Effects Of Different Ratios Of Ruminally Degradable Protein To Ruminally Undegradable Protein On Ruminal Fermentation And Nutrient Digestion And Metabolism In Luxi Cattle Fed Distillers Grains-based Diets

The objective of this research was to investigate the effects of different ratio of ruminally degradable protein to ruminally undegradable protein on ruminal fermentation and nutrient digestion and metabolism in Luxi cattle fed distillers grains-based dietsExperiment 1:Three Luxi cattles fitted with ruminal, duodenal and ileal fistulae were used in a 3×3 Latin square design to determine the effects of different ratios of ruminally degradable protein (RDP) to ruminally undegradable protein (RUP) on the ruminal internal environment parameters. The RDP/RUP were 1.00:1.00 (A),1.22:1.00 (B),1.50:1.00 (C), respectively. Intakes of diets were about 1.5 times of maintenance requiment of body weight during experiment. Diets were offered twice daily at 08:00 and 20:00, respectively. Cattles had access to fresh water at libitum. The results showed that:1) ruminal pH was not affected by RDP/RUP (P>0.05), and the average pH was 6.53-6.94(A), 6.44-6.84(B) and 6.45-7.03(C). The minimum value of ruminal pH was observed at 2 to 4 h after feeding, then ascended gradually; 2) increasing dietary ratios of RDP to RUP increased ruminal total VFA concentration and propionate concentration (P<0.05), decreased acetate/propionate ratio (P<0.05), but did not affect ruminal acetate concentration and butyrate concentration (P>0.05). Dynamic variation trends of ruminal both total VFA concentration and propionate concentration were originally increased and then decreased after feeding, but ruminal acetate concentration was opposite and the variation extent of butyrate was small all along; 3) the highest ruminal urea-N concentration was observed in group C, higher than group A and B (P<0.05). Ruminal urea-N concentration of all groups peaked at 10:00, but its variation tendency was different at night. The ruminal urea-N concentration of group A and B were higher during night and lower during day, but group C was inverse; 4) RDP/RUP didn't affect ruminal NH3-N concentration (P>0.05), and there was a peak value of ruminal NH3-N concentration at 2 h after feeding and then declined gradually.5) increasing ratio of RDP/RUP increased ruminal MCP production, and ruminal MCP production of group A and B were much lower than that of group C (P<0.05). The production of all groups reached lowest at 2 h after feeding, and then was increased gradually. These results suggest that dietary ratio of RDP to RUP does not affect ruminal pH and dynamic variation tendency of both ruminal NH3-N concentration and ruminal MCP production are also not affected by dietary ratio of RDP to RUP. The average both ruminal urea-N concentration and ruminal MCP production are increased by increasing dietary RDP/RUP ratio.Experiment 2:Experimental animal, design, method, and administration were all the same to experiment 1. This experiment was conducted to investigate the influence of different ratios of RDP to RUP on ruminal microbial population in Luxi cattle. Results showed that no significant difference (P>0.05) was observed in Ciliate protozoa population at 0 h, but significant decrease (P<0.05) with increasing dietary ratios of RDP to RUP at 6 h; ruminal Genus ruminococcus population did not differ (P>0.08) across treatments at 0 h, but was increased (P<0.05) with increasing dietary RDP to RUP ratios at 6 h; before feeding, ruminal Prevotella ruminicola population of group B was significantly higher than that of group A (P<0.05), but did not differ (P>0.05) between group B and group C, and then 6 h after feeding, ruminal Prevotella ruminicola population of both group A and group C were higher (P<0.05) than group B, but no significant difference (P>0.05) between group A and group C; there was no significant difference (P>0.05) in ruminal Butyrivibrio fibrisolvens population across treatments at both 0 h and 6 h; ruminal Streptococcus bovis population of group C was extremely higher (P=0.01) than that of both group A and group B at 0 h, but ruminal Streptococcus bovis population of group A was significantly higher (P<0.05) than that of both group B and group C at 6 h. This suggested that increasing dietary ratio of RDP to RUP contribute to decreasing ruminal Ciliate protozoa population, Prevotella ruminicola population, and Streptococcus bovis population, and increasing ruminal Genus ruminococcus population, but did not differ ruminal Butyrivibrio fibrisolvens population.Experiment 3:Experimental animal, design, method, and administration were all the same to experiment 1. The objective of this experiment was to evaluate the effect of different dietary ratio of RDP to RUP on nutrient digestion, nitrogen (N) metabolism and purine derivatives excretion in Luxi cattles fed distillers grains-based diets. Results showed that 1) there were no significant differences (P>0.05) in dry matter (DM), organic matter (OM), and neutral detergent fiber (NDF) intake across treatments. Increasing dietary ratio of RDP to RUP increased (P<0.05) apparent ruminal and total tract DM, OM, and NDF digestibility, but did not affect (P>0.05) apparent small intestinal DM, OM and NDF digestibility; 2) N intake did not differ (P>0.05) across treatments. Increasing dietary ratios of RDP to RUP significantly increase (P<0.05) urinary N excretion (g/d) and urinary N excretion/total N output (%), but significantly decrease (P<0.05) fecal N output (g/d) and fecal N output/total N output (%), and significantly increase (P<0.05) total tract N digestibility. There was a significant decrease in N retention expressed as g/d and/or% of digestion, and an increasing trend (P<0.10) expressed as% of intake.; 3) microbial nitrogen (MN) production and blood urea nitrogen concentration significantly were increased (P< 0.05) with increasing dietary ratio of RDP to RUP. MN synthesis efficiency (g MN/kg apparent digestible OM) of group B was significantly higher (P<0.05) than that of group A, but no significant difference (P>0.05) between group B and group C; 4) increasing dietary ratio of RDP to RUP resulted in a linearly increase in blood serum uric acid concentration (P=0.01) and increasing trends (P<0.10) in blood serum xanthine oxidase activity, allatoin concentration, and total purine derivatives (PD) concentration; 5)significant increases (P< 0.05) were observed in urinary allatoin, uric acid and total PD excretion with increasing dietary ratio of RDP to RUP. The relative proportion of urinary allantoin was decreased (P< 0.05) and urinary uric acid was increased (P<0.05) as urinary total PD excretion was increased with increasing ratios of RDP to RUP. these suggested that increasing dietary ratio of RDP to RDP can contribute to increasing ruminal and total tract nutrient digestibility, but did not affect small intestinal nutrient digestibility. Decrease in N retention and increase in urinary N excretion to the environment were observed with increasing dietary ratio of RDP to RUP. Therefore, the optimum dietary ratio of RDP to RUP was considered 1.00:1.00 regarding N retention in Luxi cattle fed distillers grains-based diets.Under fed iso-caloric and iso-nitrogenous diets, dietary ratio of RDP ro RUP had effects on ruminal fermentation, microbial population, nutrient digestion and N metabolism in Luxi cattle fed distillers grains-based diets. Increasing dietary ratio of RDP to RUP may contribute to increase ruminal total VFA, propionate acid, MCP concentration, decrease ruminal Ciliate protozoa population, increase Genus ruminococcus population, MN synthesis, OM and NDF digestibility. Decreasing dietary ratio of RDP to RUP may contribute to increase ruminal Prevotella ruminicola population and Streptococcus bovis population, decrease urinary N excretion, increase N retention. Therefore, the optimum dietary ratio of RDP to RUP was considered 1.00:1.00 regarding N retention in Luxi cattles fed distillers grains-based diets.