I was doubtful when I saw the words коровье молоко and козье молоко. Then I checked an electronic dictionary (Толковый словарь русского языка for Mac), and there -ья/-ье where referred as the replacements for -ий in their respective adjectives.
So far I knew that there are, in Russian, hard adjectives (красив.ый, -ая, -ое, -ые), soft adjectives (соседн.ий, -яя, -ее, -ие) and mixed adjectives resulting from the spelling requirements after some consonants (хорош.ий, -ая, -ее, -ие).
Is ья/ье an irregular soft ending? Does it decline just like the regular soft endings (in which feminine genitive is -ей and neuter genitive is -его)?