| The study consisting three experiments was conducted to investigate the effect of nitrate on rumen fermentation characteristics and degradation characteristics of different roughages when Hu-sheep were adapted to dietary nitrate, and the effect of different NDF/NFC ratios on nitrate reduction.Single factor design was used in experiment1to investigate the effect of nitrate on rumen fermentation characteristics and the nitrate disappearance rate when Hu-sheep were adapted to different levels of dietary potassium nitrate (0%,0.5%and1.0%). Rumen fluid was obtained at0,0.5,1,1.5,2,4,6and8h after feeding to determine the concentration of nitrate and nitrite and fermentation parameters. Blood was collected at2h after feeding to determine the concentration of serum biochemical indices and blood methemoglobin. The results showed that:(1) the nitrate and nitrite concentration increased to maximum level at1and2h after feeding and then reduced rapidly until basicly completely disappeared at6-8h;(2) Adding0.5%and1.0%potassium nitrate had no significant effect on pH value, but significantly increased the concentration of NH3-N, protozoal and total microbial protein, the concentration of acetic acid and total volatile fatty acid, decreased the concentration of butyric acid, and rumen fermentation patterns tend to acetic acid fermentation;(3) there were no significant differences of serum biochemical between0%,0.5%and1.0%groups, and blood methemoglobin was not detected in this three treatments (<0.1%).Experiment2was carried out using nylon bag method to evaluate the effect of nitrate on the rumen degradation characteristics of four roughages (alfalfa gress, Chinese wildrye, oat grass and corn silage) when Hu-sheep were adapted to different levels of dietary potassium nitrate (0%,0.5%and1.0%). After retention in the rumen for6,12,24,48and72h, taking out the four roughages and determining the rumen degradation rates and parameters of dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF). The results showed that adding1.0%potassium nitrate can significantly increased the effective rumen degradation rate of DM, OM, CP, NDF and ADF of four roughages. In addition, nitrate also had a significant influence of the rumen degradation parameters.Experiment3was conducted to investigate the effect of different NDF/NFC ratios (A0.58, B0.71, C1.20and D0.71) on nitrate disappearance rate and rumen fermentation characteristics using4×4Latin square design. Rumen fluid was obtained at0,0.5,1,1.5,2,4,6and8h after feeding to determine the concentration of nitrate and nitrite and fermentation parameters. The results showed that the concentration of nitrite was lowest in group B (0.71). With the rise of NDF/NFC, rumen pH value was significantly increased, and the concentration of NH3-N was significantly decreased, protozoal and total microbial protein were greatest in group B, and then gradually declined. In addition, with the increase of NDF/NFC, the concentration of acetic acid and acetate/propionate ratio gradually increased, however, the concentration of propionic acid, butyric acid and total volatile fatty acids gradually reduced.In a word, the optimum NDF/NFC ratio in the diet of Hu-sheep was0.71for nitrate reduction and fermentation in the rumen under this experimental condition. |
