Nitrogen Metabolism of Early Lactation Cows Fed Diets with Two Different Levels of Protein and Different Amino Acid Profiles

摘要: Abstract Four multiparous Holstein cows (569±122kg) surgically prepared with indwelling catheters in the mesenteric, portal, and hepatic veins carotid artery were allocated a 4 × Latin square to determine effects of dietary crude protein (CP) level amino acid (AA) profile on N metabolism during early lactation (from 25 65 d milk). Cows received their diets two equal meals milked twice daily. The treatments were: 18% CP high (18H) or low (18L) quality AA profile, 15% (15H) (15L) profile. four similar net energy for (1.75 NE L Mcal/kg) contained same amount RUP (34% CP). pertained only essential (EAA), was assessed by comparison EAA casein considered potential contribution from ruminal bacteria. 18H 15H supplemented 50 25g/d ruminally protected Met, respectively. After 10 treatment, blood flow marker (p-amino-hippurate) infused into mesenteric vein, arterial, hepatic, mammary samples obtained at 3, 6, 12h after feeding. Dry matter intake across (23.4±0.5kg/d). Amino oxidation, consequent urea production, liver numerically greater rations, and, as result, arterial concentrations greatest ( P =0.16) (47.7 46.3kg/d, respectively) compared 18L 15L (45.9 44.6kg/d, respectively). Also, milk contents =0.09) H diets. Milk plasma