Thats absurd. You have never seen puppies or otters playing or colts frolicking on a sunny day?
Animals operate on instinct. They don't have will. Animal play is part of their instinctive behavior, and a sign of animal health or "contentment."
This differs radically from human joy:
joy ( P ) Pronunciation Key (joi) n.1) Intense and especially ecstatic or exultant happiness. The expression or manifestation of such feeling.
2)A source or an object of pleasure or satisfaction: their only child, their pride and joy.
I think we tend to anthropomorphize animals. I know, I used to have a couple of dogs.
St. Thomas nowhere treats in detail of animal instinct, but his position on the subject is rendered none the less clear from a great many passages in the "Summa Theologica". He is in full agreement with the best modern authorities in laying chief emphasis on the absence of consciousness of the end as the essential characteristic of instinct. He says (op. cit., I-II, Q. xi, a. 2, C.): "Although beings devoid of consciousness (coqnitio) attain their end, nevertheless they do not attain a fruition of their end, as beings do who are endowed with consciousness. Consciousness of one's end, however, is of two kinds, perfect and imperfect. Perfect consciousness is that by which one is conscious not only of the end, and that it is good, but also of the general nature of purpose and goodness. This kind of consciousness is peculiar to rational natures. Imperfect consciousness is that by which a being knows the purpose and goodness in particular, and this kind of consciousness is found in brute animals, which are not governed by free will but are moved by natural instinct towards those things which they apprehend. Thus the rational creature attains complete enjoyment (fruitio); the brute attains imperfect enjoyment, and other creatures do not attain enjoyment at all."