Genome‐wide identification of runs of homozygosity islands in the Gyr breed ( Bos indicus )

Runs of homozygosity and signatures of selection for number of oocytes and embryos in the Gir Indicine cattle

Runs of homozygosity (ROH) and signatures of selection are the results of selection processes in livestock species that have been shown to affect several traits in cattle. The aim of the current work was to verify the profile of ROH and inbreeding depression in the number of total (TO) and viable oocytes (VO) and the number of embryos (EMBR) in Gir Indicine cattle. In addition, we aim to identify signatures of selection, genes, and enriched regions between Gir subpopulations sorted by breeding value for these traits. The genotype file contained 2093 animals and 420,718 SNP markers. Breeding values used to sort Gir animals were previously obtained. ROH and signature of selection analyses were performed using PLINK software, followed by ROH-based (F_ROH) and pedigree-based inbreeding (F_ped) and a search for genes and their functions. An average of 50 ± 8.59 ROHs were found per animal. ROHs were separated into classes according to size, ranging from 1 to 2 Mb (ROH_1-2Mb: 58.17%), representing ancient inbreeding, ROH_2-4Mb (22.74%), ROH_4-8Mb (11.34%), ROH_8-16Mb (5.51%), and ROH_>16Mb (2.24%). Combining our results, we conclude that the increase in general F_ROH and F_ped significantly decreases TO and VO; however, in different chromosomes traits can increase or decrease with F_ROH. In the analysis for signatures of selection, we identified 15 genes from 47 significant genomic regions, indicating differences in populations with high and low breeding value for the three traits.

Genomic breed composition of pure registered Brazilian Gir

INTRODUCTION

Gir is a Bos indicus breed originally from India, first imported to Brazil in 1850. High-performance Dairy Gir has been systematically selected in Brazil from its arrival. Since the major phenotypic difference between Gir in India and Brazil is a higher milk production in the former, it is speculated that Brazilian Gir was strategically crossed with Holstein or another Bos taurus to improve milk yield. This study evaluated the purity of Brazilian Gir breed stocks from BASA Farms in Brazil, trying to identify possible admixture events with other cattle breeds based on DNA analysis.

MATERIALS AND METHODS

The population included 1061 pure registered individuals genotyped using two commercial platforms with 37 k and 25 k SNPs. Admixture analysis was performed individually to estimate levels of genomic composition derived from six different reference populations, three indicine and three taurine breeds.

RESULTS

A Gir ancestry of 99% or higher was found for 94.2% of the population, while the remaining showed levels of non-Gir ancestry up to 6.8%. Only five individuals were identified with possible taurine ancestry, all of them exhibiting levels lower than 2%. The remaining non-Gir ancestry identified was derived from indicine breeds. The levels of admixture observed in the population were from low to non-detectable. No consistent patterns of admixture were observed indicating sustained introgression of taurine lines as means of genetic improvement.

CONCLUSION

According to these results, genetic improvement achieved by Brazilian Gir breeders is the result of within-breed selection methods applied intensively over the past five decades, rather than the result from sustained introgression.

Identification of Runs of Homozygosity Islands and Genomic Estimated Inbreeding Values in Caqueteño Creole Cattle (Colombia)

The Caqueteño Creole (CAQ) is a native breed of cattle from the Caquetá department (Colombia), adapted to tropical conditions, which is extremely important to production systems in those regions. However, CAQ is poorly studied. In this sense, population structure studies associated with runs of homozygosity (ROH) analysis would allow for a better understanding of CAQ. Through ROH analysis, it is possible to reveal genetic relationships between individuals, measure genome inbreeding levels, and identify regions associated with traits of economic interest. Samples from a CAQ population (n = 127) were genotyped with the Bovine HD BeadChip (777,000 SNPs) and analyzed with the PLINK 1.9 program to estimate FROH and ROH islands. We highlighted a decrease in inbreeding frequency for FROH 4−8 Mb, 8−16 Mb, and >16 Mb classes, indicating inbreeding control in recent matings. We also found genomic hotspot regions on chromosomes 3, 5, 6, 8, 16, 20, and 22, where chromosome 20 harbored four hotspots. Genes in those regions were associated with fertility and immunity traits, muscle development, and environmental resistance, which may be present in the CAQ breed due to natural selection. This indicates potential for production systems in tropical regions. However, further studies are necessary to elucidate the CAQ production objective.

