I have a horse which my farrier says should only have 1 net of hay a day due to red lines appearing on her front feet. can this be right when at present she is stabled 22 hrs a day? She is a Dales mare 14'2" and weighs approx 490kg I cannot ride at present but she is lunged or freeschooled everyday for 20mins minimum

Optional Information:
Age: 8; Female; Breed: Dales Pony

Already Tried:
restricted diet of 1 scoop happy hoof & 9kg of hay a day