Succession Of Yeast Populations With Prolonged Ensiling And During Aerobic Exposure Of TMR

Total mixed ration (TMR) is a full-nutrient diet, formulated with all necessary nutrients for livestock during specific growth stage. It has a lot of advantages over the traditional feeding system, however, deteriorating quickly when exposed to air. After ensiling, TMR silages could obtain enhanced aerobic stability than non-fermented TMR. In addition, TMR silages exhibit higher aerobic stability in comparison with single silages with high moisture content. However, the mechanisms underlying the enhanced aerobic stability remain unknown. To clarify the mechanism of enhanced aerobic stability, this study was carried out on TMR with different moisture contents and different ensiling periods. The main contents and conclusions were as follows:1. The study was undertaken to investigated the influence of moisture contents on microbial dynamics and yeast species associated with aerobic deterioration. TMR was adjusted to different moisture contents (38%,43%and48%) and used for aerobic stability test after56day of fermentation. Irrespective of moisture content, the56-d TMR silages obtained good fermentation quality, with improved aerobic stability than TMR. TMR silages with high moisture content (48%) exhibited weak aerobic stability than that with lower moisture content TMR silages with medium moisture content (43%) exhibited the best aerobic stability. In addition, the proliferation of yeast prior to aerobic deterioration were closely associated with the aerobic deterioration of TMR silages. Irrespective of moisture content, Zygosaccharomyces bailii was exclusively detected in deteriorating TMR silages. Therefore, Z. bailii probably initiate the aerobic deterioration of TMR silages.2. To have a further understanding on the association of microbial dynamics with enhanced aerobic stability, whole crop corn (WCC) and TMR formulated with WCC were used to clarify the influence of ensiling and ensiling periods on microbial dynamics that associated with aerobic deterioration. Results indicated as follows:(1) WCC and TMR silages were all preserved well and exhibited higher aerobic stability than non-fermented materials, irrespective of ensiling periods. Aerobic stability of both silages were significantly enhanced (P<0.05) with prolonged ensiling. TMR silages exhibited higher aerobic stability than WCC silages for the same ensiling periods.(2) Yeast probably initiated the aerobic deterioration of TMR silages, whereas, for WCC silages, yeast and aerobic bacteria might both function during aerobic deterioration. With prolonged ensiling, aerobic bacteria seemed to play less role in initiating aerobic deterioration of TMR silages.(3) For short-ensiled (7d and14d) TMR silages, more yeast species seemed to participate in initiating the aerobic deterioration, as indicated by the yeast species detected during deteriorating period. With prolonged ensiling, fewer yeast species seemed to be involved in aerobic deterioration and Z. bailii was the only species that was detected during deteriorating long-ensiled (28d and56d) TMR sialges. Therefore, Z bailii was most likely to initiate the aerobic deterioration of long-ensiled TMR silages. In addition, the inhibition of yeast species, particularly for Pichia kudriavzevii(Issatchenkia orientalis) probably account for enhanced aerobic stability of long-ensiled TMR silages.(4) According to the tolerance and assimilation properties of isolated yeast, acetic acid was the main inhibitory factor for yeast species. P. manshurica and Z. bailii played more role in aerobic deterioration of short-ensiled and long-ensiled TMR silages, respectively. Z. bailii is capable of assimilating acetic acid other than lactic acid. The further utilization of acetic acid by Z bailii or loss by volatilization would reduce the antifungal effect created by high acetic acid and facilitate the growth of other microorganisms. Furthermore, species of P. manshurica that was predominant in deteriorating WCC silages was not detectable in deteriorating long-ensiled TMR silages. The predominant yeast species of Z. bailii in deteriorating long-ensiled TMR silages was not observed in WCC or WCC silages. Therefore, the inclusion of WCC might not influence the role of yeast species in deterioration of TMR silages.