Influence of substrate and aerobic exposure on chemical composition and the metabolome of silages and on the preference behavior of ruminants
Final Report Abstract
Silage volatile organic compounds (VOC) can have a negative, neutral, or sometimes positive influence on silage preference and intake in ruminants. We have reviewed and evaluated the literature on (1) formation of silage VOC and (2) effects of silage VOC on ruminant feeding behavior and have discussed various mechanisms of action and magnitude of the impact of VOC, such as acetic acid (AcA), propionic acid (PrA), butyric acid (BtA), ethanol, esters, and propanol, on ruminant feeding behavior. During the process of ensiling, several fermentation compounds are formed, which also include VOC. The precise knowledge on the formation of non-routinely measured VOC such as aldehydes, esters, and ketones is very scant. Studies that analyzed the synthesis and occurrence of aldehydes, esters, and ketones, and their respective influence on feed preference and DMI showed conflicting results. Accordingly, determining the occurrence and the concentrations of less studied VOC may help to reveal their relationship with DMI. To date, no comprehensive review has highlighted the formation of major and minor silage VOC. Therefore, we provide extensive and up to date information on the major and minor VOC that are formed in silages and their effect on silage quality. Although it is known that fermentation products or VOC reduce dry matter intake (DMI), the significance of each compound is still unclear. Due to the complex silo environment and the concurrent formation of different fermentation products or VOC, an error-free relationship between a specific compound and DMI may not be possible with silage DMI models. Testing a specific VOC on preference and DMI in feeding trials can provide a better picture than infusion studies because the former method can check for both sensory and post-ingestive factors that influence preference and DMI. It seems that the simultaneous presence of high concentrations of different VOC reduced preference and DMI more than a single compound. Among VOC, AcA, and PrA seem to have more hypophagic effects than others. However, in many studies the negative effect of AcA and PrA on DMI was not observed. These compounds can obviously offset their drawbacks in some cases. For instance, aerobic spoilage can be reduced by the presence of AcA and PrA in silage. Although anecdotal evidence suggests that alcohols and esters can reduce preference and DMI, the addition of these substances in preference and feeding trials did not show negative effects. Other VOC, such as BtA, ethanol, esters, methanol, propanol, iso-BtA, and iso-valeric acid, seem to have no negative influence on preference or DMI. Metabolomic studies revealed that thousands of metabolites, among which many are VOC, can be found in silage. Future experiments that employ metabolomic analysis, in addition to routine chemical analysis, may have the potential to reveal other unidentified VOC that can impact silage preference and intake.
Publications
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Silage volatile organic compounds and ruminant feeding behavior – a review. Proc. Soc. Nutr. Physiol. 31, 94
Bandla, N., Südekum, K.-H. & Gerlach, K.
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Review: Role of silage volatile organic compounds in influencing forage choice behavior and intake in ruminants. Animal Feed Science and Technology, 307, 115853.
Bandla, Naveen; Südekum, Karl-Heinz & Gerlach, Katrin
