Genetic Connectedness Between Norwegian White Sheep and New Zealand Composite Sheep Populations With Similar Development History

Theodorus Meuwissen,Natalie Pickering,Luiz F Brito,Shannon Marie Clarke,Thor Blichfeldt,Jette Jakobsen,Hinayah Rojas Oliveira,John Colin Mcewan

doi:10.3389/fgene.2020.00371

Abstract

The Norwegian White sheep (NWS) and New Zealand Terminal Sire Composite (NZC) sheep breeds have been developed based on crossing of multiple breeds, mainly of Northern European origin. A close genetic relationship between these populations could enable across-country genomic evaluations. The main objectives of this study were to assess the genetic connectedness between Norwegian and New Zealand sheep populations and estimate numerous genetic diversity metrics for these two populations. A total of 792 NWS and 16,912 NZC animals were genotyped using a high-density Illumina SNP chip panel (∼606K SNPs). The NZC animals were grouped based on their breed composition as: Finn, Lamb Supreme, Primera, Texel, “Other Dual Purpose”, and “Other Terminal Sire”. The average level of linkage disequilibrium ranged from 0.156 (for Primera) to 0.231 (for Finn). The lowest consistency of gametic phase was estimated between NWS and Finn (0.397), and between NWS and Texel (0.443), respectively. Similar consistency of gametic phase was estimated between NWS and the other NZC populations (∼ 0.52). For all composite sheep populations analyzed in this study, the majority of runs of homozygosity (ROH) segments identified had short length (<2,500 kb), indicating ancient (instead of recent) inbreeding. The variation in the number of ROH segments observed in the NWS was similar to the variation observed in Primera and Lamb Supreme. There was no clear discrimination between NWS and NZC based on the first few principal components. In addition, based on admixture analyses, there seems to be a significant overlap of the ancestral populations that contributed to the development of both NWS and NZC. There were no evident signatures of selection in these populations, which might be due to recent crossbreeding. In conclusion, the NWS composite breed was shown to be moderately related to NZC populations, especially Primera and Lamb Supreme. The findings reported here indicate a promising opportunity for collaborative genomic analyses involving NWS and NZC sheep populations.

Highlights

MATERIALS AND METHODSThe Norwegian White Sheep (NWS) is a composite breed that accounts for 70–75% of the total Norwegian sheep population
The average distances between adjacent single nucleotide polymorphisms (SNP) were similar across populations and ranged from 0.023 Mb (NWS, “Other Dual Purpose”, Lamb Supreme, and “Other Terminal Sire”) to 0.025 Mb (Finn)
Among all New Zealand Terminal Sire Composite (NZC) populations, “Other Dual Purpose” and “Other Terminal Sire” Composites presented the most similar average linkage disequilibrium (LD) compared to NWS (∼ 0.17)

Summary

Introduction

The Norwegian White Sheep (NWS) is a composite breed that accounts for 70–75% of the total Norwegian sheep population. This breed is well known for its prolificacy and high growth rates. Three distinct breeds Dala, Rygja and Steigar highly influenced by the imports were formed in the first half of the 20th century. Crossing between these three breeds along with imported Texel and Finn sheep took place in the second half of the 20th century. The composite NWS was officially formed in 2000 including all aforementioned breeds. The NWS breeding program is well organized and has resulted in substantial annual genetic progress for growth and carcass yield, reduced subcutaneous fat, and increased litter size and milking ability (NSG, 2019)

Objectives

Results

Conclusion