MODELING WEATHER EFFECTS ON NUTRITIONAL-VALUE OF GRASS-CLOVER LEYS .1. ESTIMATION AND VALIDATION OF PARAMETERS IN A MODEL FOR CHANGES IN METABOLIZABLE ENERGY CONTENT

A model for weather affected change in nutritional value of forage is presented. Two parameters that determine the shape of the change rate function of metabolizable energy content (ME) were optimized by means of data from field experiments obtained during 1985-1988 at six sites in central and southern Sweden. The 2-step optimization procedure was tested by comparison of observed and simulated values of ME content an d expressed as the root mean square error of prediction (RMSP). As a r esult of the optimization, common values of sites, years and nitrogen levels for both parameters could be fitted for each species and growin g period. This implies that ME prediction could be made without field sampling.