Large dog breeds show faster biological ageing at the molecular level, a new study published on Oct. 8 in Science finds. Researchers analysed blood DNA from 894 companion animals enrolled in the Dog Aging Project at the University of Washington, constructing epigenetic clocks based on patterns of DNA methylation. The clocks estimated dogs’ biological ages and revealed that larger breeds accumulate age-related molecular changes more rapidly than smaller breeds of the same chronological age.
The team mapped chemical tags known as methyl groups, which sit on top of DNA and help regulate gene activity. Losses and gains of these marks followed predictable trajectories with age. Investigators identified a pronounced loss of methylation at regions called transposable elements—so-called “jumping genes”—in dogs with greater body size. That reduction of methyl tags can allow these elements to become more active, potentially disrupting other genes and promoting inflammation, a hallmark of ageing. Study authors including Blaise Mariner and Noah Snyder-Mackler at Arizona State University linked older-than-expected epigenetic ages with higher mortality risk among the animals studied.
Beyond the specific genomic changes, the research found that immune cells from older dogs become more similar to one another, a pattern described as loss of cell identity. Because immune cell specialization underpins functions such as cancer surveillance and infection control, this convergence may reduce immune competence with age. The investigators note that selective breeding for large body size could have favoured rapid growth at the expense of long-term maintenance, though the study does not establish a direct causal pathway for that trade-off. The authors plan to refine their epigenetic clocks as the Dog Aging Project continues to follow more animals over longer periods.
Findings in companion dogs carry potential implications for human health because pets and people share environments and many age-related conditions. By improving predictive models from methylation data, researchers aim to help anticipate age-related health risks in animals and to deepen understanding of conserved ageing processes across species and topics such as aging and epigenetics.