Assessing the accuracy of imputation in the Gyr breed using different SNP panels

The aim of this study was to evaluate the accuracy of imputation in a Gyr population using two medium-density panels (Bos taurus - Bos indicus) and to test whether the inclusion of the Nellore breed increases the imputation accuracy in the Gyr population. The database consisted of 289 Gyr females from Brazil genotyped with the GGP Bovine LDv4 chip containing 30 000 SNPs and 158 Gyr females from Colombia genotyped with the GGP indicus chip containing 35 000 SNPs. A customized chip was created that contained the information of 9109 SNPs (9K) to test the imputation accuracy in Gyr populations; 604 Nellore animals with information of LD SNPs tested in the scenarios were included in the reference population. Four scenarios were tested: LD9K_30KGIR, LD9K_35INDGIR, LD9K_30KGIR_NEL, and LD9K_35INDGIR_NEL. Principal component analysis (PCA) was computed for the genomic matrix and sample-specific imputation accuracies were calculated using Pearson's correlation (CS) and the concordance rate (CR) for imputed genotypes. The results of PCA of the Colombian and Brazilian Gyr populations demonstrated the genomic relationship between the two populations. The CS and CR ranged from 0.88 to 0.94 and from 0.93 to 0.96, respectively. Among the scenarios tested, the highest CS (0.94) was observed for the LD9K_30KGIR scenario. The present results highlight the importance of the choice of chip for imputation in the Gyr breed. However, the variation in SNPs may reduce the imputation accuracy even when the chip of the Bos indicus subspecies is used.

The Identification of Runs of Homozygosity Gives a Focus on the Genetic Diversity and Adaptation of the "Charolais de Cuba" Cattle

Simple Summary

The Charolais de Cuba cattle is a tropical adapted breed founded in Cuba around 120 years ago from Charolais French specimens. Nowadays, it is still a closed breed and remains as a small population. In this work, we analyzed the inbreeding and diversity patterns, as well as the population size, of this recent adapted breed via a run of homozygosity (ROH) analysis. We found that the genomic inbreeding levels are higher in the Charolais de Cuba breed compared to French and British Charolais populations. Nevertheless, we detected that the effective population size experienced a very similar decline during the last century in the three Charolais populations studied. Finally, a number of regions with exceptional patterns of long homozygosity were identified in this breed, and these could be related to processes of adaptation to tropical conditions.

Abstract

Inbreeding and effective population size (Ne) are fundamental indicators for the management and conservation of genetic diversity in populations. Genomic inbreeding gives accurate estimates of inbreeding, and the Ne determines the rate of the loss of genetic variation. The objective of this work was to study the distribution of runs of homozygosity (ROHs) in order to estimate genomic inbreeding (F_ROH) and an effective population size using 38,789 Single Nucleotide Polymorphisms (SNPs) from the Illumina Bovine 50K BeadChip in 86 samples from populations of Charolais de Cuba (n = 40) cattle and to compare this information with French (n = 20) and British Charolais (n = 26) populations. In the Cuban, French, and British Charolais populations, the average estimated genomic inbreeding values using the F_ROH statistics were 5.7%, 3.4%, and 4%, respectively. The dispersion measured by variation coefficient was high at 43.9%, 37.0%, and 54.2%, respectively. The effective population size experienced a very similar decline during the last century in Charolais de Cuba (from 139 to 23 individuals), in French Charolais (from 142 to 12), and in British Charolais (from 145 to 14) for the ~20 last generations. However, the high variability found in the ROH indicators and F_ROH reveals an opportunity for maintaining the genetic diversity of this breed with an adequate mating strategy, which can be favored with the use of molecular markers. Moreover, the detected ROH were compared to previous results obtained on the detection of signatures of selection in the same breed. Some of the observed signatures were confirmed by the ROHs, emphasizing the process of adaptation to tropical climate experienced by the Charolais de Cuba population.