Investigation of candidate genes with potential influence on litter size in two commercial pig cross populations
Year: 2006
Type: dissertation
Abstract: Summary English versionThe improvement of desirable traits due to breeding methods in animal farming is still performed by regarding mainly phenotypical selection.Concerning fecundity in swine, this is inefficient and time-consuming due to long generation intervals and high animal numbers, often associated with high costs.However, the improvement of fecundity of sows is of expanding interest for pig producers mainly because improvements concerning feeding regime and housing systems are limited.Furthermore, an improvement of fecundity is also desirable, especially where the achievment potential cannot be exploited because of suboptimal feeding and housing regimes for example in tropical and subtropical regions in order to ensure a sufficient provision of livestock products in the future.Marker assisted selection, employed in conjunction with traditional selection methods is in progress to increase litter size in swine and can accelerate breeding progress.In the past years, researchers began to search for genes underlying reproductive traits in swine.Beside QTLanalyses, in which chromosomal regions can be detected for quantitative traits such as litter size, also the candidate gene approach has been performed by testing one, or several genes directly to associations on fecundity traits.Rothschild et al. (1996) were the first, who published a candidate gene approach with regard to litter size in swine and reported a genetical effect of the estrogen receptor 1 gene (ESR1) for litter size in pigs.Since this time, several candidate genes have been investigated with regard to different fecundity parameters in swine, however, results were often extremely inconsistent.The aim of this thesis was first to evaluate all chromosomal regions (QTL) and candidate genes with association on fecundity in swine, second, to deduce suitable candidate genes and third, to genotype them by using PCR-RFLP methods in order to investigate them for associations to fecundity in two commercial sow populations.As phenotypical trait for fecundity, litter size comprising the total number of born and the number of born alive piglets was chosen according to convenience of its measurement and because of great economical importance of this trait.The selection of candidate genes depended on positional, physiological and comparative aspects.Selected candidate genes were properdin (BF), estrogen receptor 2 (ESR2), glutathione peroxidase 5 (GPX5), fucosyltransferase 1 (FUT1) and cytochrome P450, steroid 21 hydroxylase (CYP21).Two commercial sow populations were used to test the association between gene variants and fecundity.In the first commercial sow farm, 123 out of 447 F 2 -sows with at least four litters were selected with extreme high and extreme low total number born piglets for genotyping (two-tail analysis).The high performance group consisted of 61, wheras the low performance group consisted of 62 sows.In the second commercial sow farm, a total of 129 F 1 -sows with at least four litters were available for the analyses.Evaluation of all published data so far showed that there were 54 QTL, which overlap in part, and 10 candidate genes with association to fecundity parameters in swine, respectively.Fecundity parameters were litter size, ovulation rate, uterine capacity, age of puberty, gestation length and number of nipples.SSC8 and to a lower extent SSC7 and SSC15 are the chromosomes on which most QTL have been found so far.Concerning own results, it can be stated that GPX5 and CYP21 had no effect on litter size in our sow populations.Moderate effects on litter size parameters have been found for the BF and FUT1 genes.However, due to suboptimal animal structures in both commercial sow farms, these results should be considered with caution.For the mutation in exon 5 of the coding region of the ESR2 gene, a significant increase of 0.68 liveborn piglets per sow and litter could be found for the AG genotype in the second sow farm.Due to the pedigree structure, the AA genotype was not detectable.Finally, five novel polymorphisms have been found in the 3' untranslated region of the CYP21 gene by gene sequencing.Most important conclusions are that the improvement of fecundity in swine is one of the most difficult tasks for geneticists as it is determined by several genes due to several chromosomal regions and candidate genes with association to fecundity in swine."Fine mapping" of QTL regions is necessary in order to narrow QTL intervalls and the number of potential positional candidate genes.In order to obtain balanced genotype frequencies, planned matings should be performed for candidate gene approaches in the future.High standardization of environmental parameters is strongly required due to low heritability of litter size.Therefore, working with commercial sow farms is limited for further investigations on genetical influences on fecundity in swine.SSC8, the centromeric region of SSC7 and the ESR2 gene on SSC1 should be considered for further investigations in this field.(GPX5), Fucosyltransferase 1 (FUT1) und Cytochrom P450 Steroid 21 Hydroxylase (CYP21) ausgewählt.Von 447 F 2 -Sauen mit mindestens vier Würfen eines Praxisbetriebes wurden 61 Sauen mit extrem hoher, und 62 Sauen mit extrem niedriger Anzahl insgesamt geborener Ferkel für die Genotypisierung selektiert (two-tail Analyse).Von dem zweiten Praxisbetrieb wurden 129 F 1 -Sauen genotypisiert, welche ebenfalls mindestens vier Würfe aufwiesen.Die Anfertigung der cytogenetischen Karte und die Auswertung der bisher publizierten Ergebnisse ergab 54 zum Teil überlappende QTL und 10 Kandidatengene mit Assoziation zu Fruchtbarkeitsmerkmalen beim Schwein, wie Wurfgröße, Ovulationsrate, Uteruskapazität, Geschlechtsreife, Trächtigkeitsdauer und Anzahl Zitzen.Die meisten QTL wurden bisher auf Chromosom 8 gefunden, ferner sind auch Chromosom 7 und 15 von hervorgehobener Bedeutung.Hinsichtlich der eigenen Ergebnisse konnten für die Gene GPX5 und CYP21 keine, für die Gene BF und FUT1 geringfügige Assoziationen zur Wurfgröße ermittelt werden, welche aber aufgrund des Tiermaterials nicht als zuverlässig betrachtet werden können.Lediglich für die Mutation im codierenden Bereich des ESR2 Gens konnte ein signifikanter Effekt von zusätzlich 0,68 lebend geborenen Ferkel pro Sau und Wurf zugunsten des AG Genotyps in einer Zuchtsauenanlage festgestellt werden.Der AA Genotyp wurde nicht gefunden.Für das Gen CYP21 wurden mittels Gensequenzierung ferner fünf neue SNPs im 3'-Bereich entdeckt.Schlussfolgernd kann gesagt werden, dass, Fruchtbarkeit beim Schwein ein außerordentlich schwieriges, und aufgrund bisher zahlreich gefundener QTL und Kandidatengene ein hochpolygen vererbbares Merkmal ist.Um Chromosomenbereiche und die daraus resultierende Anzahl geeigneter positioneller Kandidatengene für Fruchtbarkeit einzugrenzen, stellt das "Fine mapping" für QTL-Analysen eine vielversprechende Strategie dar.Um balancierte Genotypenfrequenzen zu erhalten, wären Anpaarungstests für Kandidatengenansätze von Vorteil.Ferner ist eine hohe Standardisierung des Tiermaterials aufgrund niedriger Heritabilität von ausschlaggebender Bedeutung.Für weitere Untersuchungen im Hinblick auf Assoziation zu Fruchtbarkeit beim Schwein eignen sich daher Praxisbetriebe nur eingeschränkt.Chromosom 8, die Centromerregion auf Chromosom 7, sowie das ESR2 Gen auf Chromosom 1 sollten bei weiteren Untersuchungen verstärkt berücksichtigt werden.
Source: ORBi (University of Liège)
Author: Bernd Buske
Institutions: University of Liège, Gembloux Agro-Bio Tech
Language: English
Subfield: Genetics
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2240689077