Genetic Diversity and Trends of Ancestral and New Inbreeding in German Sheep Breeds by Pedigree Data

Abstract

In Germany, many autochthonous sheep breeds have developed, adapted to mountain, heath, moorland, or other marginal sites, but breeds imported from other countries have also contributed to the domestic breeds, particularly improving wool and meat quality. Selective breeding and the intense use of rams may risk losing genetic diversity and increasing rates of inbreeding. On the other hand, breeds with a low number of founder animals and only regional popularity may not leave their endangered status, as the number of breeders interested in the breed is limited. The objective of the present study was to determine demographic measures of genetic diversity and recent as well as ancestral trends of inbreeding in all autochthonous German sheep breeds and sheep of all breeding directions, including wool, meat, and milk. We used pedigree data from 1,435,562 sheep of 35 different breeds and a reference population of 981,093 sheep, born from 2010 to 2020. The mean number of equivalent generations, founders, effective founders, effective ancestors, and effective founder genomes were 5.77, 1669, 123.2, 63.5, and 33.0, respectively. Genetic drift accounted for 69% of the loss of genetic diversity, while loss due to unequal founder contributions was 31%. The mean inbreeding coefficient, individual rate of inbreeding (∆F_i), and realized effective population size across breeds were 0.031, 0.0074, and 91.4, respectively, with a significantly decreasing trend in ∆F_i in 11/35 breeds. New inbreeding, according to Kalinowski, contributed to 71.8% of individual inbreeding, but ancestral inbreeding coefficients showed an increasing trend in all breeds. In conclusion, in our study, all but one of the mountain-stone sheep breeds and the country sheep breed Wald were the most vulnerable populations, with N_e < 50. The next most endangered breeds are exotic, country, and heath breeds, with average N_e of 66, 83, and 89, respectively. The wool, meat, and milk breeds showed the highest genetic diversity, with average N_e of 158, 120, and 111, respectively. The results of our study should help strengthen conservation program efforts for the most endangered sheep breeds and maintain a high genetic diversity in all sheep breeds.

Keywords: German sheep breeds; ancestral inbreeding; genetic diversity; inbreeding; pedigree analysis; realized effective population size.

Figure 1

Boxplots of genealogical estimators of genetic diversity for 35 sheep breeds in Germany with (A) effective number of founders (f_e), (B) effective number of founder genomes (f_g), (C) effective number of ancestors (f_a) and their ratios, and (D–F) representing possible bottlenecks in the population.

Figure 2

Loss of genetic diversity from unequal contributions of founders and genetic drift.

Figure 3

Individual rate of inbreeding (ΔF_i) and realized effective population size (N_e) in 35 sheep breeds.

Figure 4

Inbreeding coefficients of Kalinowski ancestral (F_{a_Kal}) and new (F_New) in 35 sheep breeds.

Figure 5

Ancestral inbreeding coefficients in 35 sheep breeds, according to Ballou (F_{a_Bal}) and Baumung (AHC).

Figure 6

Number of dams (No_dams) and effective number of dams (Effective_dams) as birth year averages for 35 sheep breeds.

Figure 7

Number of sires (No_sires) and effective number of sires (Effective_sires) as birth year averages for 35 sheep breeds.