Mapping of quantitative trait loci affecting growth traits in a Japanese native chicken cross.(Report)

INTRODUCTION

In poultry, many QTL mapping studies have been performed on breed crosses, e.g. broiler x layer (Sewalem et al., 2002), Red Junglefowl x White Leghorn (Kerje et al., 2003), White Leghorn x Rhode Island Red (Sasaki et al., 2004), and broiler x White Leghorn (Schreiweis et al., 2005). This approach has proved very successful in identifying QTLs that explain differences between these breeds; however, they provide no insight into whether these QTLs would be useful for breeds/lines other than the founder breeds used in the respective QTL studies. Therefore, studies using crosses between divergently selected lines within a breed are becoming popular for their potential contribution to the improvement of growth traits in broilers (Jacobsson et al., 2005; Ankra-Badu et al., 2009; Wahlberg et al., 2009) and eggshell traits in the White Leghorn (Takahashi et al., 2009, 2010; Yang et al., 2010). Moreover, there are few studies that described QTLs for growth traits within a native chicken breed.

The Hinai-dori is a slow-growing breed of chicken native to Akita Prefecture, in northern Honshu Island, Japan. Although Hinai-dori meat has a characteristic taste and the breed has been used for a long time, it has decreased in numbers in recent times owing to the introduction of exotic breeds, and for a while was at risk of extinction. The Hinaidori breed has been conserved by hobbyists who belong to the Preservation Society (PS) of the Hinai-dori Breed and is now mainly used for exhibition purposes. For effective use of the breed, selection experiments have been performed at the Livestock Experiment Station (LES), Akita Prefectural Agriculture, Forestry, and Fisheries Research Center (since 1973 when fertilized eggs were introduced to LES from PS) with a view towards increasing growth performance. At present, the average body weight of LES males at 300 days of age is approximately 1 kg heavier than that of PS males. [F.sub.1] chickens produced by crossing the improved LES Hinaidori sires with Rhode Island Red dams have been commercialized as the Hinai-jidori chicken, which is one of the most popular high-quality chickens on the Japanese market. The LES line was developed from PS chickens: hence, these individuals possessed genes that influence growth traits. In order to effectively detect QTLs affecting growth traits within the Hinai-dori breed, we developed an [F.sub.2] resource population by crossing PS sires with LES dams, and thereafter conducted QTL mapping.

MATERIALS AND METHODS

[F.sub.2] resource population

[F.sub.1] chickens were produced by crossing three PS males with nine LES females, with one to three females randomly selected to mate with each male. The mapping population consisted of 359 [F.sub.2] individuals comprising 173 males and 186 females. The [F.sub.2] individuals were produced by full-sib mating of 17 F1 males and 60 [F.sub.1] females. The [F.sub.2] chickens were hatched on the same day, raised in the same chicken house, and fed the same diet ad libitum for the duration of the experiment. Body weight was measured at day 0 (BW-0), 4 weeks (BW-4 wk), 10 weeks (BW-10 wk), and 14 weeks (BW-14 wk) of age. Average daily gain between 0 and 4 weeks of age (ADG 0-4 wk), between 4 and 10 weeks of age (ADG 4-10 wk), and between 10 and 14 weeks of age (ADG 10-14 wk) was calculated from BW at each week of age.

Genotyping and QTL mapping

Chicken genomic DNA was extracted from blood using a DNA isolation kit (SepaGene, Sanko Junyaku, Tokyo, Japan). PCR amplifications were performed in a 6 [micro]l reaction volume, which included 2.5 pmols of each primer, 200 [micro]M each dNTP, 1.2 mM MgSO4, 0.125 units of KOD plus polymerase (KOD-201, Toyobo, Tokyo, Japan), 1x reaction buffer provided by the supplier and 30 ng genomic DNA in a 384-well plate on an iCycler Thermal Cycler (Bio-Rad …