Three dogs of the Perro de Presa Canario, a.k.a. Canary Mastiff breed were used to play the role of De Niro. Their names were Curly, Ademar and Han Solo. Each of them had a different task. One more dog of the breed appears in the movie - a little puppy. It was given as a present to Yariv Lerner, CEO of Nu Boyana Film Studios, where the movie was shot. The puppy was named De Niro.
The "cast" is followed by the "animal cast" in the end credits. It's not just the dogs who play De Niro who are listed--pretty much every animal is listed by name, right down to the cow and chickens on Gage's farm and Walker's yellow fish.
There are more animals listed in the animal cast (20) than humans in the cast (18) in the end credits.