Equestrian leisure activities have indisputably grown in France during this last decade. This development affected riding schools but also the number of Equidae purchases for leisure. This Equidae owners have the choice, for the various tasks necessary to take care of their Equidae, between buying them (using a service supplier), and producing them (for example taking care of their Equidae at home). We proposed an original application of the Transaction Costs Theory (TCT) (Williamson) in order to explain Equidae owner choice for delegating or integrating the various tasks necessary to take care of their Equidae. We tested a set of explanatory factors of their choice among which we considered transaction costs. Original data were produced in questioning face-to-face Equidae owners and statistic treatments were done. The results showed that the TCT actually contributes to shed some aspects of the decision process but other factors have also to be taken into account.