I think the answer depends on context:
For example, if you are trying to determine how much food to stock up on to ensure that all the animals are fed enough, you'll want to round up (over-estimate).
However, if you are trying, say, to determine some sort of guarantee that the number of animals will be at least some particular number (contract with a pet supply store to deliver $x$ animals, then you'd round down to ensure you can deliver as agreed.) Or if you want to report some statistical claim about $x$ number of animals ....., then for the purposes of most accurately reporting this, if it needs to be an integer, would be to round down.
So the question is ambiguous, and we'd need to know how you computed a non-integer number to represent animals, and what the context in which the need to round up or down is necessary.
Mathematically, dealing with strict rounding, the convention is to round down for fractions x such that $0 \lt 0.5$, and to round up for fractions x such that $0.5\leq x \lt 1.0$