Evaluation of the NEL system and estimation of energy requirements for dairy cows on the basis of extensive data set from feeding trials | Bewertung des NEL-system und Schätzung des Energiebedarfs von Milchkühen auf der Basis eines Umfangreichen Datenmaterials als Fütterungsversuchen in Deutschland, Österreich und in der Schweiz

The maintenance requirements of dairy cows are assumed to be about 0.293 - 0.350 MJ NEL/kg LW0.75 in most of the recent energy systems established in Europe and USA. The utilisation of ME for milk production (kl) is in the range of 0.60 - 0.63 in these systems. Recent research results from Northern Ireland indicate both a higher maintenance require-ment and a higher energetic efficiency for milk production. A comprehensive data set obtained from long term feeding experiments with lactating dairy cows carried out in 9 research institutes of Germany, Austria and Switzerland was used to evaluate the current German feeding standards (GfE 2001). The NEL system was validated by regressing the NEL requirements calculated on the basis of its assumptions on the actual NEL intakes (MJ). ME requirements were estimated using multiple regression analysis with LW0.75 (live weight), LE (lactation energy), and LWC (live weight change) as independent variables. The validation of the NEL system is described by the following equation and shows high individual deviations from the regression line, leading to low R SQ: NE requirement calculated = 24.1 + 0.83 × NE intake (1) R SQ = 0.660, MSPE = 316, MPE = 17.8 MJ NEL and 14.7 %, respectively. Components of MSPE: Bias = 3.7%, Line = 10.9%, Random = 85.4%. The estimation of the ME requirement is described by the following equation: ME intake = 0.652 × LW0.75 + 1.41 × LE + 16.6 × LWC (2) R SQ = 0.717, RSD = 24.1 MJ The results reveal a considerable higher maintenance energy requirement than used in current energy systems, but are in line with recent observations in experiments carried out in Northern Ireland; the coefficient of energetic efficiency for lactation is higher than in current systems (kl = 1/1.41 = 0.71) as well. The higher kl value could be due to an increased proportion of ruminally undegraded nutrients in actual feed rations resulting in decreased microbial fermentation losses and a relatively lower chewing activity in low forage diets. The equation gives a much lower energy content for mobilisation/retention of body reserves (ELWC = 16.6 × 0.71 = 11.8 MJ) than usually expected. Besides, the relationship between LWC and energy balance is not significant. Actually, LWC cannot be regarded as a useful predictor of energy balance. Both an increased internal organ mass associated with higher feed intake and a higher protein content (lower BCS) of high yielding dairy cows could be possible reasons for the enhanced maintenance energy requirement. It is concluded that recent data from feeding trials provide evidence that current NE systems for lactating dairy cows underestimate the energy requirement for maintenance and overestimate the energy requirement for lactation.