The reproductive efficiency of sows determines the quality and economic benefits of a farm, and the reproductive efficiency of sows is affected by many factors. High temperature heat stress is considered to be an important environmental factor that causes changes in sow productivity. Arginine exerts multiple nutritional and physiological effects in the body, studies the effect of arginine on the performance of sows under heat stress conditions, and clarifies its mechanism of action, which is of great significance for pig production.
1The effect of high temperature heat stress on sows
Stress is the sum of the body's non-specific response to various internal or external abnormal stimuli, and is the response of animals to internal or external stimuli or challenges. Heat stress refers to the response of an animal in an extremely high temperature environment to the upper limit temperature of the comfort zone of the thermal environment. Pigs are warm-blooded animals, and there is an isothermal zone. Within this range, pigs maintain normal body temperature by physical regulation. Once this range is exceeded, normal body temperature is maintained by heat production and heat dissipation. Thermal stress occurs when the ambient temperature exceeds the upper limit of the comfort zone in the isothermal zone. The fat under the pig skin is thick, the sweat glands are not developed, the heat energy in the body is slow, and it is not good to regulate the body temperature by evaporating heat from the skin, so the pig is not heat-resistant.
Summer high temperature is one of the main factors affecting the reproductive function of sows. In most parts of China, the heat caused by hot summer heat in the pig industry is very serious. It has been reported that the feed intake and milk yield of sows are reduced in high temperature environments, ultimately reducing the growth rate of piglets (Quiniou et al., 1999; Quiniou et al., 2000; Renaudeau et al., 2001).
The fertility of sows is regulated by many physiological processes, and the damage of the body caused by high temperature stress is also multifaceted. Under high temperature conditions, electrolyte metabolism is disordered, and blood sugar, protein, and enzyme activity are changed. Sows also change their endocrine function under heat stress. Maloyan et al (2002) pointed out that the stimulation of heat stress in pigs activates the hypothalamic-pituitary-adrenal axis, which leads to increased secretion of corticotropin-releasing hormone in the hypothalamus, which is released into the pituitary portal system, thereby promoting pituitary secretion of the adrenal gland. Corticosteroids (ACTH). The increase of ACTH secretion inhibits the secretion of gonadotropin FSH and LH in the anterior pituitary. The inevitable result of the decrease of LH secretion is the inhibition of follicular development and inhibition of ovulation, which also reduces the secretion of estrogen and inhibits luteal production and progesterone secretion. In the production, it causes various reproductive disorders in sows. In addition, elevated levels of ACTH also indirectly affect ovarian function, can induce ovarian cysts, decreased sexual function, and hindered reproduction. In addition, high temperature reduces the secretion of thyroxine in the sow's plasma to inhibit metabolic function in the body, reduce heat production, and maintain the body's heat and heat balance at high temperatures (Prunier et al., 1997).
Heat stress caused by high temperature also causes damage to tissue cells. Heat stress induces the production of large amounts of free radicals in the body, producing a variety of deleterious effects (Mitchell et al., 1983), leading to cellular metabolism and biological dysfunction, such as fatty acid oxidation and protein synthesis dysfunction (Jiang et al, 2008). Studies have shown that free radicals in the body can alter the function of the cell membrane, which in turn triggers a variety of biological diseases (Lu Dayong et al., 1999). In the normal life process, free radicals are necessary for life support. The animal itself has two systems of oxidation and anti-oxidation. Under normal physiological conditions, the two are in dynamic equilibrium. When livestock and poultry are under high temperature and heat stress, the physiological metabolism of cells is disordered, resulting in the decline of antioxidant system function and the generation of a large number of free radicals (Mitchell et al., 1983). At this time, the excess amount of free radicals exceeds that of antioxidant system. Ability, the body is in oxidative stress (Sies, 1997). Therefore, high temperature environment can cause oxidative stress damage in animals.
2 Research progress of arginine
2.1 Biochemical and physiological properties of arginine
Arginine is a basic amino acid that exerts biological functions in the form of physiologically active L-arginine in vivo. It is not only an essential amino acid for animal protein synthesis, but also a synthetic precursor for various biologically active substances, such as polyamines and NO. Arginine is the only substrate for the synthesis of NO, and the arginine-NO pathway plays an important role in animals. Under normal circumstances, the demand for arginine in adult animals can be met by endogenous synthesis, but under stress conditions, endogenous arginine can not meet the needs of the body. Therefore, arginine is considered to be a conditional essential amino acid (Kong Xiangfeng et al., 2009).
