Effects of different levels of rapeseed cake containing high glucosinolates in steer ration on rumen fermentation, nutrient digestibility and the rumen microbial community

Abstract

This trial was conducted to study the effects of dietary rapeseed cake (RSC) containing high glucosinolates (GLS) on rumen fermentation, nutrient digestion and the rumen microbial community in steers. Eight growing steers and four rations containing RSC [GLS 226.1 μmol/g dry matter (DM)] at 0.00, 2.65, 5.35 and 8.00% DM were assigned in a replicate 4 × 4 Latin square design. The results indicated that increasing RSC levels increased the ruminal concentration of thiocyanate (SCN) (P < 0.01), decreased the ruminal concentration of ammonia nitrogen (NH3-N) and the molar proportion of isovalerate (P < 0.05), did not affect the ruminal concentration of total volatile fatty acids (VFA) (P > 0.05), decreased the crude protein (CP) digestibility (P < 0.05) and increased the ether extract (EE) digestibility (P < 0.01). Increasing RSC levels tended to decrease the abundances of ruminal Ruminobacter amylophilus (P = 0.055) and Ruminococcus albus (P = 0.086) but did not affect methanogens, protozoa, fungi and other bacteria (P > 0.05). Increasing RSC levels in the ration did not affect the ruminal bacterial diversity (P > 0.05), but it increased the operational taxonomic units (OTUs) and the bacterial richness (P < 0.05) and affected the relative abundances of some bacteria at the phylum level and genus level (P < 0.05). In conclusion, RSC decreased the ruminal concentration of NH3-N and the CP digestibility, increased the EE digestibility and partly affected the ruminal bacterial community. SCN, as the metabolite of GLS, could be a major factor affecting these indices.

Effects of dietary inclusion with rapeseed cake containing high glucosinolates on nitrogen metabolism and urine nitrous oxide emissions in steers

“…The urinary urea was from the blood synthesized in the liver by using ammonia-N (NH 3 –N) absorbed from the rumen. Our previous results showed that dietary inclusion with hot-pressed RSC decreased the ruminal concentration of NH 3 –N ( Gao et al., 2021 ). Hence, dietary inclusion with RSC should have reduced the amount of NH 3 –N absorbed from the rumen, resulting in less urea synthesis in the liver and less urinary excretion of urea in steers.…”

“…GLS are the specific compounds in brassica forages ( Clarke, 2010 ) and can be hydrolyzed into SCN, goitrin and ITC ( Oliviero et al., 2018 ). It was reported that the GLS in RSC was hydrolyzed into SCN in the rumen of steers whereas goitrin and ITC were undetectable ( Gao et al., 2021 ). The results of the present study showed that dietary inclusion with RSC containing high GLS increased both the plasma and the urinary concentrations of SCN in steers.…”

Effects of raw and fermented rapeseed cake on ruminal fermentation, methane emission, and milk production in lactating dairy cows

“…It can be however expected that dietary RC may disturb ruminal fermentation. Gao et al (2021) also reported that the inclusion of RC with high glucosinolates content in growing steers diet decreased ruminal ammonia concentration and CP digestibility without affecting total VFA concentration. Feeding RC reduced the total saturated fatty acid (SFA) profile and increased the total monounsaturated fatty acid in the rumen of dairy cows ( Goiri et al, 2021 ); however, inconsistent results were observed in milk fatty acid (FA) composition.…”

Potentials of using dietary plant secondary metabolites to mitigate nitrous oxide emissions from excreta of cattle: Impacts, mechanisms and perspectives

“…When the plants are masticated and ingested by animals, the GLS can be hydrolyzed by the myrosinase in Brassica plants or microbial enzymes in the digestive tract of animals into several bioactive products such as isothiocyanates (ITC), oxazolidine-2-thione (OZT), and thiocyanates (SCN). Previous studies showed that SCN was found in ruminal fluid as well as in the urine of beef cattle fed rapeseed meals ( Subuh et al., 1995 ; Gao et al., 2021a ), but ITC and OZT were undetectable in the fluids. The results indicated that the main metabolite of GLS in the rumen was SCN, suggesting that the hydrolyzing pathway in the rumen was different from that activated by myrosinase.…”