ABSTRACT


Claudio Wernli Küpfer1
 
A previous papel (Chapter 1) examined the faetors affeeting the voluntary consumptíon ai sllage. The present knowledge on the two other components of nutriuve value (digestion and efficiency of utilization) is reviewed here, particularly comparíng silage with the original forage fed fresh or conserved as hay or by artilficíal dehydration. The dígestibility of ensiled forages depends mainly on the digestibility of the original crop. The process of forage fermentation during ensiling may significantly influence the digestibility of the ensiled material. This effeet will depend on the characteristies of the fermentation process. Digestibility of the dry matter of silage is often reduced, although the magnitude of this effect is variable. The effect of wilting the forage and the use of additives prior to ensiling upon digestibility of ensilage is not clear and more information is needed to clarify this point. The utilization of energy is a complex process, with several diet and animal factors playing an important role. Information on the efficiency of utilizatian of energy obtained from calorimetric studies or by the comparative slanghter teehnique is limited. Different laboratories have often studied only one or two of the variables involved in the utilization of digestible and metabolizable energy of silage for maintenance and productive purposes, and the results obtained have been variable. From these rectrieted data it is not possible to obtain a complete understanding of the factors which have given rise to the variable results in published experiments.
The nature of rumen fermentation appears not to differ markedly for animals fed silage, fresh forage or hay, and this factor will probably play a less important role on differences in effieiency of utilization of metabolizable energy between types of forage. Differences in mastication activity between these types of feed allows speculation on a possible negative influence by this concept upon the efficiency of utilization of energy in silage.
The efficiency of utilization of nitrogen is generally lower for silage than for hay or the artificially-dehydrated crop. This is partly attributed to the partially degraded condition of the protein and energy fractions in silage. This low utilization of nitrogen appears to be markedly improved by wilting the forage before ensiling. Consideration of the published information reviewed in Chapters I and n leads to the conclusion that the most important limitation to high quality silage as a feed for ruminants is its low voluntary intake. For this reason, the intake of metabolizable energy and retention of nitrogen, as well as levels of animal production, are characteristically low in animals fed silage. It would seem logical, therefore, that most research effort should be placed on the study of the voluntary intake of silage, in an attempt to understand further the factors responsible for this low intake and to develop methods of ensiling or feeding whereby higher levels of comsumption can be achieved. There is also the need to study the use of silage fed in mixed diets, in order to ensure high levels of animal production from diets based on ensiled forage.
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1Ing. Agr., Ph. D., Area Producción Animal, Instituto de Investigaciones Agropecuarias (INIA), Casilla 5427, Santiago, Chile. Profesor Cursos Pregrado y Postgraduados en Producción Animal, Depto. de Producción Animal, Sede Santiago Sur, Unviersidad de Chile.