2.2 Endogenous synthesis of arginine
Endogenous synthesis of arginine has two pathways. One is arginine, which can be glutamine, pyrrolic acid-5-carboxylic acid synthase, proline oxidase, ornithine transaminase, ornithine transacetylate. It is synthesized by glutamine (Gln) and proline (Pro) under the catalysis of enzyme, arginyl succinate synthetase and arginine succinate decomposing enzyme. In addition, ornithine and plasma citrulline in the mitochondria are also precursors for the synthesis of arginine, and citrulline further synthesizes arginine in the cell fluid. For mammals, the synthesis of endogenous arginine involves the small intestine-kidney metabolic axis, citrulline is synthesized by glutamate and glutamine in the intestine, and about 83% of the citrulline released by the small intestine is transported to the kidney. The cytosol arginyl succinate synthetase and arginyl succinate lyase are synthesized as arginine (Wu et al., 2007).
2.3 arginine metabolic pathway
Studies have shown that L-arginine metabolism has three pathways in the body, one is arginine catalyzed by nitric oxide synthase (NOS) to produce NO, and produces citrulline; the second is in arginine-degrading enzyme Under the action, arginine produces ornithine and urea, which can also be decomposed into ornithine and creatinine by glycine transylase; third is polyamine produced by ornithine, polyamine is putrescine, spermidine And the general term for spermine, plays an important role in regulating cell growth and development. Arginine degradation is mainly done in the small intestine.
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2.4 The role of arginine and its metabolites on the body
2.4.1 The role of arginine NO pathway in the cardiovascular system
The study found that the L-arginine-NO pathway is very important. NO is a very strong diastolic vascular substance (Radomski et al., 1991) and plays an important role in maintaining constant vascular tone and regulating blood pressure stability. L-arginine is a precursor of NO production. L-arginine supplementation promotes NO production and promotes vasodilation and angiogenesis. On the contrary, L-arginine deficiency leads to a decrease in NO production, which in turn affects angiogenesis. And development. Studies have shown that NO plays a role in the cardiovascular system by activating cytosyl cyclase (GC) in cells and increasing the concentration of cyclic guanosine monophosphate (cGMP) to accomplish various physiological functions such as vasodilation (XIAO Libo et al. 2009).
2.4.2 NO pathway of arginine and its regulation of immunity
There are many ways in which arginine affects immune function, but it is mainly achieved through the arginine-NO pathway and the regulation of endocrine hormones. It plays an important role in regulating body immunity and intestinal mucosal function protection. Arginine also promotes the production of immunoglobulins and effectively enhances humoral immunity. Arginine is the only substrate for the synthesis of NO, which synthesizes NO under the catalysis of NOS. NO is an important immunoregulatory factor, and its regulation of the immune system mainly includes (Li Xia et al., 1996): 1 regulates T lymphocyte proliferation and antibody response, inhibits mast cell reactivity; 2 regulates T cells and giant The phagocyte secretes cytokines; 3 promotes the activity of natural killer cells, activates monocytes in peripheral blood; 4 mediates apoptosis of macrophages. In addition, NO can relax gastrointestinal smooth muscle, regulate gastrointestinal mucosal blood flow, thereby maintaining mucosal integrity, maintaining gastrointestinal mucosal barrier function; also inhibiting leukocyte migration to the injury site, while reducing intestinal mucosal permeability, thereby reducing the intestinal tract Mucosal damage. Studies have shown that dietary supplementation with arginine enhances the immunity of pregnant sows and newborn piglets, thereby reducing morbidity and mortality in piglets (Jobgen et al., 2006).
2.4.3 The role of arginine in endocrine
Arginine can stimulate the body to secrete growth hormone and insulin. Arginine is metabolized to produce ornithine, which in turn produces glutamate, both of which promote the body's release of growth hormone. In addition, NO synthesized by arginine under NOS catalysis can also promote the release of growth hormone. Arginine can also stimulate the release of insulin from humans and other mammals including pigs, cattle and sheep. Growth hormone and insulin play an important role in the metabolism of sugars and proteins in the body tissues.
2.4.4 The role of arginine in anti-oxidative stress
L-arginine is a free radical scavenger of the body (Jiang et al., 2000). NO is a catalyzed reaction between L-arginine and molecular oxygen. It is a novel cell information molecule with dilated blood vessels and platelets. Aggregation, inhibition of cell proliferation, inhibition of lipid peroxidation and formation of glycosylation end products (Xiong et al., 1994). In general, NO exerts beneficial physiological effects in small doses. In large doses, it often causes disease or worsens the condition (Yue Xu et al., 2002), and an appropriate amount of NO can scavenge oxygen free radicals (Beligni et al. , 2002; Wink et al., 2001). In recent years, a large number of studies have been conducted on the application of L-arginine in the prevention and treatment of free radical damage in rats. Supplementation of L-arginine in rats can increase the activity of antioxidant enzymes, reduce the content of malondialdehyde (MDA), and reduce oxidation. Stress damage to rats (Huang et al, 2009; Lin et al, 2008), improve the body's antioxidant capacity. Supplementation of L-arginine can promote the production of NO, and increase the activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in tissues, and reduce the content of MDA, indicating that it is refined. Oxygen supplementation of NO can significantly reduce oxidative stress in rats. The anti-oxidative stress of L-arginine in vivo is mainly achieved by the L-arginine-NO pathway (Le Kangfu et al., 2005; Trisha, 2006; Assumpcao et al., 2008).
