Biology Reference
In-Depth Information
30.1
Introduction
The number of functional teats (FTNUM) in sows affects piglet survival and
reproductive efficiency that, in technical terms, is measured by the number of
piglets weaned per sow per year. The number of teats is a discontinuous, multifac-
torial trait with medium-low heritability (Nicholas
1998
). The Italian Large White
pig breed (ITLW) was selected for FTNUM using thresholds, and only pigs with at
least 14 functional and accessible teats (regularly spaced, well protruded, and with
normal and functional nipples) are registered in the breed Herd Book (maintained
by the National Association of Pig Breeders, ANAS;
http://www.anas.it
). Marker-
assisted selection (MAS) could be an important tool for genetic improvement of
FTNUM (Buske et al.
2006
). At present, 74 quantitative trait loci (QTL) for the
number of teats have been reported, indicating a polygenic influence on this trait
(PigQTL Database;
http://www.genome.iastate.edu/cgi-bin/QTLdb/SS/summary
;
release of April 14, 2010). Considering that litter size is the most important
reproductive trait in sows, it might be interesting to analyze whether alleles in
candidate genes can be used as markers to improve FTNUM. The aim of this study
was to evaluate association between polymorphisms within five genes and FTNUM
in ITLW.
30.2 Materials and Methods
Hair samples were collected from 1,112 ITLW sows from five farms located in the
Emilia-Romagna and Lombardy regions. The samples were used for genomic DNA
extraction and genotyping of five single-nucleotide polymorphisms (SNPs) within
five different genes. Table
30.1
reports information about the targeted genes and the
analyzed SNPs. The genotyping was performed using the Sequenom Iplex
™
GOLD Platform system. A total of 5,215 genotypes were generated (Table
30.2
).
To check the quality of the results, approximately 2% of the samples were analyzed
in duplicate, and Hardy-Weinberg equilibrium was verified by chi-square test.
FTNUM was determined through visual inspection. This information was provided
by ANAS that records this trait for all ITLW animals registered in the Herd Book.
The sows were categorized into two groups based on their FTNUM (1) sows with
14 teats (minimum requested by the Herd topic) and (2) sows with more than 14
teats. For each polymorphism, differences in allele and genotype frequencies
between the two groups of sows were tested using the FREQ procedure of SAS
(version 9.2). To reduce the possibility of type I errors (false positives), nominal P
values were corrected for multiple testing using the Bonferroni correction.
