Dear John,
Thank you very much for your help.
At first, I thought the sentence in question "They can also make soothing companions...." is parallel to the first sentence of this paragraph, "Pets are good for our mental health as well as our physical health." So, I thought, this paragraph has two points: dog ownership is good for mental health, and that dogs make excellent company.
So, I thought "also" is there because the sentence in question has introduced this second benefit of dog ownership.
Could this interpretation possible? I know usually English paragraphs have only one point to make in each, so this reading of mine is rather difficult, isn't it? Should the point of great companionship of dogs be thought to be included in the topic sentence?
Kamo