Influence of harvest date of primary growth on microbial flora of grass herbages and haylage, and on fermentation and aerobic stability of haylage conserved in laboratory silos

The influence of harvest date of the primary growth of grass herbages on the microbial flora of herbage pre-conservation and haylage post-conservation was studied along with fermentation variables and aerobic stability of haylage. The primary growths of two grass swards, one intensely (Int) and one extensively (Ext) managed, were cut at three different harvest dates (May, June, August) and ensiled in laboratory silos for 120 d. Later harvest dates resulted in increased counts of yeast, mould and enterobacteria in the pre-conserved herbage (P < 0·001). Counts of lactic acid bacteria (LAB) (P < 0·001) and number of mould species (P < 0·001) were highest in the pre-conserved herbage harvested in August. Later harvest dates resulted in higher yeast (P < 0·001) and LAB (P < 0·001) counts in the haylage while counts of enterobacteria decreased (P < 0·001). Clostridial spore counts were unaffected by harvest date both in herbage and haylage. The haylage harvested in August had the lowest pH and the lowest concentration of ethanol but the concentration of lactic acid was in general low. Aerobic stability was longer (P < 0·01) for haylage from herbage harvested in August compared with haylage from herbage harvested in May and June. Sward type had less influence than harvest date on microbial variables in herbage and haylage and on fermentation variables of haylage, and did not influence the aerobic stability of haylage.