Which environmental factor does NOT significantly influence animal growth?

Day length, while it can play a role in certain physiological processes and behaviors in animals, does not significantly influence overall animal growth compared to the other factors mentioned. Temperature is crucial because it affects metabolic rates and the efficiency of feed conversion—higher or lower temperatures can lead to stress that impairs growth. Humidity also plays an important role, especially in the comfort levels and health of animals, influencing respiratory rates and susceptibility to disease, which in turn can affect growth. Space availability is critical as well; overcrowding can lead to competition for resources, stress, and reduced growth rates.

Overall, while day length might influence reproductive behaviors or breeding cycles in some species, it does not directly impact the animal's growth in the same way that temperature, humidity, and space availability do.