Ideal amino acid model for suckling pigs

There are many researches on the protein requirement and amino acid requirement of suckling pigs, and there are also many disputes. This article summarizes the results of some studies and reviews them in the hope that they will be able to initiate the study and fully think about the nutrition of suckling pigs.

First, on the ideal pig protein model

The study of the model was based on the literature. There are many corn-bean meal diets. Different researchers have different ideal amino acid models.

It is generally believed that there is only one optimal amino acid balance for the whole growth period of a pig, and the proportion of amino acids in the body or muscle of growing pigs of different body weight or age is quite stable. The general reasons are as follows: 1) The proportion of total needs due to maintenance needs is very high. Small (3-6%), the growth of pigs on the amino acid balance requirements mainly determined by the growth; 2) different gender or weight of growing pigs, the body amino acid ratio is quite constant, the difference in amino acid requirements is only the absolute amount of difference, The ratio between amino acids is always the same; 3) Proteins with high biological activity and amino acid ratios are similar to muscles. 4) Differences in amino acid requirements are greatly reduced when expressed in relative proportions based on lysine. It is also one of the theoretical basis for the establishment of the "ideal protein" system since the late 1970s. Hess (1999) also reported that the amino acid composition of a body protein generally does not depend on body weight, genotype, and variety. Important "ideal proteins" systems are the UK model of Rowett Institute and Fuller (1989, 1990), the British ARC (1981) model, the American Ilinois University Chung and Baker (1992) model, and the American NRC (1998) model. The ARC (1981) model is based on the amino acid balance in amino acid tissue in lean tissue, and Fuller et al. based on maximal nitrogen deposition in pigs, and Baker et al. based on the results obtained from homozygous diets supplemented with crystalline amino acids. The NRC (1998) is based on data derived from literature research.

The evaluation index of the ideal protein system for pigs also develops in a variety of aspects such as nitrogen deposition, protein utilization efficiency, and immune function. Different evaluation indicators have different amino acid requirements. For example, amino acids required for the growing pig to achieve optimal immune status or maximum nitrogen deposition are more than those required to obtain the maximum weight gain rate (Xiao et al., 1999; Cline et al., 2000).

However, the growth and development of pigs is a gradual improvement process. Compared with 20 kg or more growth and finishing pigs, the growth and development of pigs is not only the ratio of the need for maintaining N to occupy total N, but also the need to maintain N. The various amino acid balance modes may also be different. The former needs more N to maintain the metabolism of the muscle itself, while the latter has more N to maintain the need to consume non-muscle metabolic function. This is reflected in the fact that the required amino acid requirement pattern for pigs below 20 kg is closer to that of the carcass or the milk of pigs. For example, intestinal proline may be synthesized from dietary arginine, ornithine, glutamine, aspartate, and arterial-derived glutamine, and the pig's small intestine is the major site of synthesis (Murthy et al., 1996; Matthews, 1993). However, the synthesis of proline from arginine in suckling piglets' intestine cells is less, and the arginine synthesis induced by arginase in the intestine is significantly increased after weaning piglets. This explains the biochemical mechanism of why valine is very good. It is an essential amino acid for suckling piglets rather than an essential amino acid for growing pigs after weaning (Chung et al., 1993). Therefore, applying the ideal protein model of growing pigs to suckling pigs is open to question.

Second, the characteristics of digestive tract development of suckling pigs

Internal organs (ie, liver, intestine, etc.) grow faster in the suckling piglet stage, while other organs (eg, reproductive organs) develop faster in the late growth stage. Since the amino acid composition of each tissue is different, the requirement for dietary amino acids also varies with the growth and development of the tissue.

The traditional view is that all the amino acids digested and absorbed by the digestive tract can enter the portal vein and be used by extra-intestinal tissues without being metabolized by the intestinal mucosa. However, recent studies have shown that not all amino acids that are absorbed in feeds enter the portal vein but rather are metabolized in the gut and other organs (Dai et al., 2004). Ebner et al. (1994) showed that the effect of protein malnutrition on neonatal piglets on overall growth was mainly to reduce the growth of carcasses without affecting the growth of the gastrointestinal tract, demonstrating that intestinal development is a priority at this time.

Intravenous perfusion of neonatal piglets maintained the overall growth rate, but after 7 days of perfusion the intestinal weight was reduced by 52%, while the amount of leucine absorbed in the portal vein was increased by 30% (Burrin et al., 1994, 1999), and the increased absorption of amino acids was mainly observed. It is to reduce the use of arterial-derived amino acids in the visceral tissue, suggesting that a 50% reduction in the weight of the intestine not only does not affect the digestion and absorption of dietary nutrients, but also increases their efficiency for growth, which compensates for the growth of animals from metabolic perspectives. Provide a reasonable explanation.

Intestinal and venous infusion measurements of the metabolism of 13C-lysine and 13C-threonine fed high-protein (25%) and low-protein (10%) diets found that low protein diets were reduced Piglets grew 50% but the relative weight of the intestine did not change; net utilization of lysine in visceral tissue increased to 85% of the dietary intake, which was significantly higher than the 47% of diets fed high-protein ( Van Goudoever et al., 2000). Furthermore, it was found that the lysine used in the visceral tissue of the group fed with the high-protein diet was all from the arterial blood, and the intestine of the group fed with the low-protein diet was equally using the lysine derived from the intestine and artery. This shows that the requirement for lysine in the intestine is relatively high in the case of long-term protein intake, and preferential use of lysine from the dietary sources.

Stoll (1999) measured the rate of protein synthesis in some tissues and tissues using isotope-labeled amino acids. He found that liver and pancreas had the fastest rate of synthesis, followed by the small intestine, slower in the large intestine and kidney, and the slowest in muscle and heart. Bregendahl et al. (2003) measured the FSR of plasma and visceral organs of weaned piglets at different physiological effects with a single intraperitoneal injection of the stable isotope phenylalanine at a single intraperitoneal dose. It was also found that the rate of protein synthesis was the fastest in the pancreas and lower in the large intestine. Small intestine. See Table 1.

Therefore, the nutrition of suckling pigs should be more focused on the nutritional needs of the development of the digestive tract, rather than the muscle development needs of growing pigs.

Third, the digestive enzyme system development of suckling pigs

Different enzyme activities determine what types of diets are needed; the developmental focus of this physiological stage determines the differences in their nutritional needs.

The secretion and type of digestive enzymes in piglets depend on the piglet's age, weight, and diet. Although suckling suckling pigs can effectively secrete digestive enzymes that digest colostrum and dairy products, enzymes that secrete and digest more complex plants and other animal products lack enzymes. As piglets grow, their ability to secrete enzymes that digest complex proteins and starch in plants and other animal products continues to increase.

There is a process in the development of digestive tract and its enzyme system in piglets. A large number of data indicate that the activity of pepsin in piglets is low during the first 2 weeks after birth, and then rapidly increases with the increase of age. The pancreas and small intestine brush border enzymes Development must become complete when the piglets reach 6-8 weeks of age. The intestinal mucosal digestion and absorption function of piglets earlier than 3 weeks old and the immune function of the intestinal tract against exogenous stimuli (such as feed antigens) have not yet fully developed. The results of comprehensive AKP and ANAE found that the earlier the weaning, the smaller the intestinal mucosal injury of piglets The larger the digestive capacity of the small intestine is, the worse the digestive ability of the small intestine will ultimately affect the growth of piglets (Gu Xianhong, 2000).

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