Effects Of Chemical Treatments On Ultrastructure Of Rice Straw And Rumen Microbial Activity

This study was proposed to investigate the effects of chimecal treatments on rumen microbial activity and ultrastructure of rice straw stem to examine the probable mechanism with which chemical treatments exerted the effects on the improvement of nutritive value of RS.Rice straw (RS) was treated with urea, ammonium bicarbonate (NH4HCO3) and sodium hydroxide (NaOH), respectively. The untreated and treated RS stem samples were examined for chemical composition, in sacco digestibility, microbial protein (MP) and carboxymethylcellulose activity and evaluated for the degradation of tissues and cell wall by using a scanning electron microscope (SEM) and a transmission electron microscope (TEM).Crude protein (CP) content of RS was increased from 10.7 (control) to 17.6 and 14.3% due to treatments with urea and NH4HCO3, but not influenced by NaOH treatment. Values for NDF were reduced slightly by NaOH and urea treatments, but showed little response to NH4HCO3 treatment. Treatments with urea, NH4HCO3 and NaOH increased the in sacco digestibility of RS from 45.3% (untreated) to 52.5, 53.2 and 63.6%, respectively (PO.01). The MP determined at 12h incubation was slightly increased (P>0.05) by the three treatments. After 24h incubation, treatments with NaOH, Urea N4HCO3 increased the MP yields by 29.5 (P<0.01) , 9.1 (PO.01) and 15.4% (P<0.01) , respectively. The MP concentration in all samples dropped at 48h incubation, but the MP yields in Urea- and NH4HCO3- treated groups were still significantly higher (PO.01) than that in the control. Chemical treatments increasedthe carboxymethylcellulose activity in in vitro fermented chyme.Treatments withNaOPL Urea f P NFL^HCOs increased the carboxymethylcellulose activity by 81.8(PO.01), 24.1 (PO.05) and 20.4% (PO.05) at 12h incubation, and by 75.4(PO.01), 18.3 (P<0.01) and 21.3% (PO.01) at 24h incubation. But after 48hincubation, the carboxymethylcellulose activity in all samples was lower than that at12h, and just the carboxymethylcellulose activity in the NaOH-treated wassignificantly higher (PO.01) than that in the control.Parenchyma was distorted by the three chemical treatments, but badly distorted by NaOH treatment. Three chemical treatments had little effect on other tissues of RS stem. All three treatments quickened the degradation of parenchyma at 12 and 24h, while NaOH treatment made the parenchyma degraded to most extent at both times. Sclerenchyma cell wall in the untreated RS was slightly digested even at 72h, but NaOH-treated sclerenchyma cell wall began to be degraded at 48h and just left the middle lamella and occasional primary wall at 72h. Sclerenchyma cells treated with urea and N^HCOa still left partial secondary wall and complete middle lamella and primary wall at 72h. All three treatments made the phloem absent at 48h, but had little effect on the digestion of epidermis and xylem of vascular tissue. These results indicated that NaOH treatment had the best effects on the modification of structure of rice straw stems and the digestion of tissues and cell wall, and that the positive effects of M-LiHCOs treatment basically paralleled those of urea treatment.In summary, the three chemical treatments all increased the MP yield, carboxymethylcellulose activity, the degradation rates of parenchyma, sclerenchyma and phloem and the extents of degradation of sclerenchyma (primarily secondary wall) to improve the digestibility and the nutritive value of RS.