Effect Of Different Sources Of Starch On Rumen Fermentation, Digestion And Metabolism Of Nutrients In Beef Cattle

This study was conducted to investigate the effect of different sources of starch on rumen fermentation, digestion and metabolism of nutrients in beef cattle. First, the effect of different sources of starch on in vitro fermentation characteristics of beef cattle was investigated, and then studied the rumen degradation of three kinds of starch by using nylon bag method. At last, the effect of duodenal infusion of different sources of starch on digestibility, energy and nitrogen metabolism, blood parameters of beef cattle was studied.In experiment 1, the effect of different sources of starch on in vitro fermentation characteristics of beef cattle was studied. Three healthy and age-mached beef cattle (312.5kg±23.85kg) with ruminal, duodenal, and ileal cannulas were used to provide rumen fluid. The experiment included four treatments:basal diet (B), basal diet plus corn starch (BC), basal diet plus glutinous rice starch (BG) and basal diet plus resistant starch (BR). Each treatment at every fermentation time point had six replicates. Analyzed and compared the composition of different sources of starch. Recorded the amount of cumulative GP at 0, 2,4,6,8,12,24,48 and 72h. After 72h incubation, the fermentation medium was used for analyzing pH, ammonia nitrogen (NH3-N), volatile fatty acid (TVFA, Acetate, Propionate and Butyrate) and microbial protein (MCP) and the relative content of Streptococcus bovis. The results showed that the composition of three kinds of starch had large difference. The corn starch had the highest content of total starch (98.08%), and the resistant starch was lowest (70.62%). The glutinous rice starch contained almost entirely amylopectin, and the content of total starch was 90.36%. The amylose/amylopectin ratio of the resistant starch was 12.7 times of the corn starch. The resistant starch had a delay time. The cumulative GP and rumen digestibility of DM at 72h of BR group was significantly lower than BC and BG group (P<0.05). The DM digestibility of BC group was highest (74.81%). There was a significant positive correlation between the digestibility of DM and the Cumulative GP (r=0.692). The content of NH3-N in BR group was significantly higher than BC and BG group (P<0.05). But the content of propionic acid of BG group was significantly higher than the three groups (P<0.05), and the ratio of acetic acid to propionic acid was significantly lower than the other groups (P<0.05). The treatments of adding starch had the higher relative content of Streptococcus bovis than the basal diet (P>0.05), and that of BG group was the highest (2.23%).In experiment 2, the rumen degradation of corn starch (CS), glutinous rice starch (GS) and resistant starch (RS) were investegated using nylon bag method at 0,2,4,8,12,24 and 36h of fermention time points. Three healthy and age-mached beef cattle (312.5kg±23.85 kg) with ruminal, duodenal, and ileal cannulas were used. Each cattle had two nylon bags of the same source of starch at each time point. The results showed that the rumen degradation of RS after 36h fermentatipn (68.49%) was significantly lower than GS and CS (3.51% and 7.45% respectively, P<0.05). The effective degradation rate and rapid degradation proportion of CS were significantly higher than the other two sources of starch (55.87% and 24.00% respectively, P<0.05). The composition of CS and RS significantly changed with the extension of fermention time (P<0.05). After 36h rumen fermentation, the content of amylose in RS dropped 26.74%, and the ratio of amylose to amylopectin lowered 1.51 times. But the CS has small range decreases (1.94% and 0.03 times respectively).In experiment 3, using 3x3 latin square design to investigate the effect of duodenal infusion of different sources of starch on digestibility, energy and nitrogen metabolism, blood parameters of beef cattle. The infusion rate averaged 250ml/h and lasted for 10h per day, the final infusion amount of starch was 400g/d. The results showed that the apparent digestibility of starch in small intestine, total tract digestibility of starch and the apparent digestibility of CP and OM in small intestine of RS group were significantly lower than CS and GS group (P<0.05). The apparent digestibility of starch in small intestine, total tract digestibility of starch were significant correlated with the content of amylose and amylopectin. There were no significant affect of duodenal infusion of the same amount of corn starch, glutinous rice starch and resistant starch on fecal energy, urine energy, fecal nitrogen, urinary nitrogen, serum free amino acids, pH and VFA values of ileal chyme (P>0.05). Duodenal infusion of different sources of starch can increase blood sugar and insulin levels, but the GS group had the largest increase (P>0.05). There were significant affect of duodenal infusion of the same amount of corn starch, glutinous rice starch and resistant starch on the a-amylase enzyme activity of duodenal chyme (P<0.05), and each group was increased at first and then decreased with the extension of infusion time.In summary, those three different sources of starch can significantly affect ruminal fermentation, rumen degradation efficiency, the digestion and metabolism of nutrients. The composition of three kinds of starch had large difference. The glutinous rice starch has nearly all of amylopectin, the corn starch has 76.18% of amylopectin, but the content of amylopectin in resistant was only 20.19%. The total content of starch and DM digestibility of fermentive substrates can significantly affect in vitro gas production. The content of propionate acid increased with the increasing of amylopectin in rumen. However, the rumen degradation of amylose in beef cattle had a delay time.The apparent digestibility of starch in small intestine and total tract increased with the content of amylopectin in rumen bypass starch. Feeding at 1.3 times of maintenance level for beef cattle, there were no significant affect of duodenal infusion of the same amount of corn starch, glutinous rice starch and resistant starch on energy and protein metabolism. The higher content of amylopectin in diet can affect the utilization rate of energy and nitrogen, the concentration of blood glucose and insulin.