Not that I have ever tasted haylage you understand, but assume that is what is tainting the milk. Although Bramble and Alyce are outside during the day, they do have access to haylage too, and obvously at night. Due to the heavy rain, they have been running inside,and probably eating the haylage more than the grass!!
Yesterdays milk tasted awful - but the farm cats did not notice. A local farmer bottles his own milk, and he had tons of complaints one winter, because the milk tasted funny - that was the silage.
I would feed hay, but the only ones I can get are the very long bales - unable to move them. And they are £70!!