With the rapid development of animal husbandry, the shortage of feed raw materials is increasingly obvious, especially the shortage of protein feed raw materials. Therefore, for researchers, how to develop and utilize other unconventional protein resources has gradually become the focus of research. D istillers D ried Grains W ith solub Le (DDGS) has high protein, comprehensive nutritional value, large yield, cheap, and good security. As a cheap and efficient feed raw material for various livestock and poultry, it has played an increasingly important role in the development of animal husbandry in recent years.

　　At present, the research and application of DDGS in foreign countries has been relatively mature, and the amount of DDGS added in different growth stages of livestock and poultry has been clear, and has formed an open manual to guide the purchase, preservation and utilization of DDGS. Especially in the United States, with the increasing production of fuel ethanol plants, a large number of DDGS products enter the world market every year. According to the 2007 report of the Fuel Association [1], the total production of DDGS in the United States reached 85 million tons in 2006, and is expected to increase to 36 million tons in 2010. Due to the large number of DDGS manufacturers, the nutritional value and quality safety of DDGS are quite different. The author summarizes the progress of the nutritional value of DDGS and its application in pig production as follows.

　　1 Nutritional value of DDGS

　　Since DDGS can be used as an important feed raw material, the accuracy of its nutritional value plays a vital role for researchers and feed mill formulators. There are some statistical data on the conventional nutrients, amino acids, minerals and vitamins of DDGS, but some nutrients are quite different from each other. There is no comparative data of some nutrients at home or abroad, which limits the application of DDGS in feed production to a certain extent.

　　1.1 Nutritional value of DDGS conventional nutrients

　　The nutritional value of DDGS conventional nutrients is shown in Table 1, and relatively authoritative data at home and abroad are selected. It can be seen that there is not much difference in dry matter studies at home and abroad, but there is a big difference in crude protein, crude fiber, crude fat, crude ash, neutral washing fiber and acid washing fiber.

　　1.2 Nutritional value of DDGS amino acids

　　The nutritional value of DDGS amino acids is shown in Table 2. There is no detailed data on the non-essential amino acids of DDGS in the China Raw Materials Database (26th edition, 2015, the same as below), and essential amino acids are not significantly different from those of the NRC(11th Revision).

　　Table 1 Nutritional value of conventional nutrients in DDGS (%)

　　Note: NRC is the 11th revision, and China Raw Materials Database is the 26th edition in 2015

　　Table 2 Nutritional value of DDGS amino acids (%)

　　Note: NRC is the 11th revision, and China Raw Materials Database is the 26th edition in 2015

　　1.3 Nutritional value of DDGS minerals

　　The mineral nutrition value of DDGS is shown in Table 3. There is no relevant data on sulfur in DDGS in China data Base, and no relevant data on chlorine in NRC. Among them, the data of calcium and potassium in The Data base of China has a large gap with that of NRC, which is significantly lower than that of NRC. For magnesium, in contrast, the Chinese raw material database is much larger than the NRC.

　　Table 3 Nutritional value of MINERALS in DDGS

　　Note: NRC is the 11th revision, and China Raw Materials Database is the 26th edition in 2015

　　1.4 The nutritional value of DDGS

　　The vitamin nutritional value of DDGS is shown in Table 4. The NRC did not make relevant statistics on vitamins, but the Chinese raw material Database made detailed analysis and statistics on vitamins.

　　Table 4 Vitamin nutritional value of DDGS (PPM)

　　Note: NRC is the 11th revision, and China Raw Materials Database is the 26th edition in 2015

　　2. Factors influencing the nutritional value of DDGS

　　The main factors influencing the nutritional value of DDGS were the variety of raw materials, processing technology, drying temperature and time, and the mixture ratio of Distillers before solution B Les (DDS) and Distillers before consent forms, Grains (DDG).

　　2.1 Raw Material varieties

　　DDGS raw materials are corn, sorghum, wheat, etc., mainly from corn. Wang Fengdan et al. [2] showed that the quality of CORN DDGS was mainly affected by raw materials. According to the statistics from 1999 to 2011, the number of corn varieties approved by the state and provinces and cities was about 5,600 [3], so the source of raw materials and varieties, as well as the harvest season, climate, soil conditions, etc. all affected the nutritional value of DDGS to a great extent [4].

