| In this experiment, four Xuhuai goats fitted with rumen cannula were selected to determine the effects of concentrate to forage rates on the nitrogen microcirculation between the rumen microbial and protozoa in vitro. The substrate for in vitro culture were designed as follows, concentrate-to-forage ratio (corn+bean : straw), A (1:9), B (3:7), C (5:5) and D (7:3) respectively, and the results are provided as below:1. As the results showed, the bacterial yield was increased correspondence with the increase of the concentrate-to-forage ratio. The bacterial yield of B was significantly lower that of A, C and D; D was higher than A and significantly higher than B, while no significant difference was detected between D and C. The N concentration of C was the highest of all, as 5.25%, and with the time increasing, the trends in each group were closer. Abundance of bacterial 15N is between 6.65~7.73 atom%, no significantly difference between B, C and A, D (p>0.05). The 15N concentration of C was the highest, as 367.13μg/30ml, and the 15N concentration of B was the lowest of all, as 257.13μg/30ml, and the peak value was appeared at 4.5 h in each group. The utilization of (NH4)2SO4 by rumen bacterial was increased correspondence with the increase of the concentrate-to-forage ratio; C is 16.79% and the highest of all. The mark rate of bacteria reached a maximum value at 1.5 h, were between 64%~73%; with the extension of time, the value showed a downward trend, thus, the best mark time is at 1.5 h.2. The grazing amount of rumen protozoa on bacterial and MCP microcirculation were affected by the concentrate-to-forage ratio, the grazing amounts of A, B, C and D were presented as follows: 18.11×105 pgN/(ml h), 21.16×105 pgN/(ml h), 20.95×105 pgN/(ml h) and 30.34×105 pgN/(ml h). It was further observed that, the grazing rates of rumen protozoa on bacteria were 25.27 pgN/(cell h), 29.69 pgN/(cell h), 23.17 pgN/(cell h) and 35.11 pgN/(cell h) for A, B, C and D respectively. Extrapolating the assimilation quantity of bacterial nitrogen by ciliates per day per capita, there were 173.88 mgN/(d capita), 203.11 mgN/(d capita), 201.14 mgN/(d capita) and 291.25 mgN/(d capita), or the bacterial protein were 1.09 gPr/(d capita), 1.27 gPr/(d capita), 1.26 gPr/(d capita) and 1.82 gPr/(d capita) respectively, with group C recording the highest circulation rate (2.79%), and group D recording the highest bacterial protein circulation amount, while group B recording the lowest circulation rate (1.94%) and the protein turnover equivalence to 69.78% of group D, which can effectively reduce the amount of bacterial protein circulation.3. The ruminal inner mricroenvironment was influenced by the concentrate-to-forage ratio. The pH was between 6.01 ~ 6.73 and decreased with the concentrate-to-forage ratio increasing; the NH3-N concentration reached the maximum value in each group after culturing 2 h, and then decreased; the NH3-N concentration of D was significantly lower than that of A, and no significant difference was detected among A, B and C. The concentration of acetic acid and the ratio of acetic acid to propionic acid decreased with the concentrate-to-forage ratio increasing, but the concentration of propionic acid and butyric acid was increased with the concentrate-to-forage ratio increasing, and molar concentration of TVFA was increased with extension of culturing time. Cell density of microbial in rumen of Xuhuai goats was significantly affected by the concentrate-to-forage ratio, the density of protozoa in group C was the highest of all (5:5), equivalent to 7.33×104cell/ml. The total of Entodiniinae,Diplodiniinae,Isotrichidae and Ophryoscolecinae was more than 90% of total protozoa in each group, and the amounts of Entodiniina and Isotrichidae were increased with the concentrate-to-forage ratio increasing, Diplodiniinae and Ophryoscolecinae, on the contrary, the increase of decrease with the concentrate-to-forage ratio.
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