Forty years of captive breeding in Przewalski's horse: pedigree‐based insights into population growth, sex ratio, and inbreeding

Long‐term captive breeding programs play a critical role in the conservation and reintroduction of endangered species, yet they face persistent challenges related to demographic structure and genetic management. The Przewalski's horse Equus przewalskii , once extinct in the wild, represents a global model for conservation breeding supported by pedigree‐based management. Here, we analyzed pedigree records from the Xinjiang Wild Horse Breeding Center (WHBC), the world's largest captive breeding facility for the species, covering the period from 1985 to 2023. Using demographic analyses and generalized linear models, we examined long‐term trends in foaling output, first‐year foal survival, sex ratio, maternal age at reproduction, founder contribution, and inbreeding. A total of 428 foals were born during the study period, of which 372 survived to at least one year of age. Foal survival was positively associated with maternal parity. In contrast, foal survival probability declined over time and was negatively associated with individual inbreeding coefficient, suggesting cumulative genetic and demographic constraints in this semi‐closed population. Reproductive output was highly skewed among founders, with four males accounting for more than 90% of surviving descendants sired by founding males. Maternal reproductive age increased significantly over time, reflecting progressive aging of the breeding population. Offspring sex ratio was associated with maternal age, with mares in their prime reproductive years (5–14 years) producing a higher proportion of male offspring. Management‐driven removal of older and younger females through release and transfer further influenced demographic structure and sex‐ratio dynamics. Our results demonstrate that while pedigree‐informed management has supported population persistence and large‐scale reintroduction, emerging challenges – including demographic aging, skewed founder representation, and increasing inbreeding – pose risks to long‐term sustainability. These findings highlight the need for introducing new genetic lineages and integrating pedigree data with molecular genetic tools to optimize future conservation breeding and reintroduction strategies for Przewalski's horse and other endangered ungulates.