The EIA was carried out directly in 100 μL of yak plasma. The sensitivity of EIA procedure was 20 pg/well GH, which corresponds to0.2 ng/mL plasma For the biological validation of assay, 2 mature yaks were administered (10 μg, iv) with a synthetic analogue of GHRH and blood samples were collected at 15-min interval using indwelling jugular catheter beginning 2 h prior to GHRH injection till 8 h thereafter.