Assessment of genomic selection for introgression of polledness into Holstein Friesian cattle by simulation

Abstract

a b s t r a c tNaturally hornless cattle are called polled. The possibility to introgress the allele responsible (P) for polledness in a cattle population that is more intensively selected for other traits is investigated in this paper. Gene introgression, generally carried out by several steps of backcrossing and selection, takes a long time and may lead to unacceptable genetic loss in other traits or inbreeding. The main objective of the current study was to evaluate the use of genomic selection to speed up the introgression of a target allele in a conventional dairy cattle breeding scheme with overlapping generations. A cattle population and a breeding program were simulated and run over a 12 year selection period. Assuming that the polled population was inferior for overall genetic merit , two selection strategies were evaluated: i) selection on conventional BLUP-EBV (CBLUP); ii) selection on genomic EBV (GEBV) obtained with the genomic relationship matrix used in BLUP (GBLUP). Both selection strategies were applied with (PSEL) and without (NOP-SEL) selection for the single polled locus (P). The overall level of genetic merit, the P allele frequency and the inbreeding level (F) in the new born animals were monitored each year, as well as the average genetic gain per year of selection (ΔG). The overall genetic level of new born animals was higher for GBLUP compared to CBLUP, with an average ΔG/year of 8.34% (GBLUP) against 7.49% (CBLUP). The PSEL scenario reduced genetic gain, but P allele frequency increased from 0.130 to 0.415 (CBLUP) and from 0.128 to 0.440 (GBLUP) for PSEL, after 12 years of selection. No substantial changes in allele frequency were recorded for NOPSEL scenarios, both for CBLUP and GBLUP breeding schemes. The overall inbreeding rates for GBLUP were 0.28%/y (NOPSEL) and 0.30%/y (PSEL) and for CBLUP 0.52%/ y (NOPSEL) and 0.44%/y (PSEL). In conclusion, application of GS to gene introgression helped to speed up the process of introgression of a gene while simultaneously increasing the genetic gain and reducing the inbreeding rate.

The effectiveness of genomic selection for milk production traits of Holstein dairy cattle

“…When selected for the milk yield using GEBV, the genetic gain increased in this study by about 7.1% over the gain with the EBV method in cows with test records, and by 2.9% in bulls with progeny records, while it increased by about 24.2% in heifers without test records and by 35% in young bulls without progeny records. Therefore, the application of genomic selection to gene introgression can help to speed up the process of introgression of a gene while simultaneously increasing the genetic gain [3].…”

“…With the development of DNA analysis technology and the reduced cost of single nucleotide polymorphism (SNP) chip analysis, a lot of research has been conducted on the genomic selection of dairy cattle [1][2][3][4][5][6][7]. Gengler et al [8] proposed an algorithm that could predict genomic information about individuals without genomic information, and VanRaden [9] developed methods to calculate the genomic relationship matrix and to estimate the genomic estimated breeding value (GEBV).…”

Breeding for polledness in Holstein cattle

“…This corresponds to the result of about 5 years of selection in the Holstein bulls (difference between top 100 bulls in 2009 and 2014 is 139). Clearly the use of genomic selection has accelerated the genetic gain, and breeding values of polled bulls have benefited from the use of genomic selection (compare Gaspa et al, 2015). Not only the breeding values have increased but the number of polled bulls available for AI has increased as well, including homozygous polled bulls with high genetic merit.…”

Simultaneous introgression of three POLLED mutations into a synthetic breed of Chinese cattle

“…In order to breed a stable polled population in Shuxuan cattle, therefore, the direct selection based on phenotype or even on the genotype would take a long time or result into considerable genetic loss because the polledness trait is inherited in the dominant manner. Fortunately, a recent study first proposed that approach of genomic selection could speed up the selection progress of polled population [ 26 ], which could be applied to Shuxuan cattle in the future.…”