Cats and vomiting

Question
I, too, have 5 cats.  One vomits a lot (female, 4yrs. old), one vomits sometimes (also has asthma), and three who never vomit.  Why does she vomit, why does it stain the carpet yellow no matter what I use to clean it with, and what can I do to help her stop?  I feed them "hairball treatment" dry food.  They all eat from the same dishes, drink from the same bowl, and use the same litter box (a very big one that I clean twice a day).  Also she is the smallest of the cats, gets picked on sometimes and is very gentle.  What else can I tell you?  Please help.

Answer
Hi there!  There are a lot of reasons cats vomit.  It is normal for them to vomit every now and then from stress, change of food, hairballs, ect.  It is, however, not normal to be vomitting a lot.  I take it that she has been vomitting for a while, maybe even most of her life.  Here are some suggestions as to what may be causing this.
First, if she is vomitting a staining yellow substance, this is probably stomach bile.  A lot of animals vomit when hungry, and it will appear as you have described.  You have mentioned that she is the smallest cat and gets picked on.  Is it possible that the other cats are not allowing her to eat as much as she needs?  It is very common to have one cat that the rest pick on.  This cat, in a multi-cat household, will be very gentle, thin and sweet.  Sometimes this kitty is "not allowed" to eat her desired amount, as the others bully her.  Being that she is now still hungry and stressed about being bullied, this would cause a stomach upset.  If you have witnessed this sort of behavior during feeding, it may be beneficial to begin feeding this kitty at least one meal by herself.  This way you know that she is receiving adequate nutrition.  I have a little kitty in my household that is picked on as well, and I had to resort to feeding her in this manner and found it very helpful.
Second, cats are known to have extremely odd, and sometimes never diagnosed gastro-intestinal problems.  This ranges from Irritable Bowel Disease, Gastritis, Colitis, Gastric Ulcerations, Mega Colon, Acid Reflux, and Immflamatory Disease.  These are only a few.  The list is so broad and the symptoms are often times alike from ailment to ailment.  For most gastro-intestinal problems, you will notice vomiting, diarrhea, lack of appetite, increased water intake, frequent trips to the litterbox and sometimes lethargy.  You may see one of these symptoms, or you may see all of them.  Generally an x-ray and some blood work can give your veterinarian an idea about what's going on inside your cat.  Most gastro-intestinal disorders are treated by sporatic steroid injections (to decrease inflammation), pepcid like medications to sooth the stomach like Sucralfate, and a special diet.
Third, has she ever been tested for Hyperthyroidism?  Hyperthyroidism is actually quite common in cats.  She is the perfect candidate...small and vomiting.  These are the symptoms of this ailment and this can be diagnosed by bloodwork and treated with medications like Soloxine, or Thyrone.
And last, it may not be a bad idea to have her blood sugar level/glucose level checked to be sure that her body's insulin levels are normal.  Often times a cat with low or high sugar in their blood tend to vomit.  Again, this is treatable as well.
All of the ailments that I have described are treatable, and most for a reasonable price.  I would highly recommend a physical examination by your veterinarian to be sure that your kitty is strong and healthy.  I wish I could tell you exactly what is going on, but unfortunately, the above ailments are the furthest I can narrow it down without actually seeing her.  I hope this has been helpful and puts your heart at ease.  
Please give that little girl tons of kisses for me, and please keep me posted as to what is found.
Hilary