Influence of hydrolysis rate of urea on ruminal bacterial diversity level and cellulolytic bacteria abundance in vitro

Rumen ciliates (Ciliophora, Trichostomatia) in Brazilian domestic cattle feeding on diets with crescent urea levels

Since their discovery, rumen ciliates of domestic cattle have been reported from various geographic locations. However, until now there is only one taxonomic inventory of ciliates associated with Brazilian cattle. The present study aimed to assess the community composition, relative abundance, richness, and density of rumen ciliates in Brazilian cattle, whose feeding diets were supplemented with crescent urea levels. Across all treatments analyzed, one subclass, two orders, three families, 11 genera, and 31 species of ciliates were identified. The ciliate community composition and species richness varied among the four treatments used. However, the total ciliate density was not affected by the experimental diets. We described a new entodiniid morphotype, Entodinium caudatum m. orbonuclearis, and recorded Oligoisotricha bubali for the second time in Brazil.

Ruminal Degradation of Taurine and Its Effects on Rumen Fermentation In Vitro

Taurine accounts for approximately 0.1% of an animal’s body. It cannot be used for protein synthesis but plays a wide range of important roles in the animal body. Taurine does not exist in plants, while mammals can only synthesize 30–40% of the taurine they need. Supplementing taurine to beef cattle may be necessary to improve their nutrient utilization and health status. However, no data are available regarding the metabolism of taurine in the rumen. Two in vitro trials were conducted to investigate the ruminal degradability of taurine and its effects on rumen fermentation. In Trial 1, Tilley and Terry’s in vitro rumen fermentation technique was used for incubation. As treatments, two levels of taurine, i.e., 0 and 10 mg, were added into plastic tubes containing 0.4000 g of feed mixture with a calibrated volume of 50 mL. Three adult cattle fitted with rumen cannulas were used as the donors for rumen fluid. The incubation was carried out at 39 °C for 48 h. The results showed that the taurine degradability increased with incubation time (p < 0.001) while its 2 h-degradability reached 99%. Taurine decreased the 48 h-dry matter degradability (DMD) (p = 0.008) and increased the 24 h- and 48 h-pH (p = 0.005; p = 0.018), respectively. In Trial 2, the Hohenheim gas test was used for incubation. Four levels of taurine, i.e., 0, 5, 10 and 20 mg, were added into glass syringes containing 0.2000 g feed mixture with a calibrated volume of 100 mL as treatments. The rumen fluid donors were the same as in Trial 1. The incubation was carried out at 39 °C for 48 h. The results showed that taurine increased the 48 h-pH (p < 0.001) linearly, decreased the cumulative gas production (p < 0.001) and the total volatile fatty acids (VFA) concentration (p = 0.014), and quadratically affected the ammonia–nitrogen (p < 0.001) and microbial crude protein (MCP) concentrations (p < 0.001). It was concluded that taurine was highly degradable in rumen fermentation. Taurine inhibits ruminal fermentation by decreasing DMD, VFA and gas production while improving MCP synthesis on a dose-dependent basis.

Effects of Non-Protein Nitrogen Sources on In Vitro Rumen Fermentation Characteristics and Microbial Diversity

Here, the effects of non-protein nitrogen sources on fermentation parameters and microbial diversity were explored using three fistula goats as rumen fluid donors. The experiments involved six fermenters in a replicated 3 × 3 Latin square design with three dietary non-protein sources [ammonium chloride (A), biuret (B), and glutamine (G)] as treatment factors. A dual-flow continuous culture fermentation system was used. Microbial protein content in group B was significantly lower than that in the other two groups (P &lt; 0.05). Ammonia nitrogen concentration significantly differed among the three groups (P &lt; 0.01), following the order of G &gt; A &gt; B group. The acetate-to-propionate ratio in group G was significantly lower than that in the other two groups (P &lt; 0.01). At the phylum level, the relative abundances of Cyanobacteria, Elusimicrobia, and Armatimonadetes were the highest in group G, being significantly higher than those in group B (P &lt; 0.05). At the genus level, the relative abundance of Ruminococcus_1 was significantly higher in group A than in group B (P &lt; 0.05). Overall, glutamine shifted the fermentation pathway from acetate to propionate, and the lower microbial crude protein content and relative abundances of the major fiber-degrading bacteria Ruminococcus_1 and protein-degrading bacteria Prevotellaceae_UCG-001 in group B indicate that biuret is not suitable as a dietary non-protein nitrogen source.

