Letters 74.15

Besides, many things which are wont to be regarded as goods are granted to animals in fuller measure than to men. Animals eat their food with better appetite, are not in the same degree weakened by sexual indulgence, and have a greater and more uniform constancy in their strength. Consequently, they are much more fortunate than man. For there is no wickedness, no injury to themselves, in their way of living. They enjoy their pleasures and they take them more often and more easily, without any of the fear that results from shame or regret.

Seneca, Letters to Lucilius 74.15, translated by Richard Mott Gummere