The metabolisable energy requirement for maintenance and the efficiency of use of metabolisable energy for lactation and tissue gain in dairy cows offered a straw/concentrate ration

Data from a series of 36 complete energy balance trials (determined by indirect calorimetry) with eight high genetic merit lactating Holstein Friesian cows offered a straw/concentrate ration (0.18:0.82 dry matter basis) were analysed by a range of regression techniques to determine the metabolisable energy (ME) required for maintenance (MEm), and the efficiencies of ME use for lactation (k(1),) and concomitant tissue gain (k(g)). In the data set, milk yield ranged from 1.0 to 37.2 kg/day (s.d. 10.56), with this achieved by stage of lactation, plane of nutrition and drying off two quarters of all animals. Mean MIE, was determined as 0.61 MJ/kg(0.75) per day (range 0.60-0.62) which was proportionately 0.27 above the value predicted from Agricultural and Food Research Council (AFRC, 1990) (0.48 MJ/kg0.75). It is suggested that ME, is influenced by animal genotype or body condition, which can both reflect differences in fat and protein contents of the body. The mean k(1), value produced was 0.59, which is above that (0.51) calculated:From the relationship k(1), = E-I(0)/MEp when the latter is calculated using the MEm predicted from AFRC (1990). The mean derived value of k(g), 0.86, has limited biological meaning considering the small portion of total energy use on which the estimate is based. (C) 1999 Elsevier Science B.V. All rights reserved.