Histidine is an amino acid containing an imidazole heterocycle. Like other amino acids, it is an integral part of the protein structure and is involved in animal body protein synthesis. At the same time, it also widely participates in various physiological and biochemical processes of the body in various forms, including the formation of a variety of physiological and biochemical active ingredients, elimination of intracellular oxides, and involvement in immune regulation. Therefore, histidine plays an important role in animal nutrition.
Histidine is an essential amino acid of animal Since his body can synthesize histidine from a common intermediate metabolite, histidine has long been considered as a non-essential amino acid. However, as the study progressed, it was found that the amount of histidine synthesized in young animals and infants could not meet the normal growth of the organism (Kopple and Swendseid, 1975). Even if it is an adult animal, if histidine is not added from food, In vivo synthesized histidine also can not meet the needs.
Histidine-deficient animals exhibit a corresponding lack of symptoms, and many scholars have studied histidine deficiency. The symptoms of histidine deficiency mainly include: 1 negative nitrogen balance; 2 decreased serum albumin; 3 plasma and muscle free histidine decreased; 4 hemoglobin decreased; 5 hematocrit decreased; 6 muscle carotene peptide content decreased; 7 The content of copper and zinc in whole blood is reduced; 8 Serum iron is elevated. After supplementation with histidine, the above symptoms are alleviated or eliminated. Therefore, in order to ensure the normal function of the body, quantitative histidine must be taken from the diet. Therefore, although the body can synthesize histidine itself, histidine is still an essential amino acid. Histidine has been listed as an essential amino acid for pigs and chickens.
Histidine nutrient requirement The histidine content in the cereal feed is 0.2%-0.4%, while the protein feed is generally 0.6%-1.5%. The highest content is blood meal, and the lowest is feather meal. Fuller et al. (1979) found that histidine in barley is likely to be the third limiting amino acid after lysine and threonine.
Brudevold and Southern (1994) reported that histidine is the same as isoleucine, tryptophan and valine in the low protein (12%) “sorghum-bean meal†diet of 10kg-20kg piglets. Third limiting amino acid. Therefore, attention should be paid to the lack of histidine in diets with low protein levels. The content of histidine in common feed ingredients and the relevant digestibility values ​​are shown in Table 1.
Easter and Baker (1977) used a nitrogen balance test to determine the histidine requirement for sows in the first gestation. When histidine is less than 0.12%, nitrogen retention is inhibited, but the difference is not significant, so it is recommended that the pregnant sow's histidine requirement is 0.12%; Burns et al. (1982) found that the young hound achieves optimal growth performance. Histidine was required for the deposition of nitrogen and was 0.21%; Quam et al. (1987) investigated the histidine requirement for young cats for growth and hematopoiesis, with an average daily gain of 0.2% for histidine 0.2%. Sedimentation and feed intake reached the highest values, and histidine concentration was 0.3%. Hemoglobin and hematocrit were the highest. The level of histidine in the diet was linearly correlated with the logarithm of plasma free histidine (r2). =0.99), so they suggested that the cat's histidine requirement was 0.30%; Wilson et al. (1980) thought that the cat's histidine requirement was 0.37%, which accounted for 1.54% of the dietary protein; for the pig group Research on nutritional requirements for amino acids is rare. In the 1950s, several studies were conducted. However, due to the small number of animal heads used in the trials and the low level of growth, the test results could not accurately estimate ammonia levels. Acid nutritional requirements. In 1968, Mitchell et al used a homozygous diet with N retention as an indicator to estimate a histidine requirement of 0.2% for a 10kg piglet. However, there were only 2 pigs per treatment and the feed restriction was adopted. Kim et al. (1983) used the histidine levels in the diet to indirectly estimate the histidine requirement for 14C-labeled phenylalanine oxidation. When the histidine is greater than 0.4%, the phenylalanine oxidation rate is the lowest, and when the histidine is less than 0.4%, the phenylalanine oxidation rate increases with the decrease of the histidine level, indicating that when the histidine is greater than 0.4%, the phenylpropylamine The rate at which amino acids are used for protein synthesis is not limited. Therefore, the recommended amount of histidine nutrition is 0.4%. With the conception and practical application of the ideal protein concept, it has been recognized that when studying the nutritional requirements of each amino acid, particularly essential amino acids, the content of other amino acids must be considered. Table 2 shows the histidine content in pigs and the recommended ratio of histidine to lysine in several typical pig ideal protein models. The histidine content in growing pigs is higher than recommended in ideal protein models. The data of Chung and Baker (1992c) originated from the results of Izquierdo et al. (1988). From the results of Izquierdo et al. (1988), the requirement of lysine and histidine was not higher than 100:30. Therefore, the appropriate proportion of histidine in the ideal protein model is worth further exploration. In addition, homozygous diets are mostly used in studies to establish an ideal protein model, and therefore the required amount is available. When actually catering to diets, digestible or available histidine values ​​should be used as much as possible.
Conclusion Although histidine is an essential amino acid, it is generally less likely to be absent than other essential amino acids. Extra synthesis of histidine is only required in special diets with lower protein content. At present, people do not pay enough attention to the research on the nutrition requirement of histidine (NRC, 1998), so the data in this area are very few. Considering the various physiological functions of histidine, the restrictive order of histidine in actual animal diets, especially low protein diets, remains to be further studied in future studies.
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