Study On Effect Of Dietary Fiber On Nitrogen Excretion In Growing Pigs

The study was conducted to study the effects of dietary fiber?DF?on nitrogen excretion in growing pigs using in vivo and in vitro methods.The study aimed to provide experimental basis for the rational application of DF in pigs'diets and for the preparation of diets to reduce nitrogen excretion.Our study included two experiments:EXP.1 Study on the fermentation characteristics and effects on nitrogen excretion related indicators of different fiber diets using an in vitro methodThe experiment was conducted to investigate and compare the fermentation characteristics and effects on nitrogen excretion related indicators of different fiber diets using an in vitro method,and the fiber with better effects on microbial fermentation and nitrogen reduction was selected for the next experiment.Wheat fiber?WF?,wheat bran fiber?WBF?and oat bran fiber?OBF?were purified from wheat,wheat bran and oat bran,respectively,using the enzyme-gravimetric method?AOAC Method 985.29?.Three fiber diets,based on maize and soybean,were formulated to contain 5%WF,WBF and OBF,respectively.The three fiber diets were undergone a stomach-small intestine digestion by simulative digestion system?SDS-II?.The digestive products?i.e.fermentation substrate?were pooled for subsequent in vitro fermentation.A total of six growing pigs,which were in good health and had similar weight,were used to collect fresh feces.In order to prepare inocula,the mixed feces and culture solution were compounded in appropriate proportions.200 mg digestive products were added into a fermentation flask filled with 30 mL of inocula,placed in an incubator at 39±0.25?.The fermentation were stopped at 4,12,24,36,48 and 72 h of incubation.Then collect samples and determine the relevant indicators.The results indicated that:in the large intestine fermentation stage,?1?there were significant differences in dry matter degradability during the in vitro fermentation?IVDMD?and total short-chain fatty acid?SCFA?concentration,pH,ammonia nitrogen?NH₃-N?concentration and microbial protein?MCP?production of fermentation broth among the three fiber groups?P<0.05?.?2?at 4 h and 12 h,OBF group had the highest IVDMD among the three groups?P<0.01?.?3?as for total SCFA concentration,at 4 h and 12 h,OBF group had a higher trend than other groups?P=0.0599;P=0.0504?;at 24 h and 36 h,OBF group was significantly higher than other groups?P<0.05?;at 72 h,OBF group and WBF group were significantly higher than WF group?P<0.01?.?4?as for pH-value of fermentation broth,at 4 h and 12 h,OBF group had the lowest values among the three groups?P<0.01?;at 24 h,36 h and 72 h,OBF group and WBF group were significantly lower than WF group?P<0.05?.?5?NH₃-N concentration of OBF group were significantly lower than other groups at 24 h and 48 h?P<0.05?and had a lower trend at 12 h?P=0.0559?.?6?as for MCP production,OBF group had the highest values among the three groups at 4 h?P<0.05?;at 12 h,24 h and at 36 h,48 h,OBF group were significantly higher than WF group and WBF group?P<0.05?,respectively.In conclusion,oat bran fiber significantly increased IVDMD,total SCFA concentration and MCP production of fermentation broth,and significantly lowered pH and NH₃-N concentration of fermentation broth.That is to say,oat bran fiber showed higher potential on microbial fermentation and nitrogen reduction,and it could be used in the next experiment.EXP.2 Effects of different levels of oat bran fiber on nitrogen excretion and related metabolites of growing pigsIn the experiment,the oat bran fiber?OBF?was used as the dietary fiber source.The industrial purified OBF were added to the basal diet at a rate of 5%,12.5%and 20%,respectively,and studied the effects of different levels of OBF on nitrogen excretion and related metabolites of growing pigs.This experiment was conducted to provide experimental basis for the rational application of DF in pigs'diets and for the preparation of diets to reduce nitrogen excretion.A total of 28 growing pigs?43.63±3.99 kg?were randomly divided into 4 groups,and each group had 7 pigs.The pigs were fed 4 diets,respectively,supplemented with 0,5%,12.5%and 20%of OBF,carried out a digestion and metabolism test.The experimental period was 14 days.During the experiment,the pigs'feed intake and body weight were recorded.At the 8th day,the total feces and urine samples were collected and collected for 7 days.At the end of the experiment,blood samples were collected from pigs'vena cava before the morning feeding.After the trial,the production performance indexes were calculated,the nutrient digestibility was measured,and the nitrogen excretion,nitrogen metabolism indexes and related metabolites were measured.The results indicated that:?1?The average daily gain and feed conversion rate of pigs were not significantly affected by the levels of OBF?P>0.05?.?2?The levels of OBF had significant effects on the apparent digestibility of DM,GE,Ash,EE and NDF?P<0.01?,but had no significant effect on the apparent digestibility of CP?P>0.05?.The apparent digestibility of DM,GE,Ash,EE and NDF decreased linearly with the increase of OBF level?P<0.01?.?3?The levels of OBF had significant effects on urinary nitrogen,total nitrogen excretion and the ratio of urinary nitrogen to fecal nitrogen?P<0.05?,and had no significant effect on fecal nitrogen?P>0.05?.With the increase of OBF level,urinary nitrogen,total nitrogen excretion and the ratio of urinary nitrogen to fecal nitrogen decreased linearly?P<0.01?,and fecal nitrogen tended to increased linearly?P=0.088?.?4?The levels of OBF had significant effects on blood urea nitrogen?BUN?and apparent biological value of nitrogen?ABV??P<0.05?,and had no significant effects on ingested nitrogen,digestible nitrogen,nitrogen retention?NR?,nitrogen apparent digestibility,blood ammonia,glutamic oxalacetic transaminase,glutamic pyruvic transaminase and L-glutamate dehydrogenase?P>0.05?.With the increase of OBF level,BUN decreased linearly?P<0.05?,ABV increased linearly?P<0.01?and NR tended to increased linearly?P=0.093?.?5?The contents of acetic acid and isovaleric acid in feces,fecal total SCFA and microbial nitrogen?MN?excretion and urinary urea nitrogen excretion were significantly affected by the levels of OBF?P<0.05?,but had no significant effects on other acids?P>0.05?.The content and excretion of acetic acid,the content of isovaleric acid and MN excretion in feces increased linearly with the increase of OBF level?P<0.05?,and urinary urea nitrogen excretion decreased linearly?P<0.05?.?6?The levels of OBF had significant effects on fecal NH₃-N excretion and urease activity,feces and urine pH?P<0.05?,and had no significant effects on urinary NH₃-N excretion and fecal water content?P>0.05?.With the increase of OBF level,fecal NH₃-N excretion and urease activity,feces and urine pH were decreased linearly?P<0.01?.In conclusion,with the increase of OBF level,dietary nutrient digestibility decreased?except CP?,but the growth performance of growing pigs were not affected;urinary nitrogen and total nitrogen excretion in growing pigs decreased significantly,and fecal NH₃-N excretion and urease activity,feces and urine pH also lowered significantly,which could effectively inhibit ammonia emissions.