Effects of energy balance and metabolizable protein level on tissue mobilization and milk performance of dairy cows in early lactation

The objective of this study was to investigate the effect of dietary energy and metabolizable protein supply on feed intake, milk production, blood metabolites and tissue mobilization in dairy cows during the first 14 weeks of lactation. In the experiment, 36 Norwegian Dairy Cattle were used. Three dietary treatments were evaluated, (1) protein and energy supply according to standard recommendations (SS) for amino acids absorbed in the small intestine (AAT) and net energy lactation (NEL), (2) low protein and low energy (LL; 50% of the concentrate energy fed to SS) and (3) high protein (135% of that fed to LL) and low energy (HL). Energy corrected milk (ECM) was not significantly different between SS and HL but both were higher than LL (P<0.05), 4.6 and 2.8 kg higher, respectively. Increased AAT supply at low energy intake increased (P<0.05) ECM, protein yield and stimulated increased mobilization of fat. The latter was verified by higher levels (P<0.05) of non-esterified fatty acids and acetoacetate in blood and acetone in milk. However, increased fat mobilization showed no effect on incidence of ketosis. It is concluded that the AAT supply in early lactation is an important factor in regulating milk yield and milk protein production.