Happiness: by analogy to humans happiness animal happiness would result from i) everyday sensational pleasure, ii) engaging with the environment, conspecifics and handlers and iii) realising own goals (Yeates & Main, 2008).
Yeates, J. W., & Main, D. C. J. (2008). Assessment of positive welfare: A review. The Veterinary Journal, 175(3), 293–300. https://doi.org/10.1016/j.tvjl.2007.05.009