Smaller the animals:

Explanation

Larger the organism, more is the distance covered for circulation of blood inside the body...so, more time is taken to circulate blood to each and every part of the body, which will further affect the heart beat and also lower the breathing rate, so breathing will be deep, but it's rate is slow incase of huge animals like a whale. But, incase of smaller organisms, the blood circulation is faster due to smaller body eg. a Shrew or a Rat, since distance to be travelled by circulating blood will be very less...so, breathing rate will be faster here.