Effects of dietary capsaicin and yucca schidigera extracts on rumen fermentation and rumen microflora of beef cattle

(1) Background: Capsaicin (CAP) and yucca schidigera extract (YSE) are two kinds of plant extracts, which have the potential to change rumen fermentation. Hence, this experiment was conducted to investigate whether long-term addition of CAP and YSE in beef cattle diets would affect rumen fermentation and rumen microflora. (2) Methods: In total, 45 healthy angus steers with similar body weight were selected and divided into three groups according to single factor complete randomized design, with 15 heads each. There were three treatments:(1) control, (2) 1.50g/d/steer capsaicin was supplemented to basic diet, (3) 2.40g/d/steer yucca schidigera extract was supple-mented to basic diet. (3) Results: The results showed that the concentration of ammonia nitrogen (NH3-N) in YSE group was significantly higher than that in CON group (p < 0.01), while the con-centration of NH3-N in CAP group was significantly lower than that in CON group (p < 0.01). Total volatile fatty acid (TVFA) and butyric acid molar ratio were significantly increased by YSE, while acetic acid molar ratio was significantly decreased by YSE. But TVFA was decrased by CAP compared to CON (p < 0.01). CAP and YSE significantly altered the richness and diversity of rumen microorganisms. More specifically, at the phylum level, YSE increased the relative abundance of Bacteroidota and Patescibacteria (p < 0.01), reduced the relative abundance of Firmicutes (p < 0.01) compared to CON group. At the genus level, CAP and YSE both increased the relative abundance of genera subordinate to Bacteroidetes, decreased the relative abundance of genera subordinate to Firmicutes, and YSE increased the relative abundance of Candidatus_Saccharimonas (p < 0.01) com-pared to CON group. (4) Conclusions: Capsaicin and yucca extracts can change the structure of rumen microflora, thereby improving rumen fermentation