The A Allele of the Cholecystokinin Type A Receptor Gene g.420 C > A Polymorphism Improves Growth Traits in Amakusa Daioh Cross Chicken

Practical Application of Miyazaki Jitokko Chickens Selected for a Superior Allele at a Single Nucleotide Polymorphism Site in the Cholecystokinin Type A Receptor Gene

This study aimed to examine 1) whether selection for a superior allele at a single nucleotide polymorphism site (SNP; AB604331, g.420 C>A) of the chicken cholecystokinin type A receptor (CCKAR) gene in Miyazaki Jitokko chickens is detectable in commercial poultry farms, and 2) whether the reproductive traits of the Kyushu Rhode hens, as a maternal stock line of the Miyazaki Jitokko chickens, are affected by SNP selection. Conventional and A-allele fixed (improved) Miyazaki Jitokko chicks were hatched on the same day and raised in a battery cage until 7 days of age. The chicks were then deposited at two commercial poultry farms and reared until slaughter at 126 and 163 days for cockerels and pullets, respectively. Body weight on the day of hatching (day 0), at 5 days of age, and at slaughter were measured. The differences in the body weights of the farm and test groups at slaughter were analyzed using the generalized linear model. A-allele fixation increased the body weight at slaughter by approximately +123.5 g and +131.9 g in cockerels and pullets, respectively. No significant differences between the conventional and improved hens were detected in terms of egg-laying rate, fertilization rate, and hatchability in the Kyushu Rhode hens. The data suggest that fattening chicks can be supplied as usual, even if Kyushu Rhode hens are switched from the conventional to improved type. In conclusion, genetic improvements using the CCKAR SNP site as a marker were effectively established in terms of the growth of the Miyazaki Jitokko chickens in commercial farms and the reproductive traits of the Kyushu Rhode hens.

Verification of the Effectiveness of an SNP Marker in the Cholecystokinin Type A Receptor Gene for Improving Growth Traits in Okumino-kojidori Chickens

A significant association was reported between a single nucleotide polymorphism (SNP; AB604331, g.420 C>A) in the cholecystokinin type A receptor gene and growth traits in some Japanese slow-growing chickens. Demonstration tests of the genetic improvement effect by comparing the superior allele-A fixed chickens with conventional ones were carried out considering the effect of different seasons on growth traits in other slow-growing chickens. Meat-type Okumino-kojidori chickens from Gifu Prefecture are a three-way cross of Gifu-jidori improved, White Plymouth Rock, and Rhode Island Red breeds. We used a total of 468 meat-type Okumino-kojidori: 264 individuals from a private hatchery as conventional chickens and 204 A-allele fixed individuals from the Gifu Prefectural Livestock Research Institute as improved chickens. We performed fattening experiments over two seasons: summer and winter. In each season, experimental birds of both sexes were hatched on the same day, raised in the same chicken house, and fed the same diet ad libitum for 12 weeks. Body weight was recorded at 3, 6, 9, and 12 weeks of age. SNP genotypes were determined using the mismatch amplification mutation assay. Association between the SNP and growth traits was analyzed using generalized linear models built on sex-based, seasonal, additive, and dominance genetic effects. The observed AA, AC, and CC genotype frequencies in the conventional chickens were 0.158, 0.479, and 0.363, respectively; body weight at 12 weeks and average daily gain from 3 to 12 weeks was superior for the A allele compared to the C allele. The improved chickens were heavier than the conventional ones at 12 weeks. Body weight at 12 weeks in allele-A fixed chickens increased by 3.2% compared to the conventional chickens. We concluded that g.420 C>A is a good selective marker that increases slaughter weight in the meat-type Okumino-kojidori chickens.

Is a Single Nucleotide Polymorphism Marker in the Cholecystokinin A Receptor Gene Practically Suitable for Improving the Growth Traits of Hinai-jidori Chickens?

We have previously reported a significant association between the single-nucleotide polymorphism (SNP; g.420 C>A) in the cholecystokinin type A receptor gene (CCKAR) and the growth traits of Hinai-dori, a breed of chicken that is indigenous to Japan. Moreover, we have demonstrated that the minor allele of this SNP improved the growth rate in a low-growth line of the Hinai-dori breed. Hence, in the present study, we verified the association between this SNP and the growth traits of the Hinai-jidori chicken: a cross between a Hinai-dori sire and Rhode Island Red dam. In addition, we verified whether the growth rate was improved in Hinai-jidori chickens produced from the parent stocks in which the SNP A/A genotype was fixed by selection (improved Hinai-jidori chickens). The Hinai-jidori female chicks at 4 weeks of age, were subdivided into three genotypic groups (A/A, A/C, and C/C), with 20 chicks in each group, and reared in an open-sided poultry shed until 23 weeks of age. The results showed that the body weight at 23 weeks of age and the average daily gain after 14 weeks of age were significantly higher in group A/A than in group C/C. Subsequently, the improved and the conventional Hinai-jidori chickens were reared until they reached 22 weeks of age to verify the effects on their growth traits. The body weight of the improved Hinai-jidori chickens at 22 weeks was significantly greater than the conventional Hinai-jidori chickens. Moreover, the association between the SNP and body weights of Hinai-jidori chickens at market age (24 weeks) on the production farms showed that the A allele was significantly superior to the C allele. In conclusion, the CCKAR g.420 C>A SNP improves the growth rate of commercial Hinai-jidori chickens and could be a candidate marker for improving the growth performance in selective breeding of Hinai-jidori chickens.

Effect of a Single Nucleotide Polymorphism in the Cholecystokinin Type A Receptor Gene on Growth Traits of the Miyazaki Jitokko Chicken

The Miyazaki Jitokko chicken, native to the Miyazaki Prefecture in southern Kyushu Island, Japan, is the product of a three-way cross involving the Jitokko, White Plymouth Rock, and Kyushu Rhode breeds. In the present study, associations between a single nucleotide polymorphism (SNP; AB604331, g.420 C>A) of the chicken cholecystokinin type A receptor gene and growth traits in Miyazaki Jitokko chickens were investigated. Unrelated male birds (n=120) that had hatched on the same day were raised in the same chicken house and fed the same diet ad libitum from day 0 to 17 weeks of age. Body weight was recorded at 0, 1, 2, 3, 4, 5, 7, 9, 11, 13, 15, and 17 weeks and the average daily gain of each interval was calculated from the body weight data. SNP genotyping of each bird was performed using the mismatch amplification mutation assay. The associations between the SNP and growth traits were examined using the Thesias program. The genotype frequencies of AA, AC, and CC were 0.525, 0.383, and 0.092, respectively. AA birds were significantly heavier than CC birds from 4 to 17 weeks of age. In the estimated effect of alleles, body weight from 1 to 17 weeks of age in birds with the A allele was greater than that in birds with the C allele. During the rearing period, the effect of the A allele on average daily gain in the first half was greater than that in the second half. We conclude that the g.420 C>A SNP can be used as a selection marker for the parent stock lines of the Miyazaki Jitokko chickens to increase their growth performance.