Genetics of litter size and prenatal survival in pigs
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Date
30/06/2012Author
Hernández Velasco, Silvia Clara
Metadata
Abstract
Female reproductive performance is a critical component of sustainable pig
production systems. There is abundant evidence of genetic variation in these traits
among pig breeds. The aims of this study were to identify quantitative trait loci
(QTL) affecting reproductive traits and to identify and characterise positional
candidate gene(s) underlying the QTL. A Large White - Meishan F2 population was
scanned for QTL with effects on reproductive traits. This analysis revealed 13
putative QTLs on seven different chromosomes with effects on five different traits:
ovulation rate (OR), teat number (TN), prenatal survival (PS), total born alive (TBA)
and litter size (LS). QTL for PS and LS on chromosome 8 were fine mapped and
Secreted Phosphoprotein 1 (SPP1) confirmed as a candidate gene. A genome-wide
association study was performed on a diverse population of different breeds and
crosses lines, for reproductive traits including LS, TBA, number of stillborn piglets,
and number of mummified piglets. Fourteen SNPs were found significantly
associated with reproductive traits.
The functional study of SPP1 examined the hypothesis that differences in foetal
growth may be associated with the effectiveness of conceptus attachment, as
measured by SPP1 expression. Patterns of SPP1 mRNA and protein expression in
placental and uterine tissues supplying the smallest and a normal-sized foetus from
the same uterus were examined in Large White-Landrace (LW-LR), Large White
(LW) and Meishan (MS) females 40 and 45 of pregnancy. The smallest LW-LR
foetuses tended to have a higher level of SPP1 mRNA in endometrium tissue
compared to the normal-sized foetuses. However, placenta expression was higher in
the normal-sized foetuses compared to the smallest ones. SPP1 protein levels in
normal sized foetuses were significantly higher than in the smallest litter mates for
all the tissues. Significantly higher levels of SPP1 mRNA and protein were found in
MS compared to LW. In both breeds, significant differences between sizes were
found in some tissues, with similar expression patterns in respect to size, for both
mRNA and protein in endometrial tissues when compared to contemporary LW. In
placenta, the direction of the expression differed between breeds, with a higher
expression of mRNA and protein in the normal-sized MS foetuses and in the smallest sized LW foetuses. The comparison of SPP1 expression between different foetal
sizes and different breeds revealed associations between breed, foetal size, and SPP1
protein, factors implicated in PS and LS. These results together with the genetic
evidence indicate that the potential role of SPP1 in placental and foetal development
merits further investigation.