Abstract
The objective of this study was to compare the effects of Crabtree-negative ruminal yeast and Crabtree-positive yeast in ensiled rice straw (RS) on the ensilage quality, nutritive value, and microorganism composition, including the evaluation of the ensiled RS using the in vitro gas production technique. The experiment was conducted in a 4 × 3 factorial arrangement in a randomized complete design. Factor A was yeast species with no inoculant, Crabtree-negative yeasts (Pichia kudriavzevii KKU20 and Candida tropicalis KKU20), and Crabtree-positive yeast (Saccharomyces cerevisae), whereas factor B was ensilage times (7, 14, and 21 days). The rate of growth was revealed to be lower in Crabtree-positive yeasts than the other Crabtree-negative yeast strains (p < 0.01). RS ensiled with S. cerevisiae showed decreased dry matter (DM) content by 9.0% when compared to the sample without a yeast inoculant. In addition, organic matter (OM) content was greater (p < 0.01) for P. kudriavzevii KKU20 than C. tropicalis KKU20 and without an inoculant. Neutral detergent fiber (NDF) content was significantly decreased (p < 0.01) by yeast inoculants by about 2.75% when compared to the control group. Lactic acid bacteria (LAB) and aerobic bacteria were low (p < 0.05) when yeasts were added. However, no interaction was found between yeast and ensilage times on the quality of ensiled RS (p > 0.05). The P. kudriavzevii KKU20 addition was associated with the highest value (p < 0.01) of gas produced—an insoluble fraction (b), potential extent of gas production (a + b), and cumulative gas production at 96 h—when compared with S. cerevisiae or the control group. The highest in vitro dry matter digestibility and in vitro neutral detergent fiber digestibility was observed in RS ensiled with P. kudriavzevii KKU20 for 14 days (p < 0.01, p < 0.05). The maximum total volatile fatty acids (VFAs) at 4 and 8 h of incubation and the mean value were observed in RS ensiled with P. kudriavzevii KKU20 (p < 0.01). RS ensiled with all yeast strains showed an increased propionate concentration at 8 h (p < 0.01). In conclusion, ensiling RS with isolated Crabtree-negative ruminal yeasts could benefit feed digestion and in vitro gas production more than Crabtree-positive yeast does. P. kudriavzevii KKU20, an isolated Crabtree-negative ruminal yeast used to treat RS, had the highest potential for increasing cumulative gas production and enhancing in vitro digestibility.
Highlights
Going back several years, yeast inoculants have been confirmed to improve the efficiency of feed utilization and the performance of ruminants [1]
The viable cell count in a medium solution started from 6.0 Log10 cell/mL, and the growth of P. kudriavzevii KKU20, C. tropicalis KKU20, and S. cerevisiae was 10.13, 9.73, and 9.26 Log10 cell/mL at 72 h of incubation, respectively
The rate of growth was revealed to be lower in S. cerevisiae (Crabtree-positive yeast) than in the other strain (Crabtree-negative yeast)
Summary
Yeast inoculants have been confirmed to improve the efficiency of feed utilization and the performance of ruminants [1]. The nutritional value of feedstuffs and byproducts can be improved through fermentation with yeast [2]. Rice straw (RS) is an abundant byproduct, but its nutrient levels are low, especially levels of crude protein (CP) [3]. To improve RS nutrition, yeast was chosen as an alternative solution for providing high-quality protein, vitamins, stimulatory factors, and positive functions to improve the rumen fermentation process. An earlier work by Foiklang et al [4] demonstrated that Saccharomyces cerevisiae (S. cerevisiae)-fermented RS showed enhanced gas production at 96 h and that true digestibility at 48 h increased 220 g/kg and. S. cerevisiae has become the model organism used for improving animal performance [5,6]
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