Fermentation characteristics, aerobic stability and ruminal degradation of ensiled pea/wheat bi-crop forages treated with two microbial inoculants, formic acid or quebracho tannins

This study evaluated the effects of two commonly used microbial inoculants (Lactobacillus buchneri (LB) and Lactobacillus plantarum (LP)), formic acid (FA) and quebracho tannins (QT) on the fermentation quality, aerobic stability and in situ rumen degradation of pea/wheat bi-crop forages. Precision-chopped spring pea (Pisum sativum, var Magnus) and wheat (Triticum aestivum, var Axona) bi-crops (3:1 pea/wheat ratio) harvested at a combined dry matter (DM) content of 301 g kg-1 were used for the study. The bi-crops were conserved without (Control) or with inoculants based on lactic acid bacteria (LB (105 CFU g-1 fresh weight (FW)) or LP (106 CFU g-1 FW)), QT (16 g kg-1 FW) or FA (2.5 g kg-1 FW) in laboratory silos of 1.5 kg capacity, with each treatment being replicated six times. The pH, chemical composition, aerobic stability and in situ rumen degradation of DM, nitrogen (N) and neutral detergent fibre (NDF) after 112 days of ensilage were measured. The average pH at silo opening was 4.0, suggesting that the silages were well fermented. There were no significant effects of additive treatment on water-soluble carbohydrate, total N, soluble N, ammonia N and NDF. Lactic acid and acetic acid were the main fermentation products. High concentrations of acetic acid were found in all the treatments, indicating a heterofermentative pathway. Although FA treatment gave the most aerobically stable silage, the Control and QT-treated silages did not heat up by more than 1 °C until after 6 days of exposure to air. There were no effects of additives on DM degradation characteristics. However, the inoculants increased the rate of N and NDF degradation in the rumen, and both FA and QT reduced the effective and potential degradation of N.