Influence of nitrate supplementation on in-vitro methane emission, milk production, ruminal fermentation, and microbial methanotrophs in dairy cows fed at two forage levels

Majid Sharifi,Mona M.M.Y Elghndour,Valiollah Palangi,Muhlis Macit,Akbar Taghizadeh,Abdelfattah Z M Salem,Soheila Abachi,Ali Hosseinkhani

doi:10.2478/aoas-2021-0087

Abstract

Abstract Modifying the chemical composition of a diet can be a good strategy for reducing methane emission in the rumen. However, this strategy can have adverse effects on the ruminal microbial flora. The aim of our study was to reduce methane without disturbing ruminal function by stimulating the growth and propagation of methanotrophs. In this study, we randomly divided twenty multiparous Holstein dairy cows into 4 groups in a 2×2 factorial design with two forage levels (40% and 60%) and two nitrate supplementation levels (3.5% and zero). We examined the effect of experimental diets on cow performance, ruminal fermentation, blood metabolites and changes of ruminal microbial flora throughout the experimental period (45-day). Additionally, in vitro methane emission was evaluated. Animals fed diet with 60% forage had greater dry matter intake (DMI) and milk fat content, but lower lactose and milk urea content compared with those fed 40% forage diet. Moreover, nitrate supplementation had no significant effect on DMI and milk yield. Furthermore, the interactions showed that nitrate reduces DMI and milk fat independently of forage levels. Our findings showed that nitrate can increase ammonia concentration, pH, nitrite, and acetate while reducing the total volatile fatty acids concentration, propionate, and butyrate in the rumen. With increasing nitrate, methane emission was considerably decreased possibly due to the stimulated growth of Fibrobacteria, Proteobacteria, type II Methanotrophs, and Methanoperedense nitroreducens, especially with high forage level. Overall, nitrate supplementation could potentially increase methane oxidizing microorganisms without adversely affecting cattle performance.

Highlights

D Khadem, 2012; Bhattarai et al, 2019)
Intake and milk production Our findings showed that increasing forage to concentrate ratio from 40% to 60% could augment dry matter intake (DMI) while reducing fat and protein corrected milk (FPCM) (P
Interaction effects indicated that the use of nitrate supplementation could reduce DMI with 60% forage level

Summary

Introduction

D Khadem, 2012; Bhattarai et al, 2019). Type I and II methanotrophs belong to g- and a-subclass of Proteobacteria, respectively (Kumar et al, 2016). Studies have shown that type II methanotrophs (e.g., Methylomirabilis oxyfera and Methanoperedens nitroreducens) can reduce nitrate to nitrite in anaerobic environments that would subsequently be converted to nitrogen (Cui et al, 2015). Since the anaerobic methane oxidation in the rumen can be expected (Kajikawa et al, 2003), the rumen microorganisms are compatible with nitrate supplementation (Zhou et al, 2012), and nitrate supplementation can be used to increase the anaerobic methanotrophic population to reduce methane generation. As there is a greater potential of nitrate toxicity with diets containing less rapid fermentable energy, we tested nitrate supplementation at different levels of forage on (1) methanotrophs and microbial population in rumen fluid, (2) methane emission parameters through gas technique, and (3) performance of dairy cows

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Conclusion