Energy and nitrogen balance of dairy cattle as affected by provision of different essential amino acid profiles at the same metabolizable protein supply.

Amino acid composition of metabolizable protein (MP) is important in dairy cattle diets, but effects of AA imbalances on energy and N utilization are unclear. This study determined the effect of different AA profiles within a constant supplemental MP level on whole-body energy and N partitioning in dairy cattle. Five rumen-fistulated Holstein-Friesian dairy cows (2.8 ± 0.4 lactations; 81 ± 11 d in milk; mean ± standard deviation) were randomly assigned to a 5 × 5 Latin square design in which each experimental period consisted of 5 d of continuous abomasal infusion followed by 2 d of rest. A total mixed ration consisting of 58% corn silage, 16% alfalfa hay, and 26% concentrate (dry matter basis) was formulated to meet 100 and 83% of net energy and MP requirements, respectively, and was fed at 90% of ad libitum intake by individual cow. Abomasal infusion treatments were saline (SAL) or 562 g/d of essential AA delivered in 4 profiles where individual AA content corresponded to their relative content in casein. The profiles were (1) a complete essential amino acid mixture (EAAC), (2) Ile, Leu, and Val (ILV), (3) His, Ile, Leu, Met, Phe, Trp, Val (GR1+ILV), and (4) Arg, His, Lys, Met, Phe, Thr, Trp (GR1+ALT). The experiment was conducted in climate respiration chambers to determine energy and N balance in conjunction with milk production and composition, digestibility, and plasma constituents. Compared with SAL, infusion of EAAC increased milk, protein, and lactose yield, increased energy retained as body protein, and did not affect milk N efficiency. Total N intake and urine N output was higher with all AA infusions relative to SAL. Compared with EAAC, infusions of GR1+ILV and GR1+ALT produced the same milk yield and the same yield and content of milk fat, protein, and lactose, and had similar energy and N retention. Milk N efficiency was not different between EAAC and GR1+ILV, but was lower with GR1+ALT compared with EAAC, and tended to be lower with GR1+ALT compared with GR1+ILV. Infusion of ILV tended to decrease dry matter intake compared with the other AA infusions. Milk production and composition was not different between ILV and SAL. Compared with EAAC, infusion of ILV decreased or tended to decrease milk, protein, and lactose yields and milk protein content, and increased milk fat and lactose content. Milk N efficiency decreased with ILV compared with SAL, EAAC, and GR1+ILV. Milk urea concentration was not affected by essential amino acid (EAA) infusions. Plasma urea concentration did not differ between EAAC and SAL, tended to increase with ILV and GR1+ILV over SAL, and increased with GR1+ALT compared with EAAC and SAL. In conclusion, removing Arg, Lys, and Thr or removing Ile, Leu, and Val from a complete EAA profile when the total amount of EAA infused remained constant did not impair milk production, but milk N efficiency decreased when Ile, Leu, and Val were absent. Infusion of only Ile, Leu, and Val decreased milk protein yield and content and reduced milk N efficiency compared with a complete EAA profile.