Urea transport and hydrolysis in the rumen: A review

Inefficient dietary nitrogen (N) conversion to microbial proteins, and the subsequent use by ruminants, is a major research focus across different fields. Excess bacterial ammonia (NH3) produced due to degradation or hydrolyses of N containing compounds, such as urea, leads to an inefficiency in a host's ability to utilize nitrogen. Urea is a non-protein N containing compound used by ruminants as an ammonia source, obtained from feed and endogenous sources. It is hydrolyzed by ureases from rumen bacteria to produce NH3 which is used for microbial protein synthesis. However, lack of information exists regarding urea hydrolysis in ruminal bacteria, and how urea gets to hydrolysis sites. Therefore, this review describes research on sites of urea hydrolysis, urea transport routes towards these sites, the role and structure of urea transporters in rumen epithelium and bacteria, the composition of ruminal ureolytic bacteria, mechanisms behind urea hydrolysis by bacterial ureases, and factors influencing urea hydrolysis. This review explores the current knowledge on the structure and physiological role of urea transport and ureolytic bacteria, for the regulation of urea hydrolysis and recycling in ruminants. Lastly, underlying mechanisms of urea transportation in rumen bacteria and their physiological importance are currently unknown, and therefore future research should be directed to this subject.

Effect of combinations of feed-grade urea and slow-release urea in a finishing beef diet on fermentation in an artificial rumen system

This study evaluated the effect of combinations of feed-grade urea and slow-release urea (SRU) on fermentation and microbial protein synthesis within two artificial rumens (Rusitec) fed a finishing concentrate diet. The experiment was a completely randomized, dose-response design with SRU substituted at levels of 0% (control), 0.5%, 1%, or 1.75% of dry matter (DM) in place of feed-grade urea, with four replicate fermenters per dosage. The diet consisted of 90% concentrate and 10% forage (DM basis). The experiment was conducted over 15 d, with 8 d of adaptation and 7 d of sampling. Dry matter and organic matter disappearances were determined after 48 h of incubation from day 9 to 12, and daily ammonia (NH₃) and volatile fatty acid (VFA) production were measured from day 9 to 12. Microbial protein synthesis was determined on days 13-15. Increasing the level of SRU quadratically affected total VFA (Q, P = 0.031) and ammonia (Q, P = 0.034), with a linear increment in acetate (L, P = 0.01) and isovalerate (L, P = 0.05) and reduction in butyrate (L, P = 0.05). Disappearance of neutral detergent fiber (NDF) and acid detergent fiber (ADF) was quadratically affected by levels of SRU, plateauing at 1% SRU. Inclusion of 1% SRU resulted in the highest amount of microbial nitrogen associated with feed particles (Q, P = 0.037). Responses in the efficiency of microbial protein synthesis fluctuated (L, P = 0.002; Q, P = 0.001) and were the highest for 1% SRU. In general, the result of this study showed that 1% SRU in combination with 0.6% urea increased NDF and ADF digestibility and total volatile fatty acid (TVFA) production.

Biochanin A Inhibits Ruminal Nitrogen-Metabolizing Bacteria and Alleviates the Decomposition of Amino Acids and Urea In Vitro

Simple Summary

Plant bioactive compounds have been chosen as alternative antibiotic to promote animal productivity. Biochanin A is a type of naturally occurring bioactive compound. It is O-methylated isoflavone and is found in red clover, alfalfa sprouts, and other legumes. The aim of this study was to determine the effect of biochanin A on rumen microbial fermentation and composition. The results show that biochanin a increases microbial gas production, but has no effect on volatile fatty acid (VFA) production. Microbial urease activity was inhibited by Biochanin A with the IC50 of 320 nM. Biochanin A also inhibited the degradation rate of Val, Lys, Met, Leu and total amino acids, respectively. The inhibition of urease activity and amino acid decomposition by biochanin A resulted in a reduction in ammonia. The 16S rRNA gene sequencing showed that biochanin A reduced the abundance of proteolytic bacteria Prevotella and Streptococcus. Therefore, biochanin A reduced the production of ammonia by inhibiting proteolytic bacteria and its decomposition of urea and amino acids activity.

Abstract

Biochanin A is a naturally occurring flavonoid compound that is found in plant species such as red clover (Trifolium pretense) and alfalfa (Medicago sativa). Flavonoids have been reported to regulate ruminal fermentation, and the objective of this study was to evaluate the effects of biochanin A on ruminal microbial composition and nitrogen metabolism. The experiment was performed by in vitro batch culturing of a control (without biochanin A) and a biochanin A treatment. Following a 24-h incubation, gas production and the amounts of ammonia-nitrogen (NH₃-N), volatile fatty acid (VFA), and amino acids were measured. Microbial population using 16S rRNA gene sequence. We found that the addition of biochanin A significantly increased microbial gas production; but had no effect on VFA production. Biochanin A supplementation also resulted in reduced microbial urease activity with half the maximal inhibitory concentration of 320 nM and also inhibited the degradation rates of total amino acids, valine, lysine, methionine and leucine by 18%, 56%, 37%, 13%, and 12%, respectively. This inhibition of urease activity and amino acid decomposition resulted in a significant reduction in the NH₃-N concentration. High-throughput sequencing of the 16S rRNA sequence to monitor microbial composition showed that biochanin A significantly reduced the abundance of the proteolytic bacteria Prevotella and ureolytic bacteria Selenomonas, but increased the abundance of the lactic acid metabolizing bacteria Veillonella and Megasphaera. In conclusion, biochanin A reduced the production of ammonia by inhibiting proteolytic bacteria and their decomposition of urea and amino acids.