The Study On Protein Secondary Structures Of Combined Feeds Of Soybean Meal With Ddgs In Rumen Degradation Characteristics And CNCPS Protein Fractions

Studying the secondary structure of proteins leads to an understanding of the components that make up a whole protein, and such an understanding of the structure of the whole protein is often vital to understanding its digestive behaviour and nutritive value in animals. The main protein secondary structures are the α-helix and β-sheet. The percentage of these two structures in protein secondary structures infiuences protein nutritive value, quality and digestive behaviour. The objective of this study was to reveal the relationship between protein secondary structures and rumen degradation kinetics and CNCPS protein fractions of combined feeds of DDGS with soybean meal at five different combination ratios (100:0,75:25,50:50,25:75,0:100), an experiment was conducted using three Holstein cows fitted permanent rumen fistula to estimate the dynamic degradability and effective degradation rate of crude protein. The nutritive value of the feed samples was determined using the CNCPS and the protein secondary structures of the feed samples was determined by FTIR.The results showed that:(1) The rate of α-helix to β-sheet, ruminally degraded, fraction PB1, fraction PB2were increased linearly and fraction PB3, PC decreased through combination of DDGS with soybean meal at an increased rate.(2) The protein structure α-helix to β-sheet ratio in the five samples had a strongly negative correlation with effective degradation rate(r=0.9765, P=0.0043). The results indicated that the ratio of α-helix to β-sheet in the combinations could be used as a predictor for effective degradation rate.(3) There is no significant correlation between the ratio of α-helix to β-sheet in the combinations and the fraction PA. The ratio of a-helix to P-sheet had significantly positive correlation with fraction PB1(r=0.9423, P=0.0165) and fraction PB2(r=0.9727, P=0.0054), but significantly negative correlation with fraction PB3(r=-0.9588,.P=0.0111) and fraction PC (r=0.9603,P=0.0094).All in all, the changes of the protein molecular structures in the combined feeds were highly correlated with CP subfractions, in situ degradation kinetics. The results indicate that a higher α-helix to β-sheet ratio may result in a higher ruminally degraded, a lower PB3and PC, a higher PB1and PB2in the feeds. The results indicated the protein molecular structures could be used as a predictor for nutrient availability in combined feeds.