We have a 3 year old Nubian doe and in about 1 1/2 weeks she went from giving about 2 quarts to 1/2 quart. Nothing changed in her diet, she acted the same, and I milked her on the same schedule I had for about 5 months. I want milk alot longer than this. Any ideas why she would dry up that much in that short of time? Thanks in advance.