Loading horses (Equus caballus) onto trailers—Behaviour of horses and horse owners during loading and habituating

•20% of the horse owners interviewed experience loading problems.•Well habituated horses are loaded more rapidly and with less individual variation.•Novice horses show a higher heart rate inside the trailer compared to outside.•Novice horses show signs of habituation after three loading events.•Habituation may increase loading safety and horse welfare. Horses are transported for many reasons, and loading habituation is potentially affecting animal welfare and human safety. Horses are neophobic but may be habituated and trained to perform complex behavioural tasks in novel environments. Before transporting, horses should preferably be habituated to the vehicle and transportation. However, not all horse owners know how this can be done or how to apply common ethological methodology. The aim of our study was to quantify loading problems experienced by horse owners through a survey, compare horse behaviour during the loading procedure at a veterinary clinic with at competition sites and to perform a controlled experiment to investigate the effects of a standardized loading habituation procedure. Part 1 of the study was a horse owner survey. In study 2 we observed horses loaded at competitions and horses loaded at a veterinary clinic to compare two populations with differing habituation levels. In part 3 of the study six 2–3 year-old Icelandic horses were observed during loading habituation and heart rate was measured during these procedures over three consecutive days. Swedish horse owners’ written survey answers (n=99) showed that 21% experienced problems when loading their horses. Loading at the veterinary clinic took significantly longer (5.8min) compared to at the competition site (28s) (P