Bruises on cattle carcass affect the quality of the meat and are indicators of poorwelfare conditions. According to the literature the occurrence of bruises is related to preslaughter conditions, however their contribution is not clear for Chilean cattle. The aim of this thesis was to provide a better understanding of the relationship between pre-slaughter factors and the occurrence ofbruises -from loading until slaughter- under Chilean conditions.Therefore in the first study slaughter records of two Chilean slaughterhouses were analysed.It showed that cows and oxen had higher risk to present bruises compared to steers andheifers. Moreover, animals that passed through a livestock market were more prone to present bruises than animals that carne directly from the farm. A large difference in carcass bruise prevalence was found between slaughterhouses and this discrepancy was attributed to differences in the use of the Chilean scoring system and to several constraints of the system itself. Thus a new scoring system was developed and its reliability was assessed showing a high agreement when only one observer performs the scoring. An inventory of the grosscharacteristics of bruises, based on the refined bruising protocol, was carried out. Animals passing through a livestock market have more bruises than animals transported directly from the farm to the slaughterhouse. This thesis presents evidences of rough handling and animals beaten by sticks at markets. In the last study the causal event of bruises during the preslaughterperiod was assessed. It showed that rough handling due to inappropriate use of aidsto drive animals during loading and unloading, and inadeq quate stunning facilities at the slaughterhouse were the areas of most risk for bruising. It was concluded that improvements in the design and maintenance of appropriate structures and training of stock people willreduce the occurrence of bruises and in consequence will lead to better welfare conditions of cattle for slaughter.PFCHA-BecasDoctorado en Ciencias Agrarias140p.PFCHA-BecasTERMINADA