Telomere Dynamics in Livestock

SIMPLE SUMMARY: Short repeated sequences of DNA at the end of chromosomes are called telomeres; these help to maintain the chromosome structure. During normal cell replication, some of the sequences are lost; therefore, the length of telomeres may be associated with the aging of the overall animal. Longevity in livestock is difficult to measure and improve; however, telomere dynamics may represent an opportunity to monitor or influence longevity. Beginning in the 1990s, livestock clones were studied with respect to the change in telomeres because cloned DNA was often from a mature animal and, therefore, might have shorter telomeres associated with age. However, results differed by the species and cell type used to produce the clones. Telomere dynamics have been best characterized in dairy cows, pigs, and horses. In general, older animals have shorter telomeres, and stress imposed upon animals results in shorter telomeres; however, exceptions have been observed to both generalities. Attrition and other telomeric characteristics have been less well described in beef cattle, goats, and sheep. Longevity is measured uniquely and differs for species and production systems within the same species; therefore, it is appropriate to encourage the telomere-longevity correspondence in each. ABSTRACT: Telomeres are repeated sequences of nucleotides at the end of chromosomes. They deteriorate across mitotic divisions of a cell. In Homo sapiens this process of lifetime reduction has been shown to correspond with aspects of organismal aging and exposure to stress or other insults. The early impetus to characterize telomere dynamics in livestock related to the concern that aged donor DNA would result in earlier cell senescence and overall aging in cloned animals. Telomere length investigations in dairy cows included breed effects, estimates of additive genetic control (heritability 0.12 to 0.46), and effects of external stressors on telomere degradation across animal life. Evaluation of telomeres with respect to aging has also been conducted in pigs and horses, and there are fewer reports of telomere biology in beef cattle, sheep, and goats. There were minimal associations of telomere length with animal productivity measures. Most, but not all, work in livestock has documented an inverse relationship between peripheral blood cell telomere length and age; that is, a longer telomere length was associated with younger age. Because livestock longevity affects productivity and profitability, the role of tissue-specific telomere attrition in aging may present alternative improvement strategies for genetic improvement while also providing translational biomedical knowledge.