The Molecular Structure Of Double-Low Rapeseed Meal And Soybean Meal In Relation To Nutrient Profiles And Production Performance In Dairy Cows

The nutrient availability and feeding performance to dairy cows might be different among Chinese double-low rapeseed meal(Co PR),canola meal(Co PC)and soybean meal(Co PS).These biological differences might due to the chemical functional groups existed in feed structures.The objective of this study was to:(1)Comparison among two double-low rapeseed meal and soybean meal in: feed molecular structure features,chemical composition,metabolic characteristics and feeding performance when adding in ruminant diets,which will provide a scientific proof for rational making feed formula.(2)Establish the correlation between feed molecular inner structure makeup and traditional nutrient values and production performance,which will provide a novel research method for feed analyses and evaluation.Experiment 1: Comparison of traditional nutrient profiles among double low rapeseed meal and soybean mealThe chemical compositions of Chinese double-low rapeseed meal,canola meal and soybean meal were determined using traditional feed analyses methods.Protein and carbohydrate fractions were partitioned by CNCPS system.Truly digestible nutrient and energy value were estimated based on NRC-2001 model.The results showed that the total carbohydrate content was highest in Co PC and lowest in Co PS(P< 0.05).The neutral detergent fiber(NDF),acid detergent fiber(ADF),acid detergent lignin(ADL),cellulose,hemicellulose were higher in Co PR and Co PC than Co PS(P< 0.05).The average crude protein(CP)content of Co PS was 52.6 % DM,which was significantly higher than Co PR(44.1 % DM)and Co PC(38.4 % DM)(P< 0.01).According to CNCPS system,the soluble fiber CB2 fraction was highest in Co PS and lowest in Co PR(P< 0.05).Compared to Co PS,the total undegradable CHO faction was higher in Co PR and Co PC(P< 0.05).The unavailable protein fraction was lowest in Co PS(P< 0.05).Co PC and Co PS had higher total digestible NFC(td NFC)content than Co PR(P< 0.05).However,the total digestible CP(td CPc)content was significant higher in Co PS than Co PR,and lowest in Co PC(P< 0.05).Compared to Co PS,Co PR and Co PC had significantly higher total digestible NDF(td NDF)and total digestible nutrient at maintenance level(TDN1x)content(P< 0.05).In energy value,compared to Co PR and Co PC,the digestible energy at maintenance level(DE1x),net energy for maintenance(NEm),net energy for growth(NEg),digestible energy(DE3x),metabolizable energy(ME3x)and net energy for lactation(NELP)were significantly higher in Co PS(P< 0.05).There is no significant difference between Co PR and Co PC in predicted energy content(P> 0.05).Experiment 2: Comparision of metabolic characteristics among double low rapeseed meal and soybean mealThe rumen degradation kinetics of DM and CP in this study weredetermined using in situ nylon bag technique.The intestinal CP digestibility of rumen undegraded protein wasmeasured using the three-step in vitro method.The results showed that compared to Co PS,Co PR and Co PC had higher rumen undegraded DM and lower rumen degraded DM content(P< 0.05).Co PR and Co PC had lower potentially degradable protein fraction D and higher degradable protein fraction U in comparison with Co PS(P< 0.05).Compared to Co PC and Co PS,Co PR had higher rumen undegradable feed protein(P< 0.05)and lower effectively degradable feed protein(P< 0.05).The higher content of rumen bypass protein in Co PS and Co PC could provide more protein for intestinal absorption.The intestinal digestibility of rumen undegraded protein was highest in Co PS and lowest in Co PR(P< 0.05).The intestinal digestible protein content was significantly higher in Co PS than Co PR and Co PC(P< 0.05).The total digestible protein content was highest in Co PS(498 g/kg DM)and lowest in Co PC(335 g/kg DM)(P< 0.05).Experiment 3: Evaluating feed nutrient values of double-low rapeseed meal and soybean meal based on NRC-2001 mode and DVE/OEB modelThe nutrient value of three protein source feed was compared using NRC-2001 model and DVE/OEB model,respectively.The results showed that in NRC-2001 model,the truly absorbed microbial protein(AMCPNRC)and truly absorbed rumen undegraded protein(ARUP)in the small intestine were significantly higher than Co PR and Co PC(P< 0.05).The content of metabolizable protein synthesized in the small intestine was important for milk yield.Co PS had higher metabolizable protein(MP)than Co PR and Co PC(P< 0.05).There is no significant difference between Co PR and Co PC(P > 0.05).In DVE/OEB model,the truly absorbed rumen synthesized microbial protein(DVME),truly absorbed rumen undegraded protein(DVBE)and truly abosorbed protein(DVE)in the small intestine were both higher in Co PS compared to Co PR and Co PC(P< 0.05).There is no significant difference between Co PR and Co PC(P > 0.05).Experiment 4: Effect of feeding different protein source diets on dairy production performance,digestion characteristics and metabolizable protein synthesisThe experiment design was a 3×3 Latin Square Design.Six first lactation Australia Holstein cows were randomly assigned to three dietary treatments: Co PR,Co PC and Co PS as the major protein source feed,respectively.All dietary treatments keep the same CP contents and energy level,which could meet the nutrient demand of dairy cows.The results showed that compared to cows fed rapeseed meal(TMRCo PR)and soybean meal(TMRCo PS)as the major protein sources diets,cows fed canola meal based diet had the highest milk yield(36.63 vs.34.77 vs.32.09 kg/d;P< 0.05).In rumen fermentation features,cows fed TMRCo