Nitrate improves ammonia incorporation into rumen microbial protein in lactating dairy cows fed a low-protein diet

Rong Wang, Min Wang*, Emilio M. Ungerfeld, Xiu Min Zhang, Dong Lei Long, Hong Xiang Mao, Jin Ping Deng, André Bannink, Zhi Liang Tan

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

11 Citations (Scopus)

Abstract

Generation of ammonia from nitrate reduction is slower compared with urea hydrolysis and may be more efficiently incorporated into ruminal microbial protein. We hypothesized that nitrate supplementation could increase ammonia incorporation into microbial protein in the rumen compared with urea supplementation of a low-protein diet fed to lactating dairy cows. Eight multiparous Chinese Holstein dairy cows were used in a crossover design to investigate the effect of nitrate or an isonitrogenous urea inclusion in the basal low-protein diet on rumen fermentation, milk yield, and ruminal microbial community in dairy cows fed a low-protein diet in comparison with an isonitrogenous urea control. Eight lactating cows were blocked in 4 pairs according to days in milk, parity, and milk yield and allocated to urea (7.0 g urea/kg of dry matter of basal diet) or nitrate (14.6 g of NO3 /kg of dry matter of basal diet, supplemented as sodium nitrate) treatments, which were formulated on 75% of metabolizable protein requirements. Nitrate supplementation decreased ammonia concentration in the rumen liquids (−33.1%) and plasma (−30.6%) as well as methane emissions (−15.0%) and increased dissolved hydrogen concentration (102%), microbial N (22.8%), propionate molar percentage, milk yield, and 16S rRNA gene copies of Selenomonas ruminantium. Ruminal dissolved hydrogen was positively correlated with the molar proportion of propionate (r = 0.57), and negatively correlated with acetate-to-propionate ratio (r = −0.57) and estimated net metabolic hydrogen production relative to total VFA produced (r = −0.58). Nitrate reduction to ammonia redirected metabolic hydrogen away from methanogenesis, enhanced ammonia incorporation into rumen microbial protein, and shifted fermentation from acetate to propionate, along with increasing S. ruminantium 16S rRNA gene copies, likely leading to the increased milk yield.

Original languageEnglish
Pages (from-to)9789-9799
JournalJournal of Dairy Science
Volume101
Issue number11
Early online date30 Aug 2018
DOIs
Publication statusPublished - Nov 2018

Keywords

  • dissolved hydrogen
  • microbial protein
  • nitrate
  • rumen fermentation

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    Wang, R., Wang, M., Ungerfeld, E. M., Zhang, X. M., Long, D. L., Mao, H. X., ... Tan, Z. L. (2018). Nitrate improves ammonia incorporation into rumen microbial protein in lactating dairy cows fed a low-protein diet. Journal of Dairy Science, 101(11), 9789-9799. https://doi.org/10.3168/jds.2018-14904