　　2.2 Processing technology

　　The processing technology also has great influence on the quality of DDGS. At present, DDGS can be produced by dry and wet methods. There is no oil immersion process in dry production, so the crude fat content of DDGS extracted is relatively high. However, there are few DDGS manufacturers in dry production at present. However, the DDGS produced by wet method have lower fat content and lower quality than DDGS produced by dry method. However, the production of alcohol by wet method has a high yield and good enterprise benefits. The DDGS quality produced by semi-dry method is between the two. Later studies found that DDGS by evaporation concentration was the best way to deal with alcohol distillate.

　　2.3 Drying temperature and time

　　The temperature and time of DDGS drying are very important, too high temperature and too long time will cause the COLOR of DDGS to deepen, smell is not right, because of the Occurrence of Maillard reaction, the COLOR of DDGS to deepen, thus affecting its quality and its use in the feed effect.

　　2.4 Mixing ratio of DDG and DDS

　　The contents of crude fat, crude protein and methionine in DDG are relatively high, while the contents of crude ash, lysine and phosphorus (P) in DDS are relatively high, and DDS contains yeast, kojic saccharification and unknown growth factors generated during fermentation [5]. During mixing, DDS can be sprayed back into DDG in part or in whole. Due to the high nutritional value of DDS, the added ratio of DDS will directly determine the nutritional composition of DDGS in corn. Meanwhile, the higher the content of DDS, the darker the color of DDGS in corn will be. Studies have shown that with the increase of the soluble DDS addition ratio, the color of corn DDGS deepens, the grain size increases, the red degree increases, and the yellow degree decreases [6,7]. It can be seen that in the process of mixed DDGS production, the ratio of the two is an important indicator affecting the nutritional composition of DDGS products.

　　3 Application of DDGS in pig production

　　DDGS is a high quality source of major nutrients such as energy, protein and available phosphorus at different growth stages of pigs. DDGS can replace some of the corn, soybean meal and dicalcium phosphate in pig diet, thus reducing feed cost. The addition of DDGS in pig diet can also reduce some intestinal diseases caused by ileocolitis.

　　Wilson et al. [8] added 0 and 20%DDGS diet to sows during pregnancy and lactation, respectively, and found that the reduced lactation feed intake occurred mainly in the first 7 days of lactation, but had no effect on feed intake in the second breeding cycle. Sows fed with a 50%DDGS diet during gestation consumed more energy, nitrogen, sulfur, and potassium than those fed without DDGS, but the digestible crude fiber rich in DDGS was beneficial for reproductive performance. The study of Barbosa et al. [9] showed that the feeding of 10-day-old weaned piglets with 10% corn DDGS or the feeding of 21-day-old weaned piglets with 30% corn DDGS had no significant effect on the daily weight gain of weaned piglets, but reduced feed intake and increased feed to meat ratio. Whitney et al. [10] showed that adding 5% corn DDGS to the diet of weaned piglets could improve the performance of piglets. When adding 25% corn DDGS, it had no significant effect on the growth performance of weaned piglets aged 19 days and weighing more than 7kg. However, high levels of DDGS reduced feed intake and daily weight gain in piglets aged 17 days and weighing less than 7 kg.

　　DDGS contains a lot of polyunsaturated fatty acids, which can improve the composition of pig carcass fatty acids. Many studies have shown that when DDGS replaced soybean meal and corn in pig diet, the meat slaughter rate and carcass quality of the experimental group were better, but the production performance was not significantly improved, while compound enzyme preparations could improve the production performance to a certain extent and improve the mineral element utilization [11-14]. Whitney et al. [10] fed growth fattening pigs with 0, 10%, 20% and 30% DDGS diet, and the results showed that there was no significant difference in growth rate and feed conversion efficiency between pigs in the group fed with 10% DDGS diet and the control group, while feeding pigs with more than 20% DDGS diet would reduce growth rate and feed conversion efficiency.

　　4 summary

　　As an important unconventional feed material, DDGS plays an extremely important role in the development of animal husbandry. But at present, China's DDGS rely on imports, domestic DDGS due to the process is not perfect DDGS and foreign production of DDGS nutritional value is relatively large gap. Therefore, how to produce high quality DDGS efficiently is the key. Due to the soil, climate and other reasons in China, the nutrient composition of corn and other raw materials is quite different from that of foreign countries. Therefore, the establishment of the nutritional value database of DDGS of different varieties of corn and the additive amount standard of different animals in different periods will also play an extremely important role in the future development.