Manman Shen

Genetic parameters of feed efficiency traits in laying period of chickens

Laying records on 1,534 F2 hens, derived from a reciprocal cross between White Leghorns and Dongxiang blue-shelled chickens, were used to estimate genetic parameters for residual feed intake (RFI), feed conversion ratio (FCR), daily feed intake (FI), metabolic BW (MBW), BW gain (BWG), and daily egg mass (EM) at 37 to 40 (T1) and 57 to 60 wk age (T2), respectively. Genetic analysis was subsequently conducted with the AI-REML method using an animal model. Estimates for heritability of RFI, FCR, and FI were 0.21, 0.19, and 0.20 in T1, and 0.29, 0.13, and 0.26 in T2, respectively. In T1 and T2, RFI showed high and positive genetic correlations with FCR (0.51, 0.43) and FI (0.72, 0.84), whereas the genetic correlation between FI and FCR was very low (−0.09, 0.11). Genetically, negative correlations were found between RFI and its component traits (−0.01 to −0.47). In addition, high genetic correlations, from 0.76 to 0.94, were observed between T1 and T2 for RFI, FCR, and FI, suggesting that feed efficiency traits in the 2 stages had a similar genetic background. The results indicate that selection for low RFI could reduce FI without significant changes in EM, while selection on FCR will increase EM. The present study lays the foundation for genetic improvement of feed efficiency during the laying period of chickens.

Genome-Wide Association Studies for Comb Traits in Chickens

The comb, as a secondary sexual character, is an important trait in chicken. Indicators of comb length (CL), comb height (CH), and comb weight (CW) are often selected in production. DNA-based marker-assisted selection could help chicken breeders to accelerate genetic improvement for comb or related economic characters by early selection. Although a number of quantitative trait loci (QTL) and candidate genes have been identified with advances in molecular genetics, candidate genes underlying comb traits are limited. The aim of the study was to use genome-wide association (GWA) studies by 600 K Affymetrix chicken SNP arrays to detect genes that are related to comb, using an F2 resource population. For all comb characters, comb exhibited high SNP-based heritability estimates (0.61–0.69). Chromosome 1 explained 20.80% genetic variance, while chromosome 4 explained 6.89%. Independent univariate genome-wide screens for each character identified 127, 197, and 268 novel significant SNPs with CL, CH, and CW, respectively. Three candidate genes, VPS36, AR, and WNT11B, were determined to have a plausible function in all comb characters. These genes are important to the initiation of follicle development, gonadal growth, and dermal development, respectively. The current study provides the first GWA analysis for comb traits. Identification of the genetic basis as well as promising candidate genes will help us understand the underlying genetic architecture of comb development and has practical significance in breeding programs for the selection of comb as an index for sexual maturity or reproduction.

Genetic architecture dissection by genome-wide association analysis reveals avian eggshell ultrastructure traits

The ultrastructure of an eggshell is considered the major determinant of eggshell quality, which has biological and economic significance for the avian and poultry industries. However, the interrelationships and genome-wide architecture of eggshell ultrastructure remain to be elucidated. Herein, we measured eggshell thickness (EST), effective layer thickness (ET), mammillary layer thickness (MT), and mammillary density (MD) and conducted genome-wide association studies in 927 F2 hens. The SNP-based heritabilities of eggshell ultrastructure traits were estimated to be 0.39, 0.36, 0.17 and 0.19 for EST, ET, MT and MD, respectively, and a total of 719, 784, 1 and 10 genome-wide significant SNPs were associated with EST, ET, MT and MD, respectively. ABCC9, ITPR2, KCNJ8 and WNK1, which are involved in ion transport, were suggested to be the key genes regulating EST and ET. ITM2C and KNDC1 likely affect MT and MD, respectively. Additionally, there were linear relationships between the chromosome lengths and the variance explained per chromosome for EST (R2 = 0.57) and ET (R2 = 0.67). In conclusion, the interrelationships and genetic architecture of eggshell ultrastructure traits revealed in this study are valuable for our understanding of the avian eggshell and contribute to research on a variety of other calcified shells.

