Bacillus subtilis field spray on alpine meadows promotes digestibility in Tibetan sheep via increasing the nutrient quality of herbage and enhancing rumen bacterial populations

Le résumé fourni par la source

Grasslands have important ecological and economic functions. However, climate change and overgrazing contribute to the deterioration of such functions, and maintaining a balance of forage-livestock is critical to mitigate this effect. In this study, we evaluated the dose-response relationship between Bacillus subtilis ( B. subtilis ) field spray on an alpine meadow and the chemical composition of forage, digestibility and rumen bacterial populations in Tibetan sheep. Specifically, four treatment blocks were divided into 4 paddocks, which were sprayed with 1 g/L, 2 g/L and 5 g/L B. subtilis suspension, and an equal volume of water as control, respectively, and the treatment dose was 200 mL/ m 2 . Thirty-two 1-year-old Tibetan sheep (wethers) with a body weight of 30 ± 0.23 kg were rotationally grazed among 4 blocks, each containing different B. subtilis concentrations, with a 7-day grazing period in each block. The crude protein content in herbage increased with the rise in B. subtilis spraying concentration ( P < 0.01), meanwhile, crude fiber contents were negatively correlated ( P < 0.01); The apparent digestibility of crude protein, neutral detergent fiber and ether extract were higher ( P < 0.05) for sheep feeding on herbage sprayed with B. subtilis than for sheep fed with control, while it was enhanced with increasing spray concentration; B. subtilis had a lower fecal nitrogen ( N ) as a proportion of N intake ( P < 0.05) and urinary N as a proportion of N intake ( P < 0.05) than that of control, which was negatively correlated with the spray concentration gradient; The fecal energy and urinary energy output were different ( P < 0.05) among diets. Methane/ dry matter intake and methane energy/gross energy were reduced ( P < 0.05) compared with sheep fed with the control, and the maximum spray volume was the lowest; Sheep offered the B. subtilis -sprayed diet had a lower ruminal pH ( P < 0.05), which reduced with the increase in spraying concentration and with the rising content of volatile fatty acids ( P < 0.05). The acetate: propionate ratio was different ( P < 0.05) among diets, with the lowest value at a spray concentration of 2 g/L; The field spray of B. subtilis increased the relative abundances of total bacteria, and the bacteria associated with fiber degradation ( P < 0.05), and reduced those of fungi, protozoans and methanogens . In conclusion, the foliar application of B. subtilis on natural grassland could improve the nutritional value of herbage, and the growth performance and apparent feed digestibility in Tibetan sheep.

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