My 4 year old border collie mix got neutered about 2 months ago. We have always just let him eat when he wants and we fill his bowl whenever its empty. He looks like he has gained weight and i dont want him to be overweight. Last time we checked he weighted about 20 kilos but i think he is more now. We used to give him too little exercise but now much more. We feed him Pedigree pet food and sometimes canned food too. How many times a day should he eat and how much?