Somatostatin (SST) and its receptors (SSTR1-5) appear to be important in central regulation of many metabolic systems that affect growth, adiposity and nutrient absorption. In this study, we investigated polymorphisms within the caprine SST and SSTR1 genes and determined their relationship with growth traits. As there were no sequence information of the caprine SST and SSTR1 genes, we explored their DNA sequence and genomic organizations. The caprine SST gene is organized in two exons and is transcribed into an mRNA containing 351 bp of sequence coding for a protein of 116 amino acids. Its protein sequences showed substantial similarity (97-99%) to its respective orthologs from cattle, human and mouse. We also cloned and sequenced a 1.2 kb DNA fragment which contained the major part of the coding region and 3' UTR of the caprine SSTR1 gene. We then detected the polymorphisms in these determined sequences by PCR-SSCP and DNA sequencing methods in 459 goats from four breeds. Four SNPs (GU014693:g.647T>C, GU014693:g.844A>C, GU014693:g.970T>C, GU014693:g.1039T>A), segregating as two haplotypes (T-A-T-T and C-C-C-A), were identified in intron 1 of the caprine SST gene and showed the associations to body length and body height (P < 0.05). Two SNPs (GU014695:g.801 C>T, GU014695:g.948 C>T) were identified in the caprine SSTR1 gene. Significant associations between the three genotypes of GU014695:801 C>T and body length, body height, and chest circumference was observed (P < 0.05). These results suggest that the caprine SST and SSTR1 genes are strong candidate genes that influence growth traits in goat.

The vascular endothelial growth factor (VEGF) is a regulator of angiogenesis which is an important physiological adaptation to increased metabolic demand. Thus, mutations of this gene may exert a significant influence on animal growth. We screened the exons of the caprine VEGF gene using PCR-SSCP and DNA sequencing methods in 459 individuals from four goat breeds to identify sequence variations that may have an effect on protein structure and function, and might be related to different phenotypes of growth traits. Two single nucleotide polymorphisms (SNPs) (GU014696:g.49 G>C and GU014696:g.270G>A) were identified in the P3 locus of the caprine VEGF gene. Significant associations were observed between the genotypes of the P3 locus and body length, body height and chest circumference. Individuals with genotype P3-B had a significantly longer body length and higher body height than individuals containing genotype P3-AB. Thus, animals of genotype P3-AB should be culled in a selection programme for fast growth. It is suggested that P3-B could be used as a molecular marker in marker-assisted selection (MAS).

Animal lysozymes, which have been studied in many of invertebrate and vertebrate species, have been characterized and demonstrated to be immune-associated molecules, digestive enzymes and multifunctional molecules. The purpose of this study was to detect the connection between lysozyme-gene polymorphism and the production traits of a Chinese native chicken breed (Langshan chicken). Four single nucleotide mutation sites were identified: G345A, C1726T, G1836A, A1838G. By the linkage disequilibrium analysis, six haplotypes and 15haplotype combinations were depicted in the studied population. The statistical analysis demonstrated that the SNPs and the haplotype combinations are related to body weight at sixteen weeks of age in Langshan chickens (p<0.05), and those with combined haplotype Hap3-Hap6 (GA-TT-GG-AA) presented higher body weight. Our study demonstrated that the SNPs and their haplotype combinations in the lysozyme gene were associated with the chicken production traits, and that SNPs can be used as a molecular marker for chicken marker-assisted selection.