1. Agriculture is a permitted activity - ie you don't need planning permission for it.
2. Non-permanent structures eg pig arks don't need permission, and fences less than 6ft high also don't require planning permission
both the above can be restricted by deeds, or if you rent or lease ( keeping of animals is a common restriction)
Otherwise it's all fine.
The only issue is nuisance caused by either noise or smell.
Noise is only an issue at feeding time, and then only for however long it takes you to get some feed down, and only an issue if you have large numbers.
Smell can be an issue if you keep larger numbers, but say 2-4 in a reasonable area should not give rise to smell.
You should not need to 'poo pick' on good ground, the worms and rain will deal with it.