Livestock

Zakaat on free grazing animals

Q: If a person has animals that are grazing on his land without him feeding them himself, will they be zakatable even though they only graze on his privately owned land (which is fenced off)? The animals are only for breeding or milking. The animals referred to are cows. I know that there is zakat if they are freely grazing but I am unsure if they are counted as freely grazing if they are doing so on privately owned and fenced off land? If possible, could you please provide a reference to the answer?