Effect of rare earth elements on in vitro rumen microbial fermentation and feed digestion

摘要

The objectives of this study were to investigate the effects of rare earth elements (REEs) on in vitro rumen fermentation, gas production, microbial protein synthesis and nutrient digestion using in vitro batch culture and continuous culture technique. A mixture of REE containing (g/kg) 380g of LaCIp"6HO, 521g of CeCIp"6HO, 30g of PrCIp"6HO and 69g chlorides of other light REEs. The experimental diet consisted of 885g/kg barley grain, 84g/kg barley silage and 31g/kg supplement (dry matter (DM) basis). Diet supplemented with different dosages of REE (control, no additional REE; low, 400mg/kg REE; and high, 800mg/kg REE, DM basis) were incubated for 4, 8, 14 and 24h in diluted rumen fluid. At the end of 24h of incubation, gas production and concentration of volatile fatty acid (VFA) linearly increased with increasing REE supplementation; whereas, influence of REE supplementation on VFA profile was marginal. Dry matter disappearance was not affected (P>0.10). Six dual-flow continuous culture fermenters were used in a replicated 3x3 Latin square with same treatments and same diet used in the batch culture. Mean ruminal pH (5.71) and total VFA (93.6mM) concentration were not affected by supplementation of REE. The molar proportion (mol/100mol) of acetate (39.1) and propionate (50.5) was similar among the treatments. However, the proportion (mol/100mol) of butyrate was higher with the high REE (6.6) than with low REE (5.3) or the control (5.8). Ruminal true digestibilities of organic matter (OM) (0.785, 0.811 and 0.828), acid detergent fibre (0.360, 0.431 and 0.432) and crude protein (0.496, 0.590 and 0.589) for control, low and high REE, respectively, linearly increased with increasing REE supplementation, whereas, the increase in ruminal digestibility from low to high dosage of REE was minimal. Microbial nitrogen (N) production (g/day) and microbial efficiency (gN/kg of truly fermented OM) were not affected by treatments. Improvement of ruminal digestibility of OM due to REE supplementation was attributed to the increase in digestibility of fibre and degradability of protein. The results suggest that REE supplementation improved ruminal fibrolytic and proteolytic activities.