A review of losses arising during conservation of grass forage: Part 2, storage losses

Abstract

Information from the literature about hay and silage storage losses has been reviewed, compared and analysed. An attempt has been made to summarize the information in terms of relationships, suitable for incorporation in an operational research model of forage conservation. Hay storage losses are low and can be related solely to moisture content. In contrast, silage storage losses are much larger, often 20% or more, and the subject is complex. Silage storage losses have been subdivided according to the mechanism by which they arise into fermentation loss, air infiltration losses and effluent loss. Air infiltration losses arise when silos are filled, during the storage period, and while feeding out, and consist of both invisible losses through oxidation of nutrients, and silage which is visibly spoilt due to serious oxidation or overheating so it is unusable. Experimental and modelling studies on the processes of fermentation of silage, air infiltration to silage, and the resulting losses, are discussed. Air infiltration losses are related to density and chop length, and information about values of these factors is also reviewed. From this information, a table of typical loss values has been assembled in relation to dry matter content, chop length, grass maturity, and the use of additives. These represent the best currently available average figures, bearing in mind some uncertainties and inconsistencies in the source material. However, for the forage conservation model, a long-term aim has been identified, namely, to express losses by values estimated from models of the physical processes, which are just now being developed. Information about effluent loss was consistent across a number of sources; it could be summarized as a simple relationship between percentage loss and dry matter content.