To take rebirth in the higher realms, lower realm beings must have created the causes to be born there. With the convergence of suitable conditions and the said causes, the lower realm being will be able to take rebirth in the higher realms.
However, once one took rebirth in the lower realms, it is extremely difficult and very rare to be able to get out from the three lower realms! One has to remain there for an extremely long period of time until the negative karma to be there are completely exhausted!
Conditions that will trigger the ripening of their good karma to be reborn in the higher realms are almost impossible to come by! It one is born as an animal, unless one has the the good fortunes to be raised by a Dharma practitioner, chances of the animal to be reborn in the higher realms is slim and will take a longer time as described above. Animals are ignorant and constantly creating more and more negative karmas to go down further into the lower realms; they would kill to survive for example. Animals simply cannot practise Dharma, or collect merits or transform their minds.
Hence wherenever possible, we should help bless the animals, perform animal liberation, pray and dedicate merits to them, help them to take refuge with the Three Jewels ..... these would help the animals to create causes to be reborn in the higher realms in the future.