Analysis of Ancestral Inbreeding Across Main Founders and Ancestors in the Polish Simmental Cattle Population.

This study estimated the impact of main founders and ancestors on inbreeding subdivision in the Polish Simmental cattle population. Two reference populations were defined: subset A (20,827 cows born 1984-2009) and subset B (19,554 cows born 2010-2020). Ancestral inbreeding coefficients were calculated relative to the main founders and ancestors for all cows in both subsets. Significant changes in ancestor composition were observed in younger cows. The main founders with the highest genetic contribution numbered 10 in subset A and 7 in subset B, with 7 common to both. Main ancestors numbered 11 (all bulls) in subset A and 15 in subset B, with 6 shared between subsets. The frequency of occurrence of common founders in subset B ranged from 42% to 49%, while that of common ancestors ranged from 31% to 68%. Kalinowski's new inbreeding coefficient was six times higher in subset B than in subset A. Although overall inbreeding levels remained low, the proportion of cows with elevated inbreeding increased over time despite continuous importation of breeding animals. These findings suggest that breeders should scrutinize more carefully the pedigrees of imported animals to prevent further inbreeding accumulation.