Effect of three grass combinations on the nitrate reduction in rumen fluid of Hu sheep

A 3 × 3 Latin square design was used to investigate the effect of feeding Leymus chinensis or equal proportion of alfalfa hay (Medicago sativa) and oat grass (Avena sativa) on dynamic changes of nitrate nitrogen content and fermentation characteristics of Hu sheep. Rumen fluid was obtained at 0, 1, 2, 3, 4, 5 and 6 h after feeding to determine the concentration of nitrate and nitrite and fermentation parameters. Blood samples were collected at 2 h after feeding to determine the blood methemoglobin content. The results showed that, 1) the concentrations of nitrate and nitrite in rumen fluid increased to the maximum level at 1 and 2 h after feeding, respectively, and then decreased rapidly. 2) There was no significant difference in the pH value and percentage of nitrate and nitrite among groups (P>0.05); however, ammonia nitrogen (NH3-N) concentration in group A was significantly lower than that in the other groups (P=0.018). 3) All the groups had a low concentration of blood methemoglobin, and no significant difference was observed among them (P>0.05). In conclusion, different grass combination in this study had no effect on nitrate reduction process in the rumen of Hu sheep.