Statements : Some rats are cats. Some cats are dogs. No dog is cow.

Conclusions :
I. No cow is cat.
II. No dog is rat.
III. Some cats are rats.

III is the converse of the first premise and so it holds.

Some rats are cats. Some cats are dogs.

Since both the premises are particular, no definite conclusion follows.

Some cats are dogs. No dog is cow.

Since one premise is particular and the other negative, the conclusion must be particular negative (O-type) and should not contain the middle term. So, it follows that 'Some cats are not cows'.