EFFICIENCY OF PROTEIN-UTILIZATION IN DAIRY-COWS

Feed intake, milk production and composition were determined in three experiments (a total of 131 multiparous dairy cows), to measure the ef fect of protein intake on animal performance. A range of 80 to 120% of the estimated requirement for intestinal digestible protein (DVE) rel ative to energy requirement was tested. Diet composition was checked b y chemical analyses, in-vitro digestibility and in-sacco degradation. The individual feed intake, milk production and composition and body w eight changes were recorded for 16 to 20 weeks in early lactation for each animal. Means per week were used for statistical interpretation. Animal performance, milk, protein and lactose production, improved sig nificantly on a higher level of feed intake. A higher DVE intake relat ive to energy intake also improved production. However, multiple regre ssion analyses showed, that the effect of DVE supply in addition to en ergy intake was not significant. The small, marginal effect of extra D VE on protein yield resulted in a significant reduction of the efficie ncy of milk protein synthesis from 78% to almost 50%. Reasons for this reduction and the relationship with the genetic potential of the anim als is discussed.