The Z chromosome of the silkworm contains a major gene that influences silk yield. This major locus on chromosome Z accounts for 35.10% of the phenotypic variance. The location and identification of the gene have been a focus of silkworm genetics research. Unfortunately, identification of this gene has been difficult. We used extreme phenotype subpopulations and selected from a backcross population, BC 1 M, which was obtained using the high-yield strain 872B and the low-yield strain IS-Dazao as parents, for mapping the gene on the chromosome Z. The candidate region was narrowed down to 134 kb at the tip of the chromosome. BmAbl1 in this region correlated with silk gland development by spatiotemporal expression analysis. This gene was differentially expressed in the posterior silk glands of the high-and low-yield strains. In BmAbl1, an insertion-deletion (indel) within the 10th exonic region and an SNP within the 6th intronic region were detected and shown to be associated with cocoon shell weight in 84 Bombyx mori strains with different yields. Nucleotide diversity analysis of BmAbl1 and its 50 kb flanking regions indicated that BmAbl1 has experienced strong artificial selection during silkworm domestication. This study is the first to identify the genes controlling silk yield in the major QTL of the Z chromosome using forward genetics.

This study was conducted to evaluate the influence of supplementing tea polyphenols (TP) in diet of laying hens on yolk cholesterol content and production performance. A total of 1800 Lohmann laying hens aged 48 weeks were randomly allocated to 6 groups. Each group consisted of 6 replicates with 50 layers. The feeding experiment was 4 weeks including one-week acclimatization. Layers fed basal diet supplemented with 0, 150, 200, 250, 300 and 350 mg TP/kg diet, respectively. The results showed that average daily feed intake (ADFI), feed conversion ratio (FCR), average egg weight (AEW), laying rate and the indicators of egg quality were not significantly affected by the diet supplemented with 300 mg/kg TP (p>0.05). However, yolk cholesterol content decreased by increasing TP concentration (p<0.01), with 18.06% reduction in layers fed diet supplemented with 300 mg TP/kg. Also, the diet supplemented with 300 mg/kg TP significantly decreased plasma triglyceride (TG), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) level (p<0.05). The activity of serum glutathione peroxidase (GSH-Px) was enhanced by increasing TP concentration, while the content of serum methane dicarboxylic aldehyde (MDA) was decreased by increasing TP concentration. The highest activity of GSH-Px and the lowest serum MDA content were both determined in 300 mg/kg TP group (p<0.01). In conclusion, this study suggests that the addition of 300 mg TP/kg basal diet had no negative effect on the production performance laying hens, yet decreased the egg yolk cholesterol content and enhanced the antioxidant capacity of laying hens at the same time.