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The various amino acids (AA) provided by the rumen-synthesized microbial protein (MCP), ruminal protein (RUP) and endogenous protein (ECP) are the raw materials for ruminant body tissues and milk protein synthesis. A small amount of absorbed AA is necessary for the body to synthesize other metabolic precursors. Therefore, AA nutrition is very important for ruminant nutrition research. With the establishment of new protein systems in various countries, the ruminant AA nutrition has gradually developed towards modularization. In particular, the establishment of the US CNCPS system in the 1990s linked protein nutrition to carbohydrate nutrition and established a dynamic model describing the use of AA in the small intestine. In the 21st century, people are increasingly inclined to apply various new technologies to regulate the metabolism of AA at the organizational level. This article will mainly introduce the hotspots of AA nutrition research on ruminants in recent years.
1 Research progress on ruminant restricted amino acids (LAA)
Restricted amino acids (LAA) and its compositional patterns are important factors in determining the utilization of nitrogenous substances in ruminants. By regulating the balance of absorbable LAA, the amount of dietary protein can be reduced, and the utilization rate can be improved, thereby saving resources and reducing environmental pollution. AA absorption efficiency, transport efficiency, absorption and discharge ratio are the basic methods for assessing the LAA sequence (NRC 2001). On this basis, the feeding experiment, the duodenum (true stomach) AA perfusion method and the multi-vasive sputum technique (Shen Xiangzhen, 2004) were used to establish the LAA system. The study agreed that Lys and Met are the first and second LAA of ruminants, and the academic community is still controversial about the rest of the AA restriction sequence. This is due to differences in rumen microbes, diet and animal species, production goals and research methods. Wang Hongrong (1998) assessed the different LAA sequences of the three protein feeds. Greenwood and Tigemeyer (2000) considered that the LAA sequence of growing cattle was Lys, Met, Thr. McCuistion (2004)
The LAA sequence of the growing cattle is considered to be Lys, Met, His. Dong Xiaoling (2003) studied the LAA of Inner Mongolia cashmere goats. The relative restrictive order of various AA according to nitrogen deposition was: Cys (72.17%), Ser (54.25%), Arg (51.76%), Met (29.07%). ), His (20.45%); LAA of Inner Mongolian cashmere goats are Met and His. However, Yu Yuguo (2004) believes that Met is not the main LAA that affects cashmere growth. There is also controversy about the impact of LAA on the performance of ruminants. Studies have shown that perfusion or feeding of rumen-protective LAA can increase lactation and improve milk composition (Harrison et al 2000; Robinson et al 2000). However, Bernard et al. (2004) suggested that supplementation of rumen-protective LAA had no effect on milk yield. NRC (2001) summarized a large number of studies showing that: 1 milk protein content is more sensitive than the milk production to the response to supplementation of Lys and Met, especially after the milk production peak. 2 The increase in milk protein content has nothing to do with milk production. 3 Casein is the most affected part of milk proteins. 4 Milk protein increase is most sensitive to the addition of Lys and Met when other AA in the metabolizable protein reaches or is close to the estimated requirement. 5 In terms of milk production, early lactation cows are more sensitive to Lys and Met than mid- and late-stage. Wang Hongrong and Dong Xiaoling (2004) described some new indicators for evaluating LAA, such as molecular biological indicators, urinary 3-methylhistidine (MMH)/inosine ratio, restricted amino acid index (LAAI), protein turnover and so on.
2 Ideal Amino Acid (IAA) model and amino acid balance theory research progress
The most important factor affecting protein utilization efficiency is the small intestine digestible AA model, but the degradation of feed by rumen microbes affects the application of the IAA model in feed preparation (Boisen et al. 2000). In recent years, with the application of computer technology in animal nutrition, the ruminant IAA model and AA balance can be evaluated through more complex mathematical models. Fistula, perfusion nutrition techniques and multi-vasive sputum techniques provide an important tool for the study of ruminant AA balance patterns. Wang Hongrong (1998) found that the improved muscle model was the digestible IAA mode (M85+C15) of the growing small intestine of sheep, namely Lys 100%, Met+Cys 39.37%, Thr 76.17%, His 40.51%, Arg 72.25%, Leu 157.54%, Ile 81.47%, Val 104.75%, Phe 81.02% and Trp 12.94%, EAA: NEAA 1:1.01. Yu Yuguo (2002)
It is believed that under the condition of AA imbalance, increasing protein level is actually a kind of compensation for AA imbalance, but this compensation is limited. Excessive compensation is a waste of protein resources, and it does not reach the ideal increase. Cashmere effect. After AA balance, the peripheral tissue, especially the skin, can be used for the utilization of methionine. The amount of Met entering the duodenum from the anterior stomach is reduced, which increases the amount of skin protein synthesis and promotes the growth of villus fibers. The study also showed that within a certain range, the animal body can regulate the AA in the blood circulation by self-stabilizing and regulating functions. Once beyond the control of the animal itself, some AA stay in the blood circulation, which will affect the AA balance. At the same time, it is also indicated that the small intestine absorbable IAA mode is a range. In this ideal mode range, the animal's self-regulation function of the body makes the AA mode of entering the organizational metabolic level tend to the ideal equilibrium mode (Lu Dexun, 2004). To this end, Yu Yuguo introduced the Amino Acid Blance Index (AABI) concept to evaluate the absorption of AA balance in the small intestine. Compared with the sheep IAA model established by Wang Hongrong, the ratio of sulfur-containing amino acids (SAA) in cashmere goats is about twice that of sheep, Leu and Ile are significantly lower than sheep, and other amino acids. The difference is not big. Since the visceral tissue consumes a large amount of Leu, when the IAA formula is calculated according to the muscle and fluff mode, the actual need of Leu is underestimated. Therefore, under the premise of the IAA model determined by the Saitama Institute, the amount of Leu added should be increased. At the same time, Ile and Ser ratio should also be increased. Su Pengcheng et al. (2004) used the same method to determine the apparent digestibility of AA in the small intestine of Inner Mongolian white cashmere goats, and assessed the balance of AA. The results showed that under the condition of corn-soybean-type diet, the small intestine could absorb AABI of 0.69. To reach the equilibrium mode of M85+C15, Met, Arg, His, Thr, Ser and Trp need to be added.
3 ruminant can use amino acid research progress
Utilizable amino acid (uAA) refers to an amino acid that reaches the duodenum of a ruminant and can be digested by ruminants. Sources of uAA that reach the duodenum include MCP and RUP. Zhao Guangyong (2005) believes that the ruminant uAA concept and its measurement technology can correctly reflect the metabolic process of nitrogen-containing compounds in the rumen, and can quickly, accurately and cost-effectively evaluate the nutritional value of commonly used feed proteins in ruminants. Although the small intestine digestible AA system and the metabolizable AA system can reflect these three requirements, the calculation is more complicated and limits the application in ruminant production. With the development of various ruminant uAA requirements, the uAA system will be widely used in ruminant diet coordination. Zhao and Lebzien (2002) used u's rumen fluid fermentation to determine uAA. The results showed that in vitro culture techniques can be used for feed uAA determination. And there was a significant correlation between uAA (X, g/kg DM) calculated in vivo and uAA (X, g/kg DM) measured in vitro (Y=0.85X-6.67, r2=0.85, P<0.001, n =33). This result again indicates that in vitro culture techniques can be used for the determination of feed uAA. Zhao Guangyong (2005) also explored the possibility of using sheep fecal buffer instead of rumen fluid as an inoculum to determine feed uAA.
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