Profiles of Odd- and Branched-Chain Fatty Acids and Their Correlations With Rumen Fermentation Parameters, Microbial Protein Synthesis, and Bacterial Populations Based on Pure Carbohydrate Incubation in vitro

Hangshu Xin; Nazir Ahmad Khan; Xin Liu; Xin Jiang; Fang Sun; Shuzhi Zhang; Yukun Sun; Yonggen Zhang; Xiang Li

doi:10.3389/fnut.2021.733352

Profiles of Odd- and Branched-Chain Fatty Acids and Their Correlations With Rumen Fermentation Parameters, Microbial Protein Synthesis, and Bacterial Populations Based on Pure Carbohydrate Incubation in vitro

Front Nutr. 2021 Sep 22:8:733352. doi: 10.3389/fnut.2021.733352. eCollection 2021.

Authors

Hangshu Xin¹, Nazir Ahmad Khan², Xin Liu^{1

3}, Xin Jiang¹, Fang Sun⁴, Shuzhi Zhang³, Yukun Sun¹, Yonggen Zhang¹, Xiang Li¹

Affiliations

¹ College of Animal Science and Technology, Northeast Agricultural University, Harbin, China.
² Department of Animal Nutrition, The University of Agriculture Peshawar, Peshawar, Pakistan.
³ Wellhope Feed Company Limited, Shenyang, China.
⁴ Department of Ruminant Nutrition, Institute of Animal Husbandry of Heilongjiang Academy of Agricultural Sciences, Harbin, China.

Abstract

The objectives of this study were to evaluate changes in profiles of odd- and branched-chain fatty acids (OBCFA), including pentadecanoic acid (C15:0), 13-methyltetradecanoic acid (iso-C15:0), 12-methyltetradecanoic acid (anteiso-C15:0), 14-methylpentadecanoic acid (iso-C16:0), heptadecanoic acid (C17:0), 15-methylhexadecanoic acid (iso-C17:0), and 14-methylhexadecanoic acid (anteiso-C17:0) during in vitro fermentation of pure carbohydrates mixtures in the buffer-rumen fluid. The second objective was to correlate the changes in the OBCFA profile to the corresponding changes in ruminal fermentation parameters, microbial crude protein (MCP) synthesis, and bacterial populations. Five pure carbohydrates mixtures containing different cellulose: starch (C:S) ratios, i.e., 0:100, 25:75, 50:50, 75:25, and 100:0, were incubated for 6, 12, 18, and 24 h in vitro. The results showed that there was significant interaction (P < 0.05) between C:S and incubation time for changes in all OBCFA profiles, except iso-C17:0. The highest concentration of total OBCFA (3.94 mg/g dry matter; DM) was observed in the residues after 24 h of fermentation when the C:S was 0:100, while the lowest concentration of OBCFA (1.65 mg/g DM) was produced after 6 h of incubation when the C:S was 50:50. The correlation analysis revealed that the concentration of iso-C16:0 might be a potential marker for the estimation of total volatile fatty acids (ρ = 0.78) and MCP synthesis (ρ = 0.82) in the rumen. Compared to starch degrading bacteria, cellulolytic bacteria had stronger correlations with OBCFA concentrations, and the strongest correlation was found between the population of Ruminococcus flavefaciens with C15:0 concentration (ρ = 0.70). Notably, this is the first paper reporting relationship between OBCFA with rumen fermentation products and microbial protein synthesis based on fermentation of pure carbohydrates mixtures in vitro, and thus avoid confounding interference from dietary protein and fat presence in the in vivo studies. However, more in-depth experiments are needed to substantiate the current findings.

Keywords: bacterial population; microbial protein; odd- and branched-chain fatty acids; rumen fermentation products; volatile fatty acids.