect readings. The tail may also serve as an alternative but may not provide the same accuracy and consistency as using the skin around the penis, especially in field conditions where blood flow dynamics might change in response to stress or temperature. Thus, the skin around the penis serves as a viable secondary site in canine pulse oximetry.