Inbreeding Implications on Genetic Diversity and Population Evolution of South American Brown Swiss Cattle

Inbreeding is a critical issue in both conservation and animal breeding, as it can severely impact survival, reproductive success and genetic diversity (GD) in domestic species. The Brown Swiss cattle were introduced in South America around a century ago; however, the breeding scheme-derived consequences have been neglected by breeders for numerous generations. The present research aimed to elucidate the population evolution, inbreeding and GD in introduced South American Brown Swiss cattle using genealogical databases. The study was based on official registered records from 8686 animals across multiple generations (until 2023). Different estimates related to population structure, including pedigree completeness, inbreeding rate (F), effective population size (Ne) and generation interval (GI), among others, were evaluated. Moreover, the characterisation of the probabilities of gene origin (effective number of founders [fe] and ancestors [fa]) and the GD loss were assessed. The results revealed that in the last period, GMax was 12.33, while the GCom and GEqu were 2.37 and 5.43, respectively. The mean GI was 7.11 years, and the mean F of 1.27% in the historical and the most recent populations was 5.60 and 2.78, respectively. The F increased between 0.10% and 0.50% per chronological period, showing an increasing tendency of the inbreeding values throughout time. The average Ne-census, Ne- ΔF_p and Ne-GEqu were 339.50, 143.80 and 95.40, respectively. Thus, a declining tendency of the effective population size was observed over time. The probabilities of gene-origin-derived traits were 55 and 32 for fe and fa, respectively. The fe/fa ratio in the population was 1.72, indicating that occasional bottlenecks may have occurred in this breed. The GD analysis revealed a loss of 3.35% of total heterozygosity over time, though significant variability exists among chronological periods. In conclusion, this study revealed that considerable GD loss exists within the Brown Swiss cattle population, which needs better management mainly due to the relatively low founder effect and the low number of animals for maintaining a moderate reservoir of population diversity. Finally, these results emphasise the significance of overseeing GD and reducing inbreeding impacts. Successful breeding programmes are vital to improve conservation strategies and long-term sustainable practices in South American Brown Swiss cattle.