NEWS NOTES

Does Inbreeding Increase Pregnancy Losses?

Breeding choices are critical for Thoroughbreds, according to a recent study that found inbreeding may predispose the mare to mid- and late-term pregnancy losses.

Excessive inbreeding increases the probability of homozygous recessive genotypes and has been associated with an increased risk for retained placenta and lower semen quality in horses, according to the researchers, but to their knowledge no genomic analysis has investigated the association between inbreeding and pregnancy loss.

They compared the genetic inbreeding coefficients (F) of naturally occurring early, mid- and late-term pregnancy losses of Thoroughbred mares with controls. They genotyped allantochorion and fetal DNA from early pregnancy loss (n = 37, gestation age 14–65 days); mid- and late-term (n = 94, gestational age 70 days–24 hours post parturition) and controls (n = 58). Inbreeding coefficients using runs of homozygosity (FROH) were calculated. They split the ROHs into size categories to investigate the recency of inbreeding.

Mid- and late-term pregnancy losses had significantly higher median number of ROH, length of ROH and total number of ROH and FROH when compared with the controls and the early pregnancy losses (P<0.05). There was no significant difference in any of the inbreeding indices between the early pregnancy loss and controls. The mid- and late-term losses had a significantly higher proportion of long (>10 Mb) ROH than the Controls (P = 0.001). No unique ROHs were found among the mares with the early or midand late-term losses. MeV

For more information:

Lawson, NJ, Shilton CA, Lindsay-McGee V, et al. Does inbreeding contribute to pregnancy loss in Thoroughbred horses? Equine Vet J. 2024 Jan. 14. https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.14057