The rumen microbiota and metabolism of dairy cows are affected by the dietary rate of inclusion of Yucca schidigera extract.

Natural plant compounds can be used to supplement livestock diets, improving feed efficiency, production, and health, while also reducing environmental impact. In the present study, a Yucca schidigera (Mohave Yucca) extract was added at four rates of inclusion (ROI) of 0, 5, 15, or 30 g/day to a ryegrass and maize silage-based diet and fed to dairy cows in a 4 × 4 Latin square experimental design. Each period was 28 days in duration, with sampling undertaken during the final week of each period. Solid phase digesta (SPD) and liquid phase digesta (LPD) samples were collected via a rumen cannula and analyzed for volatile fatty acids (VFAs), ammonia N, and microbiome using 16S rRNA gene sequencing. Total fecal and urine collection was undertaken over a 3-day period. Rumen microbial diversity was not affected by ROI (LPD: P = 0.180; SPD: P = 0.059). However, discriminant analysis found a decrease in Methanobrevibacter millerae (linear discriminant analysis, LDA = 2.15) and an increase in an unclassified species of Proteobacteria (LDA = 2.10) associated with ROI. Univariate analysis also revealed differential abundance of operational taxonomic units classified as Prevotellaceae and Fibrobacteraceae by ROI (P < 0.05). Maximum rumen ammonia N concentration decreased linearly from 228 to 109 mg/L with ROI (P = 0.044). Rumen VFA concentration was unaffected with the exception of propionate, which showed a linear increase with ROI (P = 0.010). The diurnal rumen pH range (maximum-minimum) also decreased with ROI (P = 0.004). Dry matter intake and milk yield were not affected (P > 0.05) by ROI; however, there was a linear increase in milk fat content from 38.9 to 42.0 g/kg with ROI (P < 0.05).IMPORTANCEDomestic livestock such as dairy cows are inefficient utilizers of dietary nitrogen. This increases feed costs and reduces animal production efficiency. Excreted nitrogenous compounds are also an environmental hazard, such as when they enter water courses as nitrate or are lost to the atmosphere as ammonia or nitrous oxide. Dietary protein is degraded in the rumen via the activity of the microbial population, mainly into ammonia, which may then be utilized by the microbial population to synthesize microbial protein or absorbed into the blood and potentially excreted. Manipulation of the diet or altering the microbial population may increase the utilization of dietary protein, increasing animal performance, decreasing feed costs, and reducing the environmental impact of milk production. This study examines the effect of Yucca schidigera extract on the rumen microbiome and nitrogen utilization in dairy cows.