| Summary: | 碩士 === 國立宜蘭大學 === 動物科技學系碩士班 === 99 === Ruminants take advantage of symbiotic rumen microorganisms, which can decompose plant fiber and utilize non-protein nitrogen. However, the efficiency is low. Live Yeast (Saccharomyces cerevisiae) has been utilized as a prebiotic and probiotic for ruminants to improve fermentation of ruminal microorganisms. Nevertheless, positive effects of adding live yeast products have not been consistent, because yeast might be inactivated in the saliva or the rumen or diets change.
Experiment 1 evaluated the influence of dosages (0, 0.5, 1, 2 g/L) of live yeast, substrates (soluble carbohydrates or feeds), incubation fluids (artificial saliva, particle-free ruminal fluid or microbes-included ruminal fluid), flushing with (deoxygenation) or without CO2, and incubation times (6, 24 h) on activity of an active dry yeast product and fermentation characteristics by rumen microorganisms. No matter what kind of incubation time or fluids, the in vitro results revealed that adding yeast increased gas production and ammonia concentration when soluble carbohydrates were used as substrates. Gas and ammonia increased more with incremental yeast. With feeds as substrates, supplying yeast also elevated gas and ammonia. Moreover, it increased acetate, propionate and butyrate simultaneously, but decreased acetate to propionate ratio. However, flushing CO2 reduced gas, pH, and ammonia.
It is wasteful of over-producing of ammonia in the rumen. Experiment 2 evaluated the effect of live yeast incubation in the absent ammonia with proteins (casein protein, gelatin protein, casein peptide or casein amino acid) or carbohydrates (soluble carbohydrates or feeds) on ammonia-producing ability. Adding yeast to artificial saliva with proteins increased gas and ammonia. Gas and ammonia also elevated when adding yeast to low-ammonia rumen fluid incubation with feeds.
Experiment 3 investigated supplying fumarate (0, 10 mM) to decrease ammonia produced by using live yeast (0, 1 g/L). Fumarate is an organic acid and can improve utilization of ammonia by rumen microbes. Gas was increased by adding yeast or fumarate to in vitro incubation with rumen fluid, especially by yeast in combination with fumarate. Adding yeast increased ammonia, but fumarate significantly decreased ammonia. Acetate and propionate were elevated, but acetate to propionate ratio was dropped when both additives were used alone. On the other hand, methane to volatile fatty acid ratio was decreased by fumarate, and the mixture of yeast and fumarate still had positive effect.
Experiment 4 proceeded with an in vivo study. Supplying live yeast (0, 0.4 g/d) in combination with sodium fumarate (0, 6 g/d) to dairy goat wethers had no effect on feed intake, apparent total tract nutrient digestion and digestible nutrient intake. However, urinary N was lower and retained N was higher in wethers fed yeast-supplemented diet. There were no effects of supplements on energy and protein balance in diets, body weight, and weight gain. Although in vitro results show that ammonia was increased by yeast, but adding yeast to wethers had no effect on blood urea nitrogen. However, the supply of yeast increased plasma glucose concentration, this result is consistent with in vitro study, in which propionate was increased by yeast.
The overall results of thesis study show that adding a yeast product to incubation fluids that mimicked digestive process showed metabolic activity and could enhance ruminal microorganisms. The rise of ammonia could be explained by yeast autolysis during incubation, digestion of yeast by rumen microbes, or protein-digesting activity of yeast. Supplying live yeast in combination with sodium fumarate to in vitro incubation might decrease ammonia and had better ruminal fermentation. Retained N was increased for wethers supplemented with yeast, also reflected lower acetate to propionate ratio in in vitro experiments. It is postulated that live yeast could improve efficiency of energy use, and reduce nitrogen losses.
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