Satoshi Mikawa, Takashi Awata

Animal Genome Research Unit

［Abstract］

We identified a novel gene, VRTN, responsible for the number of vertebrae in commercial breeds for pork production. An efficient method for genetic testing of VRTN was also developed to facilitate not only the improvement of meat productivity but also control of meat quality.

［Keywords］

pig, number of vertebrae, genetic testing, livestock industry

［Background］

The number of vertebrae in pigs varies and is associated with body size, which affects meat productivity and reproductive performances. The number of vertebrae also affects indirectly some traits involved in growth and fat deposition. Wild boars have 19 vertebrae, but European commercial breeds for pork production have 20 to 23 vertebrae. Elucidating the responsible gene is therefore expected to contribute in the improvement of meat productivity and meat quality. We have identified the gene associated to the number of vertebrae by a map-based cloning strategy and developed a genetic testing method using the gene sequence information.

［Results and Discussion］

1. We have identified a novel gene, VRTN, associated to the number of vertebrae in commercial breeds. In the number-increase type (Q) allele, no amino acid substitution was observed but seven DNA polymorphisms were detected in the regulatory region. The expression of Q allele was increased in embryonic developmental stages as compared to the wild type (wt) allele. One Q allele increased the vertebral number by an average of 0.63 (Fig. 1, Table 1).
2. We have also developed a genetic testing method to determine the alleles. The genotypes can be judged easily and correctly with general PCR amplification using sequence-specific primers and agarose electrophoresis. Without treatment of restriction enzymes, four bands specific to each of the Q and wt alleles could be detected (Fig 1).
3. In pigs with the Q/Q genotype, the loin was elongated with increased amount of meat in loin and rib parts despite a slightly smaller loin area. Intramuscular fat (IMF) content of loin became larger and cooking loss was minimal due to improved water holding capacity. The meat share value, an index of toughness, also became smaller indicating that the meat became softer (Table 2).
4. In a demonstration experiment in a pig farm, artificial insemination using Q/Q type of semen resulted in pigs with elongated loin, enlarged IMF content and decreased share value. Usage of Q/Q and Q/ wt semen improved the market grading of pork carcasses. (Fig. 2). On the other hand, usage of wt/wt type semen increased the carcasses with excessive backfat.

1. The control of the sires’ genotypes of VRTN improved carcass uniformity and market value. Further improvement in the long term is expected by controlling the genotypes of the dams.
2. The wild type of sires can be used for breeding of enlarged loin area or reduced IMF content.
3. The role of the Q allele in increasing the IMF content and reducing the share values is still unknown. Further studies on the anatomy such as muscle fiber types or thickness are therefore necessary.

Fig.1. Genetic testing of VRTN. By using 15 primers, seven polymorphism sites were judged. Four bands specific to each of the wt and Q allele were detected.

Table 1. Association of the VRTN genotype and the vertebral number

Table 2. Association of the VRTN genotype and carcass traits

Fig. 2. Meat quality evaluation and carcass grading in a demonstration experiment. The pigs used in this study were produced by artificial insemination with the VRTN genotype-judged semen. The genotypes of the dams were unknown. The significance between a and b is p<0.01.

 

[Reference]

1. Mikawa S, Sato S, Nii M, Morizumi T, Imaeda N, Yamaguchi T, Awata T (2011) Identification of a second gene associated with variation in vertebral number in domestic pigs BMC Genetics 12:5