PS diet had higher total VFA content than TMRCo PC(P< 0.05),but not significantly different to TMRCo PR(P> 0.05).Additionally,the ratio of propionic acid in total VFA was significantly higher in TMRCo PR compard to TMRCo PS and TMRCo PC(P< 0.05).Cows fed TMRCo PR and TMRCo PC diets had lower DM and OM intake,but higher NDF and ADF intake compared to cows fed TMRCo PS diet(P< 0.05).The total tract apparent digestibility of CP,DM,OM,NDF and ADF were all highest in TMRCo PS diet group,lowest in TMRCo PR diet group,and medium in TMRCoPC diet group(P< 0.05).The content of microbial protein,truly absorbed microbial protein and metabolizable protein were significantly higher in group of cows fed TMRCo PS diet compared to TMRCo PR and TMRCo PC diets(P< 0.05).No significant difference was found between TMRCo PR and TMRCo PC diets(P> 0.05).Experiment 5: Comparison of molecular structure features among three feed sources and dietsbased onthese feed as the major protein sourcesThe protein and carbohydrate spectural features of three feed sources and diets based on them as the major protein sources were determined by ATR-FT/IR technology.The spectrum features of three feed sources showed that in the protein spectral region(ca.1720-1482 cm-1),the peak area intensity of Amide I and II,Amide I,Amide II were all lower in Co PR and Co PC compared to Co PS(P< 0.05).The ratio of ?-helix to ?-sheet peak height was highest in Co PC,medium in Co PR,and lowest in Co PS(P< 0.05).The peak area intensity of the structural carbohydrate related peaks in the spectral region ca.1482-1188 cm-1 was lower in Co PR and Co PC than Co PS(P< 0.05).The spectrum analyses of three experimental diets showed that ?-helix peak height intensity and ?-sheet peak height intensity of TMRCo PR diet and TMRCo PS diet were higher than TMRCo PC diet(P< 0.05).But the ratio of ?-helix to ?-sheet peak height intensity was lower in TMRCo PS diet and TMRCo PC dietcompared to TMRCo PR diet(P< 0.05).The ratio of structural carbohydrate to total carbohydrate peak area intensity was higher in TMRCo PR diet than TMRCo PS diet and TMRCo PC diet(P< 0.05).Experiment 6: Correlation between protein and carbohydrate molecular structure features and nutrient composition,metabolic characteristics,production performance of feedsThe PROC CORR procedure of SAS 9.3 was used for correlation analyses and PROC REG procedure was used for regression analyses.The results showed that the ratio of ?-helix to ?-sheet peak height intensity in three feed was negatively correlated to rumen undegraded protein fraction U(r =-0.68,P< 0.05),the ratio also had a close relationship with microbial protein and metabolizable protein content estimated based on NRC-2001 model and DVE/OEB model(P< 0.05).Total digestible protein TDP(g/kg DM)had a close correlation with Amide I and II structure ratio and protein ?-helix/?-sheet structure ratio.As for the correlation between carbohydrate molecular structure and DM rumen degradation kinetics,structural CHO peak area(A_STCHO)(r =0.93),cellulosic compound peak area(A_CELC)(r =0.85),peak area ratio of structural CHO to total CHO(A_STCHO/A_CHO)(r =0.73)andpeak area ratio of cellulosic compound to total CHO(A_CELC/A_CHO)(r =0.77)all positively correlated with DM rumen degradable fraction D(P< 0.05),and negatively correlated with rumen undegradable fraction U(P< 0.05).The ratio of Amide I to Amide II peak height intensity in protein molecular structure of different protein source diets had a positive correlation with the total tract apparent digestibility of DM(r = 0.83,P= 0.006),OM(r = 0.79,P= 0.011),NDF(r = 0.89,P= 0.001),ADF(r = 0.91,P= 0.001),and it also tended to positively correlated to CP total tract apparent digestibility(r = 0.64,P= 0.063).The peak height intensity of ?-helix and ?-sheet in protein second structure of different protein source diets was positively correlated to the intestinal digestibility of rumen undegraded protein(P< 0.05).Additionally,the ratio of structure carbohydrate to total carbohydrate peak area intensity in carbohydrate molecular structure of different protein sources diets was positively correlated to rumen undegraded fraction(U)(r = 0.68,P = 0.044),rumen bypass fraction of dry matter(BDM)(r = 0.73,P = 0.027),but negatively correlated to S(r =-0.71,P= 0.034)and rumen effectively degradable fraction of dry matter(EDDM)(r =-0.73,P= 0.027).Therefore,it was concluded that:(1)There is no significant between rapeseed meal and canola meal in protein and carbohydrate nutrient compositions.(2)Soybean meal and canola meal could provide more intestinal absorbable rumen bypass protein.The higher rumen degradable DM content in soybean meal could provide more energy for rumen microbe growth.Additionally,Soybean meal had higer metabolizable protein,but the degraded protein balance value was higher in soybean meal and rapeseed meal,which caused more nitrogen loss in rumen degradation.(3)The group of cows fed soybean meal based diet had higher nutrient digestibility,which could provide energy for microbe growth and metabolizable protein for dairy cows resulting in higher milk protein yield.Higher milk yield was found in cows fed canola meal.Soybean meal and canola meal are two ideal protein sources feed for dairy cows.(4)Three protein source feed had unique carbohydrate and protein spectrum features.The inner molecular structure differences were highly associated with nutrient compositions and metabolic characteristics in ruminants.(5)There existed significant difference among different protein sources diets in spectral features,and it also affected the digestibility of diets and the production performance in dairy cows.