Methods to study the relationship between forage composition and silage fermentation and aerobic stability
Sammanfattning: This thesis is based on the following hypotheses: (I) under controlled ensiling conditions, forage chemical and microbial composition explain variation in silage end-product concentrations (II) sterilized forage inoculated with parent microflora gives similar fermentation result as untreated control forage and (III) this methodology enables studying interactions between forage source and field flora on silage fermentation and aerobic stability. Hypothesis (I) was evaluated by constructing regression models of end-products on common forage chemical variables (e.g. dry matter, crude protein) and lactic acid bacterial numbers using data from 66 maize and 52 perennial crop silages. To address hypothesis (II), grass, grass-clover, white clover and maize samples were sterilized by heating, inoculated with parent microfloras and ensiled. Validation was made against untreated control silages. To test hypothesis (III), grass, red clover and maize samples were sterilized by heating and each sterile sample was inoculated with each of the three microfloras, derived from intact samples, before ensiling. (I) On average, the models captured 43% and 52% of total variation in end-product concentrations in perennial crop and maize silages, respectively. (II) Reconstituted silages contained lower amounts of lactic acid, ethanol and ammonia (i.e. 18%, 20% and 37%, respectively) but similar amounts of volatile fatty acids and 2,3-butanediol and had similar microbial profiles compared to control silages. (III) Forage source had marked effects on both end-product formation and silage aerobic stability whereas, field flora mainly affected the aerobic stability. It is concluded that the new in vitro methodology, in spite of needs for further improvement, allows hypothesis testing on relative effects of field flora and forage species on silage quality. The results also suggest that more detailed information on forage chemical composition, such as data on water activity, pectin, organic acids, etc., could provide additional information for the prediction of ensiling outcome.
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