Abstract
Legumes are particularly susceptible to clostridial fermentation when ensiled because of their high buffering capacity and water-soluble carbohydrate contents. The aim of the study was to investigate if a sodium nitrite treatment (900 g t-1 herbage in fresh matter [FM]) impairs butyric acid fermentation of red clover-timothy-meadow fescue silage compared with formic acid-treated (4 l t-1 FM) and untreated silage. The sward was harvested after wilting at low dry matter (DM) (LDM, 194 g kg-1) and high DM (HDM, 314 g kg-1) concentrations and half of the herbage batches were inoculated with Clostridium tyrobutyricum spores before additive treatments. No butyric acid fermentation was observed in HDM silages probably because of the relatively high DM and nitrate contents of the herbage mixture. In LDM silage butyric acid was detected only in formic acid-treated silage, and the number of clostridia copies was higher in formic acid-treated than in sodium nitrite treated silage. Sodium nitrite treatment was superior to FA treatment in suppressing clostridial fermentation in the LDM silages.
Highlights
Clostridia can be found in silage primarily because of soil and slurry contamination during harvesting
Since lactic acid bacteria have a better osmotolerance than clostridia, higher external osmolality has a positive effect on improving silage quality (Hoedtke 2007)
Since the water-soluble carbohydrate (WSC) content was slightly higher and buffering capacity (BC) lower in high DM (HDM) than low DM (LDM) herbage the calculated fermentability coefficient (FC) was higher for HDM (42) than LDM (28) herbage
Summary
Clostridia can be found in silage primarily because of soil and slurry contamination during harvesting They can be either saccharolytic or proteolytic, and some consume lactic acid, which causes an undesirable rise in silage pH (Muck 2010). Since lactic acid bacteria have a better osmotolerance than clostridia, higher external osmolality has a positive effect on improving silage quality (Hoedtke 2007). Formic acid (pKa 3.77) has a stronger acidity than, e.g. acetic acid (pKa = 4.8), but the concentration of the undissociated molecules is lower compared to other aliphatic carboxylic acids at same pH levels (Lück and Jager 1995) This may explain at least partly the differences in the effects of formic acid in inhibiting clostridia and butyric acid fermentation
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