Effects of Cultivation Temperature and Seed Sterilization on the Dynamic Nutrient Component, Bacterial Community and Rumen Fermentation Potential of Hydroponic Barley Grass

Barley grass is an emerging forage potentially helping relieve the lack of green forage for livestock, and its nutritive value is influenced by kinds of cultivation conditions. This study was conducted to investigate the effect of cultivation temperature (25 °C vs. 30 °C) and seed sterilization (0.2% NaClO) on the dynamic changes in nutrient component, fermentation potential and bacterial community of hydroponic barley grass. The results showed that starch content (56.67%) in the barley grass gradually declined and cell wall components, crude protein, and ash concentrations increased, with 26–35% dry matter loss by 10 days of cultivation, where a higher cultivation temperature (30 °C) resulted in a higher fiber concentration (NDF 29.82% vs. 19.44%; ADF 12.57% vs. 8.02%) and a lower starch content (19.69% vs. 32.05%) while seed sterilization treatment resulted in an opposite result along with an improved dry matter recovery (73.33% vs. 70.15%). Furthermore, seed sterilization increased in vitro rumen gas production (GP48 55.97 vs. 50.50 mL/0.2 g DM) of the resulting barley grass, and its fermentation potential by 10 days of cultivation was much lower than that by 8 days. Bacterial diversity analysis revealed that seed sterilization decreased the richness and diversity of bacterial community, and the abundance of taxa Methyloversatilis, Parabacteroides, Phascolarctobacterum, Lactococcus, Pseudomonas might account for the difference in nutrient component. It is suggested that optimizing cultivation conditions like temperature and sterilization could significantly improve nutrient value and dry matter recovery of hydroponic barley grass, and the production cycle of hydroponic barley grass is no better if more than 8 days, where the bacterial community plays an indispensable role.