3 arginine in the nutrition of sows
3.1 Effects of arginine, NO and polyamine on placenta and fetal growth and development
Sow pregnancy 30-40d is a critical period of uterine development, therefore, its development directly affects the growth and development of the fetus during pregnancy. Studies have shown that the development of uterus during pregnancy is not only related to the nutritional status of sows, but also to the synthesis and utilization of NO and polyamines in the body. NO is a major vasodilator produced by endothelial cells and has a strong vasodilating effect, which plays a very important role in improving the supply of fetal blood, nutrients and oxygen to the placenta (Bird et al., 2003). Polyamines regulate the synthesis of DNA and proteins, ultimately regulating cell growth and development (Flynn et al., 2002). Many studies have shown that NO and polyamines are important regulators of increased blood vessel numbers, embryonic development, and fetal placental growth (Reynolds et al., 2001). Arginine is a common substrate for NOS and ornithine decarboxylase and produces NO and polyamine, respectively (Wu et al., 1998). Therefore, arginine may be a limiting amino acid that affects fetal growth and development. Studies have found that sows have a particularly high level of arginine and ornithine in the allantoic fluid, and the activity and concentration of NO and polyamine synthase are also maximal (Wu et al., 2005). Poor malnutrition or overnutrition in sows affects the amount of arginine in sows and also reduces the synthesis of placental NO and polyamines (Wu et al., 1998).
3.2 Endogenous arginine in suckling piglets can not meet the needs of their optimal growth
Insufficient arginine not only affects the growth and development of the fetus, but also affects the growth of newborn piglets. Arginine is an essential amino acid in suckling piglets, and insufficient supply of lactated arginine is an important factor limiting the maximum growth of newborn piglets (Wu et al., 2000). The experimental data of artificial feeding piglets showed that the growth potential of piglets after birth was at least 400g/d (from birth to 21 days old), while that of suckling piglets was only 230g/d. Compared with newborn piglets, 7-day-old suckling piglets reduced the synthesis of arginine and citrulline in the small intestine by 70%-73%, and further decreased at 14-21d. Therefore, the endogenous arginine synthesis in piglets is gradually reduced during lactation. Flynn et al (2000) showed that the concentration of NO in plasma of 7-12d in suckling piglets also gradually decreased, and the blood ammonia concentration gradually increased. Feeding 7-21d suckling piglets with 0.2% and 0.4% arginine diets showed that arginine diet increased plasma arginine concentration, decreased blood ammonia concentration, and piglet body weight gain. Increase by 28% and 66% respectively (Kim et al., 2004).
3.3 Effects of arginine on reproductive performance of sows
Domestic and foreign literature reports that the effect of arginine on the nutritional physiology of sows is mainly focused on improving the reproductive performance of sows. Laspiur et al. (2001) studied the effects of dietary arginine supplementation on the performance of lactating sows during lactation. The results showed that the addition of 1.34% arginine to the diet could improve the feed utilization rate of the sow, but had no significant effect on the performance of the suckling piglets. Ramaekers et al. (2006) added 25 g/d arginine to the diet at 14-28 days of primiparous and sows, increasing the average litter size (1.25 litters per litter and 1.18 heads, respectively). The number of litters and litters (1.08 heads/well and 0.93 heads/well, respectively). In addition, Mateo et al. (2007) studied the effect of adding arginine on the reproductive performance of primiparous sows in gestational sows 30-114d gestation. The results showed that the addition of arginine in the diet increased plasma arginine. The levels of acid, ornithine and proline also increase the number of litters and litter weight in the primiparous sows. Mateo et al. (2008) reported that the addition of arginine to lactating sows improved the growth performance of piglets. The above results indicate that supplementation with arginine in sow diets can increase litter size in sows and also improve piglet growth performance.
In conclusion, studying the protective effect of nutrients on body damage under high temperature and heat stress environment is the development direction of current special nutrition research. The role of single amino acids has attracted more and more scholars at home and abroad. After familiarizing with and understanding the effects of high temperature heat stress on the physiological function and production performance of sows and the metabolic pathway of arginine in the body, further grasp the anti-oxidative stress of arginine and play a guiding role in production practice. . Although the sow can synthesize arginine endogenously, it is insufficient under stress conditions. Appropriately increasing the supply of arginine in the sow diet at this stage is an important measure to improve the reproductive performance of the sow.
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