['Telomere length and telomerase activity are important indicators of cellular senescence and replicative ability. Loss of telomerase is associated with ageing and the development of osteoarthritis. Implantation of telomerase-positive cells, chondrocytes, or stem cells expressing a normal chondrocyte phenotype is desired for cartilage repair procedures. The objective of this study was to identify at what age chondrocytes and at what passage bone marrow-derived mesenchymal stem cells (MSCs) become senescent based on telomerase activity. The effect of osteogenic protein-1 (OP-1) or interleukin-1α (IL-1α) treatment on telomerase activity in chondrocytes was also measured to determine the response to anabolic or catabolic stimuli.', 'Articular cartilage was collected from horses (n = 12) aged 1 month to 18 years. Chondrocytes from prepubescent horses (<15 months) were treated with OP-1 or IL-1α. Bone marrow aspirate from adult horses was collected and cultured for up to 10 days to isolate MSCs. Telomerase activity was measured using the TeloTAGGG Telomerase PCR ELISA kit.', 'Chondrocytes from prepubescent horses were positive for telomerase activity. Treatment with IL-1α resulted in a decrease in chondrocyte telomerase activity; however, treatment with OP-1 did not change telomerase activity. One MSC culture sample was positive for telomerase activity on day 2; all samples were negative for telomerase activity on day 10.'] Does telomerase Activity in Articular Chondrocytes be Lost after Puberty?