ABSTRACT:The objectives of the present study were: (1) to detect protein secondary structures using the Fourier transform infrared spectroscopy (FTIR), and (2) to investigate the relationship between protein secondary structures and their rumen degradation kinetics in dairy cattle. The study was carried out using FTIR to estimate protein molecular structure of eight different types of samples, such as soybean meal, cottonseed meal, rapeseed meal, distilled dried grains with solubles, and corn. Nutritive values of these samples were determined using the Cornell Net Carbohydrate and Protein System. The results showed that: (1) different feed protein sources had different percentages and ratios of α-helixes and β-sheets in their protein secondary structures, (2) the higher protein α-helix to β-sheet ratio resulted in lower PB3 and PC, and higher PB1 and PB2 in the feeds, and (3) the α-helix to β-sheet ratio of the rumen degradation residues was changed along with the rumen degradation.

The objective of this study was to investigate the relationship between the protein secondary structure and the protein rumen degradation kinetics and the protein fractions of mixed feedstuffs of soybean meal with distillers dried grains with solubles (DDGS) at five mixed ratios (DDGS to soybean meal: 100 : 0, 70 : 30, 50 : 50, 30 : 70, 0 : 100). The Fourier transform infrared (FTIR) as a novel and cheap approach was used to detect the protein secondary structure, and the in situ nylon bag method was used to measure degradation kinetics of protein. Protein fractions were classified based on the Cornell net carbohydrate protein system. The results showed that (1) with the increasing soybean meal rate, the ruminal degraded protein and fractions of PB1 and PB2 were changed, (2) a higher α-helix to β-sheet ratio could result in a higher ruminally degraded protein, lower PB3 and PC, and higher PB1 and PB2 fractions in the feedstuff. So, mixing processing changed the feedstuff protein molecular structure spectral feature, which could influence the rumen degradation kinetics and protein fractions. It was inferred that protein degradation rate in mixed feedstuff can be measured by FTIR. There is an increasing need for protein structure evaluation and the studies on evaluating the protein nutritive values of feedstuff have become a global research focus. Protein is one of the most important nutrients in human and animal diet. Soybean meal and distillers dried grains with solubles (DDGS, co-product of fuel ethanol production) have high protein content and are mainly used as an important