This is part and parcel of living in the countryside as the process of 'spreading' is a key factor in successful farming. Unfortunately the weather and positions of fields and crops dictate when farmers can spread. This often coincides with warmer days when people have windows open or are enjoying their gardens. The odours usually last for a short period of time and farmers are encouraged to use best practice whilst spreading muck in their fields.
Agricultural odours in a country location are not likely to be investigated by environmental protection unless they are excessive and are identified to be as a result of bad agricultural practices.