Comparison of dynamic change of egg selenium deposition after feeding sodium selenite or selenium-enriched yeast

ABSTRACT The aim of this study was to compare the dynamic change of egg selenium (Se) deposition after sodium selenite (SS) or selenium‐enriched yeast (SY) supplementation for 1, 3, 5, 7, 14, 21, 28, 56, and 84 d. A total of 576 32‐wk‐old Hy‐Line Brown laying hens were randomly assigned to 3 groups (192 laying hens per group) with 6 replicates, and fed a basal diet (without Se supplementation) or basal diets with 0.3 mg/kg of Se from SS or 0.3 mg/kg of Se from SY, respectively. The results showed that the Se concentrations in the eggs from hens fed a SY‐supplemented diet were significantly higher (P < 0.001) than those from hens fed a SS‐supplemented diet or a basal diet after 3 d. And the Se concentrations in the eggs from hens fed a SS‐supplemented diet were significantly higher (P < 0.001) than those from hens fed a basal diet after 14 d. There was a positive linear and quadratic correlation between Se concentrations in the eggs from hens fed a SY‐supplemented diet (r2 = 0.782, P < 0.001; r2 = 0.837, P < 0.001) or SS‐supplemented diet (r2 = 0.355, P < 0.001; r2 = 0.413, P < 0.001) and number of feeding days. The Se concentrations in the breasts from hens fed a SY‐supplemented diet were 126.98% higher (P < 0.001) than those from hens fed a SS‐supplemented diet, and were 299.44% higher (P < 0.001) than those from hens fed a basal diet after the 84‐d feeding period. In conclusion, the dietary Se was gradually transferred into eggs with the extension of the experimental duration. The deposition rate of Se in the eggs from hens fed a SY‐supplemented diet was much more rapid than that from hens fed a SS‐supplemented diet, and the organic Se from SY had higher bioavailability as compared to inorganic Se from SS.

Genome-wide association studies for small intestine length in an F2 population of chickens

Abstract Small intestine length is an important physiological index that is effected by nutrient intake and thus plays roles in growth and egg-laying in chickens. Although there are some studies about small intestine length, little information is available regarding the genetic architecture of small intestine. The current study was conducted to investigate the genetic architecture of small intestine length. A total of 1435 F2 hens from a White Leghorn and Dongxiang reciprocal cross were phenotyped for the duodenum lengths (DL), jejunum length (JL) and ileum length (IL), and genotyped using a chicken 600 K single nucleotide polymorphism (SNP) genotyping array. SNP-based heritability estimation was performed by SAS algorithm and univariate genome-wide association studies (GWAS) were performed by GEMMA, a genome-wide efficient mixed-model association algorithm. The JL and IL exhibited high SNP-based heritability estimation (0.43 and 0.49, respectively), while the heritability estimation was moderate for the DL (0.36). Three independent univariate genome-wide screens for these small intestine lengths identified 202, 298 and 119 SNPs that were significantly associated with the DL, JL and IL, respectively. The significant genomic regions indicated that ∼170 Mb on GGA1 is an important region for these small intestine lengths. In this region, 78 SNPs were associated with them, of which 4 were involved in cell proliferation and development, corresponding to RB1 (rs313207223), CKAP2 (rs312737959) and SIAH3 (rs312771221, rs15494052) genes. Small intestine length exhibited good SNP-based heritability estimation and the GWAS results indicated that an important genomic region was located on GGA1.

Genetic architecture and candidate genes detected for chicken internal organ weight with a 600 K SNP array

Objective Internal organs indirectly affect economic performance and well-being of animals. Study of internal organs during later layer period will allow full utilization of layer hens. Hence, we conducted a genome-wide association study (GWAS) to identify potential quantitative trait loci or genes that potentially contribute to internal organ weight. Methods A total of 1,512 chickens originating from White Leghorn and Dongxiang Blue-Shelled chickens were genotyped using high-density Affymetrix 600 K single nucleotide polymorphism (SNP) array. We conducted a GWAS, linkage disequilibrium analysis, and heritability estimated based on SNP information by using GEMMA, Haploview and GCTA software. Results Our results displayed that internal organ weights show moderate to high (0.283 to 0.640) heritability. Variance partitioned across chromosomes and chromosome lengths had a linear relationship for liver weight and gizzard weight (R2 = 0.493, 0.753). A total of 23 highly significant SNPs that associated with all internal organ weights were mainly located on Gallus gallus autosome (GGA) 1 and GGA4. Six SNPs on GGA2 affected heart weight. After the final analysis, five top SNPs were in or near genes 5-Hydroxytryptamine receptor 2A, general transcription factor IIF polypeptide 2, WD repeat and FYVE domain containing 2, non-SMC condensin I complex subunit G, and sonic hedgehog, which were considered as candidate genes having a pervasive role in internal organ weights. Conclusion Our findings provide an understanding of the underlying genetic architecture of internal organs and are beneficial in the selection of chickens.

