ABSTRACT
Summary The aim of this work was to examine the influence of variations in grass management and methods of ensiling on the economics of milk production for autumn-calving cows. A simulation model was developed to combine knowledge of plant and animal responses and their interactions in order to calculate the effects of management options on economic balances. Input data were compiled for herbage production from cutting strategies that gave herbage at four digestibilities, at two levels of applied nitrogen, and in three climates. Experimental evidence was also collated to construct matrices of loss of dry matter and changes in digestibility and intake when herbage of different qualities is ensiled using any combination of the following options at harvest: flail or precision-chop harvester, wilting in the field or not wilting, and using or not using additive. The model combines the herbage-production data with the matrices for ensiling method to give values for the yield and quality of silage produced by each management option (192 combinations in all). A feeding program establishes for each silage the total requirements for silage and supplements of barley and soybean meal for cows achieving potential yield, maximizing silage use, and minimizing the cost of supplements. Margins are calculated for the value of milk minus the cost of supplements and silage in each option. Costs cover any items that vary between options. When herbage yields appropriate to conditions in the UK were used in the model with costs and values current in the 1979-1980 season, greater margins resulted from 350 kg of N/ha than from 150 kg. In comparing cutting strategies, the highest margins/cow were often associated with the use of herbage cut at 66.5 D value (digestible organic matter as a percentage of dry matter), while on the other hand the highest margin/ha of grass came from 61.5 D value. When these margins were expressed/ha of grass plus land for the barley used as supplement, the optimum value for digestibility again rose to 66.5 or 64 D. The effect of digestibility at cutting was less at the high level of applied nitrogen than at the low level. The model enabled factors with critical financial impact to be identified for a particular economic environment. It is of value in considering national strategies, in influencing the direction of future research, and in analyzing problems on a particular farm.
