I don't think it affects them very much. I've seen fields and hunted fields that were spread with manure, and it seemed to almost attract them. If cattle are fed whole kernal corn a lot of it passes right through them and geese will pick throughmanure for the corn. Maybe the field you are talking about had been spread with manure with little or no corn in it, and the manure covered up whatever food source they were going there for ... or the gees just moved on to another field.