Adult male horse data from Conger and Frisco Herd Management Areas, Utah, USA, between 2017 and 2020

We studied the effect of castrating a proportion of the adult males in a feral horse herd to examine any effect on behavior and social associations, particularly in terms of association with mares (i.e., maintenance of a harem group). We conducted this study between 2017 and 2020 at two Herd Management Areas (HMAs) in western Utah, USA: Conger and Frisco. We conducted demographic observations year round at both HMAs to record group composition and foaling rate. We additionally recorded behavioral observations at Conger HMA.