Growth hormone is a positive regulator of mammary gland development.Dairy animals that are administered growth hormone display enhanced lactation performance, a desirable agricultural trait.The objective of the current research was to generate an improved milk production phenotype in a large animal model using overexpressed GH in the mammary gland to enhance mammary development.To this end, we constructed a mammary gland-specific expression vector, pcGH, and demonstrated effective GH expression in goat mammary epithelial cells in vitro by ELISA.To produce transgenic offspring that were capable of stable GH expression in vivo, the linearized pcGH vector was electroporated into goat fetal fibroblasts.Cell colonies that were positive for GH were used as donors for nuclear transfer to enucleated oocytes.A total of 253 morulae or blastocytes developed from the reconstructed embryos were transferred to 56 recipients, resulting in 24 pregnancies at day 35.Finally, six transgenic goats were born.PCR and southern blotting detection confirmed the success of the cloning procedure.To observe the development of dairy goats, the six dairy goats were mated with a completely healthy ram, and four became pregnant.In the later pregnancy period, the size of the udders of the transgenic goats was bigger than normal goats.These experiments indicated that the pcGH vector was incorporated into the transgenic goats and affected mammary gland growth, which laid a solid foundation for elucidating the impact of GH on lactation performance and mammary gland development.