The law of Karma is universal, i.e., applicable to all equally and applicable the same manner across time.
Humans are smart hence they can have the Right View but in the case of an animal this is not the case. Also an animal acts mainly by instinct which is Unprompted.
So the state of mind a hunting animat can have is:
- One consciousness, unprompted (instinct), accompanied by pleasure (pleasure of a good meal), and connected with wrong view (lack of belief of repercussion and consequences of Karma or action)
- One consciousness, unprompted (instinct), accompanied by indifference (pure instinctive reaction), and connected with wrong view (lack of belief of repercussion and consequences of Karma or action)
The above 2 mindd states generate more heavier Karma than the other.
Also animal will have following mental content which in humans have a choise to eliminate:
- Ahirika - not ashamed of doing evil
- Anottappa - no fear to do evil, i.e., fear of the consequences
Also in the animal kingdom fear, hunger, greed, territorial attachments, etc. is predominant which gives arise to unwholesome states and opportunity and intellect to do +ve karma is less.
This all point to that in the animal kingdom you are worse off and would end up accumulating more bad karma. Also if you are a carnivore feeding and survival needs killing as you simply cannot become herbivore, hence the nature of your birth will mean you tend to accumulate more bad karma.
Ref: Manual of Abhidhamma by Ven. Narada, Comprehensive Manual of Abhidhamma, Do lions create bad kamma for their next life when they kill?