When I give Merlin a dose of Metacam he gets 4 ml, which is his last proper weight. Since then he is probably about 5 to 6 kilos. The 4 kilo dose is working though, and it is only now and again so I have no qualms whatsoever about giving it to him. If he is pain, echoing what Mark says, he is grumpy, uninterested in food, very unusual, Merlin loves his grub, etc. I would rather he was happy.