Simple SummaryHorses are often transported, and transport may impair their health and welfare. However, there is no tool to assess objectively their welfare after transport. This study aimed to develop the first tool for measuring horse welfare on arrival and to propose a scale to rank horses based on their welfare impairment. The tool and the scale were developed based on the literature and expert knowledge using data collected from 1019 horses traveling to three slaughterhouses. The results of a checklist containing 15 animal-based measures (ABMs), recorded on arrival, were assigned a level of welfare impairment (S). Based onS, the horses were split into four categories: good shape; light affected; affected; down (GLAD). Based on the GLAD scale, G horses can be slaughtered immediately, L horses need rest, A horses need attention and treatment, and D horses may need euthanasia or emergency slaughtering. The majority of the horses fell into the categories G (43%) and L (48%). Our tool is a simple, easy-to-use instrument to assess horse welfare after transport, specifically aimed at horses arriving at slaughterhouses, and it may assist competent authorities in deciding when a horse can be slaughtered.AbstractTo date, there is no official method for measuring horse welfare after transport. This study aimed to develop a scale to classify horses into four categories: good shape; light affected; affected; down (GLAD) based on their welfare impairment measured at unloading. To this end, 15 animal-based measures (ABMs), previously recorded from 1019 horses, were scored. Weight and severity scores provided by welfare experts, alongside the number of welfare principles highlighted by the ABM, were assigned to each ABM. The welfare impairment (S) of each horse was then calculated as the weighted sum of the severity scores of the 15 ABMs. Three thresholds were also set to define the four GLAD categories; the ABM “down” (i.e., horses unable to stand and walk on arrival, also considered by the law as the indicator of the worst welfare) was used as the higher threshold,Sdown, (category D); the intermediate threshold,S2, was defined by the ABM “injuries”, assumed to represent highly impaired welfare (category A); the threshold,S1, was defined assuming that significant welfare impairment starts from 20% ofS2(L category). Horses with anSvalue belowS1were considered physically and mentally fit (G category). Out of 1019, 43% of horses fell into category G, 48% into L, 9% into A, and 0.3% into D. Our scale could be useful for veterinarians to decide whether a horse can be slaughtered immediately (G), needs rest (L), needs attention (A), or euthanasia (D), but further validation is needed.