I am assuming 100 is in D2 and 99 is in D3. Then the formula for D3 and
down is:

=$D$2-COUNTIF($C$3:C3, "dog")

Alternatively, if you have the words dog, dog1, cat, cat1 etc in D1, E1
etc, you can use the following formula in D3 and copy accross and down:

=$D$2-COUNTIF($C$3:C3, D$1)

HTH
Kostis Vezerides