Association between cholecystokinin type A receptor haplotypes and growth traits in Japanese Hinai-dori crossbred chickens

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.

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

Amakusa Daioh cross chickens are F₁ hybrids of restored Amakusa Daioh sires and Kyushu Rhode dams. In the present study, the association between a single nucleotide polymorphism (SNP; AB604331, g.420 C>A) in the cholecystokinin type A receptor gene and growth traits in Amakusa Daioh cross chicken were investigated. We used 72 male and 72 female birds that had hatched on the same day, were raised in the same chicken house, and were fed the same diet ad libitum from day 0 to 17 weeks (wks) of age. Body weight was recorded at weekly intervals and average daily gain of each week interval was calculated from body weight data. Birds were sacrificed at 17 wks and carcass traits were recorded. SNP genotyping was carried out using the mismatch amplification mutation assay. Associations between the SNP and growth traits were analyzed by a generalized linear model. Body weight from 6 to 17 wks was higher in birds with the A allele than in birds with the C allele, although significant differences in average daily gain traits between birds with A and C alleles were not detected during most of the duration of the experiment. Carcass data showed that birds with the A allele had heavier wings and a smaller proportion of the gizzard than those with the C allele. The g.420 C>A SNP will be useful as a selection marker for parent stock lines to increase the growth performance of Amakusa Daioh cross chickens.

A genome-wide study to identify genes responsible for oviduct development in chickens

Molecular genetic tools provide a method for improving the breeding selection of chickens (Gallus gallus). Although some studies have identified genes affecting egg quality, little is known about the genes responsible for oviduct development. To address this issue, here we used a genome-wide association (GWA) study to detect genes or genomic regions that are related to oviduct development in a chicken F₂ resource population by employing high-density 600 K single-nucleotide polymorphism (SNP) arrays. For oviduct length and weight, which exhibited moderate heritability estimates of 0.35 and 0.39, respectively, chromosome 1 (GGA1) explained 9.45% of the genetic variance, while GGA4 to GGA8 and GGA11 explained over 1% of the variance. Independent univariate genome-wide screens for oviduct length and weight detected 69 significant SNPs on GGA1 and 49 suggestive SNPs on GGA1, GGA4, and GGA8. One hundred and fourteen suggestive SNPs were associated with oviduct length, while 73 SNPs were associated with oviduct weight. The significant genomic regions affecting oviduct weight ranged from 167.79–174.29 Mb on GGA1, 73.16–75.70 Mb on GGA4, and 4.88–4.92 Mb on GGA8. The genes CKAP2, CCKAR, NCAPG, IGFBP3, and GORAB were shown to have potential roles in oviduct development. These genes are involved in cell survival, appetite, and growth control. Our results represent the first GWA analysis of genes controlling oviduct weight and length. The identification of genomic loci and potential candidate genes affecting oviduct development greatly increase our understanding of the genetic basis underlying oviduct development, which could have an impact on the selection of egg quality.

Association between Motilin Receptor Gene Haplotypes and Growth Traits in Japanese Hinai-dori Crossbred Chickens

We previously identified quantitative trait loci (QTL) for body weight and average daily gain in a common region between ADL0198 (chr 1: 171.7 Mb) and ABR0287 (chr 1: 173.4 Mb) on chicken chromosome 1 in an F₂ resource population produced by crossing low- and high-growth lines of the Hinai-dori breed. Motilin receptor (MLNR) is a candidate gene affecting growth traits in the region. In this study, we genotyped polymorphisms of the MLNR gene and investigated its association with growth traits in a Hinai-dori F₂ intercross population. All the exons of the MLNR gene in the parental population were subjected to PCR amplification, nucleotide sequenced and haplotypes identified. To distinguish resultant diplotype individuals in the F₂ population, a mismatch amplification mutation assay was performed. Three haplotypes (Haplotypes 1–3) were accordingly identified. Six genotypes produced by the combination of three haplotypes (Haplotype 1, 2, and 3) were examined in order to identify associations between MLNR haplotypes and growth traits. The data showed that Haplotype 1 was superior to Haplotype 2 and 3 in body weight at 10 and 14 weeks of age, average daily gain between 4 and 10 weeks, 10 and 14 weeks, and 0 and 14 weeks of age in female in F₂ females. It was concluded that MLNR is a useful marker of growth traits and could be used to develop strategies for improving growth traits in the Hinai-dori breed.

Decreased expression of the satiety signal receptor CCKAR is responsible for increased growth and body weight during the domestication of chickens

Animal domestication has resulted in changes in growth and size. It has been suggested that this may have involved selection for differences in appetite. Divergent growth between chickens selected for egg laying or meat production is one such example. The neurons expressing AGRP and POMC in the basal hypothalamus are important components of appetite regulation, as are the satiety feedback pathways that carry information from the intestine, including CCK and its receptor CCKAR (CCK1 receptor). Using 16 generations of a cross between a fast and a relatively slow growing strain of chicken has identified a region on chromosome 4 downstream of the CCKAR gene, which is responsible for up to a 19% difference in body weight at 12 wk of age. Animals possessing the high-growth haplotype at the locus have lower expression of mRNA and immunoreactive CCKAR in the brain, intestine, and exocrine organs, which is correlated with increased levels of orexigenic AGRP in the hypothalamus. Animals with the high-growth haplotype are resistant to the anorectic effect of exogenously administered CCK, suggesting that their satiety set point has been altered. Comparison with traditional breeds shows that the high-growth haplotype has been present in the founders of modern meat-type strains and may have been selected early in domestication. This is the first dissection of the physiological consequences of a genetic locus for a quantitative trait that alters appetite and gives us an insight into the domestication of animals. This will allow elucidation of how differences in appetite occur in birds and also mammals.