Population structure of Lori-Bakhtiari sheep in Iran by pedigree analysis

Abstract

The objective of this study was to describe the population genetic structure and evaluate the state of conservation of genetic variability of Lori-Bakhtiari sheep in Iran. As such, pedigree information of 10,644 lambs lambed from 1989 through 2016 in the stud flock of Lori-Bakhttiari sheep was included in the analysis. Our first goal was to estimate mean and variance of family size across sires and dams using pedigree data. Our second goal was to estimate population structure in Lori-Bakhtiari sheep including estimation of pedigree completeness (PC), genetic conservation index (GCI), effective population size (Ne), effective number of founders (fe), effective number of ancestors (fa), generation interval (L), individual inbreeding coefficient (F) and average relatedness coefficient (AR) using the ENDOG software. The results showed that the average number of progenies per ram and ewe in their lifetime were 26.44 (15–152) and 3.6 (1–15), respectively. The mean and variance of family size of sires differ across years. The pedigree completeness (PC) was equal to 0.61. The fe and fa were 109 and 98, respectively with a ratio of 1.11. The number of ancestors explaining 50% of genetic diversity was 30. The Ne also varied from 142.68 to 144.13 during the study period. The average generation interval was 4.11 years. The mean inbreeding coefficient was 2.5% in inbred lambs and 1.26% in whole population with an annual increase of 0.09% per year and 0.87% per generation. The AR of the total population was estimated to 2.27% with an incremental trend of 0.10% per year and 0.59% in each generation. The average GCI was 11.75 units with an incremental trend of 0.76 per year. The effects of birth type and year of birth were found to be significant on most of the studied demographic parameters. Though there is an increasing inbreeding coefficient trend over a number of generations, it is still lower than the maximum acceptable recommendation of 1% per generation. This provides us an opportunity for maintaining genetic diversity and implementation of the improvement breeding program. However, unbalanced use of rams led to the creation of family size variation over years. Therefore, this study warrants a comprehensive mating plan with minimum inbreeding rate to maintain genetic variability in Lori-Bakhtiari sheep.