A recent study done by PetSmart shows only about 1/4 of "new pet parents" chose to get their animal from a shelter. About 1/3 of "new pet parents" have NOT had their animal spayed or neutered. You can read the report here http://petsmartcharities.org/research/
Another big problem is wrong animal - wrong person. People obtain animals, particularly dogs and horses, without fully understanding their behavior and health requirements. I am floored when I hear people complain that their Jack Russell / boxer / border collie is "hyper," or their Great Dane / bullmastiff is "too big," or their Newfoundland / Siberian husky / Pomeranian "sheds too much." They are "surprised" that a horse need more food than grazing the weeds in their backyard, or that their hooves get overgrown from standing in mud and sand all day.
We often hear about animals needing new homes. How have you addressed the issue of unwanted pets? Do you take them in permanently? Do you foster until they find a home? Do you ask around, trying to find a new home? Do you take the animals to shelters? Do you trap/neuter/return feral cats?
How do we prevent these problems in the first place?