Animal welfare is assumed to be influenced by the cumulative effects of positive and nega-tive events experienced by an individual. The present study investigated the levels of cor-tisol, relative telomere length and the association of these variables with the perception of canine age (apparent age). Firstly, it was investigated whether dogs' telomere lengths from dried blood correlated with the ones measured from oral swabs from the same individuals. As a correlation between samples from these two tissues were found we validated the use of buccal swab sampling to obtain dogs' relative telomere length. We then investigated whether dogs' relative telomere length present in buccal cells co-varies with glucocorticoid levels, results showed association between these factors. Since glucorticoids are the most used physiological parameter to assess animal welfare our results suggest the use of rela-tive telomere length as a potential to evaluate animal welfare. We investigated if the differ-ent backgrounds of dogs were associated with relative telomere length. Results showed that dogs from different background, sex and with different activity levels had significantly different relative telomere lengths. We investigated whether dogs' relative telomere length would vary over a one-year period, and results showed that the implementation of social enrichment can increase relative telomere length of laboratory dogs. Finally, we investigat-ed if a novel approach, estimating apparent age, could be used as a tool to assess wel-fare. Results showed that a dog's apparent age assessed from photographs could, poten-tially, be used as an animal welfare assessment method since people were able to identify dogs that were prematurely ageing. In conclusion, telomere attrition and apparent age can be used to indicate a dog's welfare.