Genetic architecture of bone quality variation in layer chickens revealed by a genome-wide association study

Skeletal problems in layer chickens are gaining attention due to animal welfare and economic losses in the egg industry. The genetic improvement of bone traits has been proposed as a potential solution to these issues; however, genetic architecture is not well understood. We conducted a genome-wide association study (GWAS) on bone quality using a sample of 1534 hens genotyped with a 600 K Chicken Genotyping Array. Using a linear mixed model approach, a novel locus close to GSG1L, associated with femur bone mineral density (BMD), was uncovered in this study. In addition, nine SNPs in genes were associated with bone quality. Three of these genes, RANKL, ADAMTS and SOST, were known to be associated with osteoporosis in humans, which makes them good candidate genes for osteoporosis in chickens. Genomic partitioning analysis supports the fact that common variants contribute to the variations of bone quality. We have identified several strong candidate genes and genomic regions associated with bone traits measured in end-of-lay cage layers, which accounted for 1.3–7.7% of the phenotypic variance. These SNPs could provide the relevant information to help elucidate which genes affect bone quality in chicken.

Genetic Architecture and Candidate Genes Identified for Follicle Number in Chicken

Follicular development has a major impact on reproductive performance. Most previous researchers focused on molecular mechanisms of follicular development. The genetic architecture underlying the number of follicle, however, has yet not to be thoroughly defined in chicken. Here we report a genome-wide association study for the genetic architecture determining the numbers of follicles in a large F2 resource population. The results showed heritability were low to moderate (0.05–0.28) for number of pre-ovulatory follicles (POF), small yellow follicles (SYF) and atresia follicles (AF). The highly significant SNPs associated with SYF were mainly located on GGA17 and GGA28. Only four significant SNPs were identified for POF on GGA1. The variance partitioned across chromosomes and chromosome lengths had a linear relationship for SYF (R2 = 0.58). The enriched genes created by the closest correspondent significant SNPs were found to be involved in biological pathways related to cell proliferation, cell cycle and cell survival. Two promising candidate genes, AMH and RGS3, were suggested to be prognostic biomarkers for SYF. In conclusion, this study offers the first evidence of genetic variance and positional candidate genes which influence the number of SYF in chicken. These identified informative SNPs may facilitate selection for an improved reproductive performance of laying hens.

Safety evaluation of daidzein in laying hens: Effects on laying performance, hatchability, egg quality, clinical blood parameters, and organ development

&NA; Daidzein has become increasingly popular as a dietary supplement, particularly for postpeak‐estrus animals, as a safe and natural alternative estrogen‐like compound. However, there is little available safety data of daidzein in laying hens. A study was conducted to examine if high‐dose daidzein affected the safety of hens, including mortality, laying performance, egg quality, hematological parameters, clinical chemical parameters, organ development parameters, and hatchability. A total of 2,448 42‐wk‐old Rugao laying hens were randomly assigned to 4 groups with 6 replicates of 102 birds each (612 laying hens per group). After a 2‐wk acclimation period, the birds were fed diets supplemented with 0, 10, 100, or 200 mg/kg of daidzein for 12 wk. The hatchability of setting eggs increased linearly with increasing dietary daidzein supplementation (P = 0.034), while the hatchability of fertile eggs also tended to increase linearly (P = 0.069). The red cell distribution width (RCDW) and coefficient variation of RCDW showed an increasing and then decreasing quadratic response to increasing dietary daidzein supplementation (P = 0.001 and 0.002, respectively). No statistically significant changes were observed in mortality, laying performance, egg quality, clinical chemistry parameters, or organ development parameters (P > 0.05). The magnitude of these hematological changes was such that they were considered to be of no toxicological significance. Therefore, a nominal daidzein concentration of 200 mg/kg is not expected to cause adverse effects following daily administration to laying hens for 84 d.

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.