I have two cats who are nearly 16 yrs old. I have been noticing in the last several months that they are eating less amounts; they don't eat all of the food I put down. I have not increased the amount, but have even reduced the amount so there is not so much left over. Is that normal for older cats? Should I be trying to get them to eat more as before? And is there something I can add to the food to encourage them to eat more? I had read that alfalfa or an alfalfa syrup could help.