Effects Of Rare Earth Elements Lanthanum, Cerium, Praseodymium On In Vitro Rumen Fermentation, Methane Production And Microbial Flora

The objectives of the thesis were to study the effects of rare earth elements (REE) lanthanum (La), cerium (Ce), praseodymium (Pr) on in vitro rumen total gas production, methane (CH4) production, volatile fatty acids (VFA) and microbial populations.Experiment1. The objectives of the trial were to study the effects of REE La on total gas production, CH4, VFA production and microbial flora using feed mixtures with different levels of neutral detergent fibre (NDF) as substrates. Five levels of LaCl3, i.e.0,0.4,0.6,0.8and1.0mmol/kg dry matter (DM), and four levels of dietary NDF, i.e.20.0%,31.0%,41.9%and52.7%, were allocated in a two-factor5x4randomized design. The results showed that supplementing LaCl3increased the total gas (P<0.001) production, CO2and tended to increase the total VFA production (P=0.072), decreased the CH4production (P=0.001) and the ratios of acetate/propionate (P=0.019) and CH4/total VFA (P<0.001). Supplementing LaCl3decreased the ammonia N concentration and increased the uCP of feed mixture (P<0.05). Interactions between LaCl3and the NDF were significant in total gas production (P=0.030) and tended to be significant in CH4production (P=0.071). Supplementing LaCl3at the level of0.8mmol/g DM decreased the relative abundance of methanogens and protozoa (P<0.0001), increased F. succinogenes (P=0.0003) and decreased R. flavefaciens(P<0.0001) whereas did not affect R. albus, B. fibrisolvens and anaerobic fungi (P>0.05). It was concluded that LaCl3decreased the CH4production without negatively affecting feed digestion through manipulating rumen microbial flora when feed mixtures with different levels of NDF were used as substrates.Experiment2. The objectives of the trial were to study the effects of REE Ce on in vitro total gas production, CH4and VFA production and microbial flora using feed mixtures with different levels of NDF as substrates. Five levels of LaCl3, i.e.0,0.4,0.6,0.8and1.0mmol/kg DM, and four levels of dietary NDF, i.e.20.0%,31.0%,41.9%and52.7%, were allocated in a two-factor5x4randomized design. The results showed that supplementing LaCl3decreased the CH4production (P=0.049) and tended to increase the CO2production (P=0.055) whereas did not affect total gas production. No effects were observed on the total VFA production and individual VFA proportions. Supplementing CeCl3decreased the ammonia N concentration (P<0.001) whereas did not affect the uCP of feed mixture. Interactions between CeCl3and the NDF were significant in ammonia N concentration (P<0.001) and tended to be significant in total gas production (P=0.086) and CO2production (P=0.096). Supplementing CeCl3at the level of0.8mmol/g DM decreased the relative abundance of methanogens and protozoa (P<0.0001), increased F. succinogenes (P=0.0003) and decreased R. flavefaciens (P＜0.0001) and B. fibrisolvens (P<0.0001) whereas did not affect R. albus and anaerobic fungi (P>0.05). It was concluded that CeCl3decreased the CH4production without negatively affecting feed digestion through manipulating rumen microbial flora.Experiment3. The objectives of the trial were to study the effects of REE Pr on in vitro total gas production, CH4and VFA production and microbial flora using feed mixtures with different levels of NDF as substrates. Five levels of LaCl3, i.e.0,0.4,0.6,0.8and1.0mmol/kg dry matter (DM), and four levels of dietary NDF, i.e.20.0%,31.0%,41.9%and52.7%, were allocated in a two-factor5x4randomized design. The pH value of the incubation liquid of all treatments ranged from6.5to7.0. The results showed that supplementing PrCl3decreased the total gas production (P<0.001) and CH4production (P=0.048), the molar proportion of acetate (P=0.006) and the ratios of acetate/propionate (P<0.001), increased the molar proportion of propionate (P=0.027). Interactions between PrCl3and the feed NDF tended to be significant in the molar proportion of propionate (P=0.067) and the ratio of acetate/propionate (P=0.069). Supplementing PrCl3at the level of0.8mmol/g DM decreased the relative abundance of methanogens and protozoa (P<0.001), increased F. succinogenes(P<0.001) and decreased R. flavefaciens (P=0.001) and B. fibrisolvens (P<0.0001) whereas did not affect R. albus and anaerobic fungi(P>0.05). It was concluded that PrCl3decreased the CH4production while it also affect feed digestion negatively.In summary, the REE La, Ce, Pr decreased in vitro rumen methane production and changed fermentation pattern significantly. Inclusion of La, Ce, Pr is one of the effective methods to reduce energy loss to the host animal and provide theoretical basis for a decrease of greenhouse gases into the environment.