Don't do cat meself much ! mine have always been pretty big, but would maybe be looking as to the reason she were so thin myself if she were mine ! assuming she is wormed, so hope that some of the catty folk can maybe come up with some suggestions!

Im not a catty person either but I know cats can suffer from hyperthyroid and they loose weight in spite of eating lots. Usually their coats get an unkempt appearance too. I know in dogs who usually go the other way Hypothyroid they gain weight and become lethargic not hyper like cats, can get this quite young so maybe cats can too. Theres 2 types in dogs idiopathic and autoimmune. It requires a blood test to diagnose it. As I said I havent had cats for years but I know its a pretty common problem in cats as it now is in dogs. Especially in the breeds I have. Im now on my third one with it.

Thank you all for your advice!

She was the vet yesterday evening. He said if it was an underlying condition she would be displaying at least one other symptom than just the weight loss and he couldn't find anything! She's perfectly healthy, just thin. (Liz you were correct!

The failure to gain weight is due to high levels of estrogen, which are increasing her metabolism. Because of the high metabolism and her high activity levels, she's burning most of the calories she consumes very quickly.

She's also not as thin as she appears. At least not to a malnourished point. He could not feel individual spinous processes and there is fat covering her ribs. The only place she feels/looks thin to him is along her midline, and he says it's just metabolism. Apparently I have nothing to worry about as long as she's still eating her fill and is still energetic.

I probably should have bred her sooner (though the vet still recommends I wait until she's a least a year old), and I won't make that mistake again.

Liz: I can't put her on Ovarid. It's not approved for use in cats in Canada, so no vet will/can prescribe it.

Sled Dog Hotel: Hyperthroidism is extremely rare in young cats. The vet didn't even think it a possibility, and he said she would be showing other symptoms. It usually appears around the same age as diabetes (senior years).

Thanks again!!!

Well then, get her mated asap - though if you're in Canada surely cats go off call during the autumn and winter don't they, unless you live in a hothouse?! I'm sure she's fully grown so I can't see that waiting until she is a year old is going to be of any benefit at all in your case.

Liz