[1]State Key Laboratory of Animal Nutrition Beijing Engineering Technology Research Center of Raw Milk Quality and Safety Control College of Animal Science and Technology China Agricultural University Beijing 100193 People’s Republic of China;
[2]Faculty of Agriculture Department of Animal Science Lorestan University PO Box 465 Khorramabad Iran;
High-altitude pulmonary hypertension; Holstein heifers; N-carbamylglutamate; Tibet;