Factors affecting silage intake.
Ensiling involves the conversion of water-soluble carbohydrates (WSC) to organic acids through the activity of lactic acid bacteria, a process that lowers the pH to preserve the forage. Ensiling has two main advantages: Large quantities of forage are preserved in a short period, and the process is less weather dependent than preserving hay, for instance, or feeding fresh forage daily.
In the past it was believed that ensiling had several disadvantages, including that the changes the crop underwent reduced its potential feeding value and intake as silage. Fact is, silage is a process of loss, and these losses must be managed every step of the way.
Palatability is that property of feed affecting its taste and smell, both of which animals are sensitive to. Palatability may thus be seen as the main culprit when intake-related problems emerge. I believe the correct application of management practices and technology will improve the palatability, digestibility and intake of silage.
Changes and its effect on ensiling
Changes in the nutritional value of forage can be attributed to production procedures, preservation, and postopening management. Forages undergo biochemical and microbiological changes which not only include the rather substantial conversion of WSC to mainly lactic acid, but also the partial breakdown of proteins.
These changes depend on the interaction between micro-organismsText content on the material to be ensiled, and the amount and type of substrate available.
The main factors that can interfere with the fermentation of silage is the dry matter (DM) content, WSC concentration, micro-organism populations present in the forage, and oxygen removal rate.
The fermentation of forages with a low DM and WSC content may be undesirable, while forages with an excessive WSC content may generate acidic silages, which can reduce silage intake.
Due to the fermentation process, many changes occur in the chemical traits of forage. Organic acid concentrations vary, and it is not only these values, but also the relative ratio of certain key organic acids that affect intake.
Some end-products of fermentation, such as high levels of acetic acid, butyric acid (even the smallest of amounts can cause problems), as well as abnormally high levels of ammonia, are associated with reduced silage intake. This is due to poorly fermented, and thus poorly preserved, silage.
Feeding value of silage
The feeding value of silage is usually determined by intake and digestibility, while the quality of silage and the nutrients available have a direct influence on animal performance.
It has long been believed, and often observed, that the intake of silage is generally lower than that of the same forage given fresh. This is attributed, in part, to the presence of toxic substances produced during fermentation.
Yet the validity of a blanket statement such as this should be questioned, as the variability introduced during the production of silage, and management factors during silage production and removal, has a much bigger influence on quality. Proper management can result in well preserved silage and in similar or even greater intakes compared to fresh forage. The correct usage of additives may also increase voluntary intake.
Intake of dry matter
The variation in DM intake has often been blamed on the crop offered to animals as silage. Most documented cases, however, makes very little or no mention of the fermentation traits, different end products of fermentation or management level applicable to each case.
It is not surprising that DM intake is often scrutinised, as it is the main driver of animal performance (60 to 90% of performance-related variations is associated with metabolisable energy intake, and only 10 to 40% with diet digestibility).
Additional benefits
It is sometimes easy to overlook the additional benefits of silage. The fact that an entire crop is harvested at its optimum stage, then fully processed and preserved for a relatively long period, ads to the value of silage when compared to the same crop offered fresh.
We can agree that the fermentation profile of silage can influence palatability, and therefore intake. More precisely, poor fermentation has a negative effect on animals’ intake. However, identifying the origin of the problem, be it the crop or lack of management remains crucial.
