Blood leukocyte telomere length dynamics in the first year of life in Thoroughbred horses

Telomeres maintain genomic integrity, shortening with ageing and influenced by environmental factors. Informed interpretation requires understanding normal telomere length (TL) dynamics at different stages of life. Although lengthening can occur, attrition rate has been demonstrated in numerous species to be greatest during high growth periods, slowing with maturation. TL dynamics have not been investigated during rapid growth in horses. It was hypothesised that TL dynamics differ between young, rapidly growing horses and adult horses. Venous blood was collected from Thoroughbred mare-foal dyads ( n = 34) from one farm every three months from birth for 12 months. DNA was extracted from blood leukocytes and relative TL (RTL) assessed by RT-qPCR. Linear mixed models were fitted with covariates (foal sex, birth weight, dam/sire age, maternal care style [MCS]) with post-hoc analysis. Foal RTL increased at three ( p = 0.040) and 12 months of age ( p = 0.003) compared to birth. Mare RTL did not change between timepoints. Foal RTL at birth was not associated with mare RTL. None of the covariates influenced foal RTL while high MCS mares had significantly higher RTL values than low MCS mares ( p = 0.021). These results demonstrate that telomere lengthening occurred in this group of rapidly growing horses.