EFFICIENCY OF ENERGY-UTILIZATION IN CATTLE GIVEN FOOD AD-LIBITUM - PREDICTIONS ACCORDING TO THE ARC SYSTEM AND PRACTICAL CONSEQUENCES

Overall efficiency of energy utilization (i.e. total net energy intake as a fraction of metabolizable energy intake) in cattle given food ad libitum was calculated from information included in the United Kingdo m energy evaluation system as published by the Agricultural Research C ouncil. For growing cattle (live weight 250 kg), overall efficiency wa s estimated for five levels of diet metabolizability (ranging from q = 0.45 to q = 0.65) for each of two diet types: coarse/long roughage an d fine/pelleted diets. The overall efficiencies varied from 0.58 to 0. 62 and were not systematically affected by diet type or diet metaboliz ability. For lactating cattle (live weight 600 kg), overall efficiency was also calculated for five diets with metabolizability ranging from 0.45 to 0.65. Calculations were made for cows at equilibrium intake ( i.e. zero energy balance) and at milk production levels proportionatel y 0.30 higher or lower than those attained at equilibrium intake. Over all efficiencies varied from 0.60 to 0.63 and were not systematically affected by diet metabolizability. It is concluded that, in practical cattle production systems with ad libitum feeding, the net energy cont ent of food may be estimated at 0.6 of the metabolizable energy conten t (or 0.5 of the digestible energy content), irrespective of diet type , diet metabolizability or productive function.