Energy efficiency and its relationship with milk, body, and intake traits and energy status among primiparous Nordic Red dairy cattle.

Existing variation in energy efficiency and its relationship with milk yield and milk composition, body weight and body condition, feed intake, and energy status was studied in primiparous Nordic Red dairy cattle with data including 3,752 weekly records from 145 cows. Energy efficiency was defined as energy conversion efficiency (ECE) and as residual energy intake (REI) estimated based on Finnish feeding standards (REI₁) or from the current data (REI₂). The results indicated true phenotypic variation in energy efficiency of the cows. The proportion of total variance due to the animal was 0.35 for REI₁, 0.30 for REI₂, and 0.50 for ECE. The high efficiency based on ECE was associated with increased mobilization of body reserves (r = -0.50) and decreased dry matter intake (r = -0.51). With REI as an energy efficiency measure, the increased efficiency was associated with a large decrease in feed intake (REI₁: r = 0.60; REI2: r = 0.74) without any effect on body weight change (REI₁: r = 0.13; REI2: r = 0.00). Increased efficiency based on ECE and REI₁ was associated with increased milk yield (ECE: r = 0.58; REI₁: r = -0.41). A clear effect of stage of lactation on REI was found, which could be caused by true differences in utilization of metabolizable energy during lactation. However, it might also be related, in part, to the lack of knowledge of the composition of body weight change in the beginning of lactation.