This does not directly answer your question but it's worth mentioning.

Animals rarely "re-spawn" in the normal Minecraft. Most animals you see spawn with newly generated chunks. That is, when you visit an area for the first time, animals are likely to spawn. However, re-spawning in an already visited area is rare.

Approximately one in ten newly generated chunks will contain mobs, usually in packs of up to four of the same species. They will always spawn on the highest available block in a column i.e. the one that can see the sky. For an animal to spawn on it, this block must be opaque and...

Very rarely, new animals can spawn in already generated chunks, just like monsters do. When animals spawn in this way, they do so only on grass blocks with light level 9 or greater above them. This is also a requirement for animals spawning from monster spawners. Unlike monsters, animals do not spontaneously despawn, except for wild ocelots and wolves (which can despawn only when they are hostile).

This leaves us with the question of whether the spawning behavior in Pocket Edition is any different.

Reference: Minecraft Wiki

This does not directly answer your question but it's worth mentioning.

Animals rarely "re-spawn" in the normal Minecraft. Most animals you see spawn with newly generated chunks. That is, when you visit an area for the first time, animals are likely to spawn. However, re-spawning in an already visited area is rare.

Approximately one in ten newly generated chunks will contain mobs, usually in packs of up to four of the same species. They will always spawn on the highest available block in a column i.e. the one that can see the sky. For an animal to spawn on it, this block must be opaque and...

Very rarely, new animals can spawn in already generated chunks, just like monsters do. When animals spawn in this way, they do so only on grass blocks with light level 9 or greater above them. This is also a requirement for animals spawning from monster spawners. Unlike monsters, animals do not spontaneously despawn, except for wild ocelots and wolves (which can despawn only when they are hostile).

This leaves us with the question of whether the spawning behavior in Pocket Edition is any different.

Reference: Minecraft Wiki

This does not directly answer your question but it's worth mentioning.

Animals rarely "re-spawn" in the normal Minecraft. Most animals you see spawn with newly generated chunks. That is, when you visit an area for the first time, animals are likely to spawn. However, re-spawning in an already visited area is rare.

Approximately one in ten newly generated chunks will contain mobs, usually in packs of up to four of the same species. They will always spawn on the highest available block in a column i.e. the one that can see the sky. For an animal to spawn on it, this block must be opaque and...

 

Very rarely, new animals can spawn in already generated chunks, just like monsters do. When animals spawn in this way, they do so only on grass blocks with light level 9 or greater above them. This is also a requirement for animals spawning from monster spawners. Unlike monsters, animals do not spontaneously despawn, except for wild ocelots and wolves (which can despawn only when they are hostile).

This leaves us with the question of whether the spawning behavior in Pocket Edition is any different.

Reference: Minecraft Wiki

This does not directly answer your question but it's worth mentioning.

Animals rarely "re-spawn" in the normal Minecraft. Most animals you see spawn with newly generated chunks. That is, when you visit an area for the first time, animals are likely to spawn. However, re-spawning in an already visited area is rare.

Approximately one in ten newly generated chunks will contain mobs, usually in packs of up to four of the same species. They will always spawn on the highest available block in a column i.e. the one that can see the sky. For an animal to spawn on it, this block must be opaque and...

Very rarely, new animals can spawn in already generated chunks, just like monsters do. When animals spawn in this way, they do so only on grass blocks with light level 9 or greater above them. This is also a requirement for animals spawning from monster spawners. Unlike monsters, animals do not spontaneously despawn, except for wild ocelots and wolves (which can despawn only when they are hostile).

This leaves us with the question of whether the spawning behavior in Pocket Edition is any different.

Reference: Minecraft Wiki