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.
1 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 arginine research progress
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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