What happens to animals that deprived of oxygen?

Animals will asphyxiate a condition in which the body and most importantly the brain lacks a supply of oxygen. which is called or known as oxygen deprivation

When Eukaryotic Cells (animal cells) experience a lack of oxygen, they lose a vital piece of the formula to creating ATP. ATP (Adenosine Tri-Phospate) is the universal form of energy throughout cells. ATP and ADP (Adenosine Di-Phosphate) are created in the mitochondria, and there Oxygen or "O2", Carbon, and Hydrogen come together to make ATP. This process is called cell respiration.

If you care for it, the formula is:

C6H12O6 - - - > 6 CO2 + 6 H2O + ~38ATP

That's why are breath has moisture, and we exhale CO2.

Without Oxygen, we couldn't generate energy, and bodily functions would cease!