Modulation of rumen fermentation and microbial community through increasing dietary cation-anion difference in Chinese Holstein dairy cows under heat stress conditions

Abstract

Aims: The effect of increasing dietary cation-anion difference (DCAD) on rumen fermentation and ruminal microbial community in dairy cows under heat stress (HS) conditions were evaluated.

Methods and results: This study was performed as a two-period cross-over design during the summer season, with eight lactating dairy cows randomly distributed to either a control DCAD diet (CON: 33·5 mEq/100 g DM) or high DCAD diet (HDCAD: 50·8 mEq/100 g DM). Throughout the present study, the temperature and humidity index (THI; 80·2 ± 4·29) was generally elevated above the threshold (THI = 72) that is reported to cause HS in lactating dairy cows. Rumen liquid samples were collected on 15 and 21 d during each 21 d-period. The absolute concentration of ruminal total volatile fatty acid (TVFA) in HDCAD treatment was significantly (P < 0·05) higher than those in the control, whilst the ruminal pH, NH₃ -N, and VFA molar percentages were unaffected through increasing DCAD. Furthermore, the copy numbers of the cellulolytic bacteria Ruminococcus albus and Ruminococcus flavefaciens in rumen fluid significantly (P < 0·05) rose along with the increment of DCAD. Although the Alpha diversity indexes and the bacterial microbiota structure were unaffected, increasing DCAD significantly (P < 0·05) enriched the phylum Fibrobacteres and genus Fibrobacter in the microflora of rumen fluid, whilst the genera Flexilinea and Dubosiella were the most differentially abundant taxa in the control.

Conclusions: Increasing DCAD under HS conditions resulted in a greater concentration of total VFA without affecting rumen bacteria diversity or structure, although the enrichment of some cellulolytic/hemicellulolytic bacteria was observed.

Significance and impact of the study: The present study provides information on the modulation of rumen fermentation and microbial community through the increment of DCAD in Holstein dairy cows under HS conditions.

Keywords: dairy cow; dietary cation-anion difference; heat stress; rumen fermentation; rumen microflora.