采食是动物维持生存所必需的活动，充足的采食量更是发挥其生产潜力的必要保证。影响采食量的因素有很多，包括环境因素、动物因素、饲料因素等。在生产实践中，饲养动物不可避免的会遭遇饲料更换、冷热刺激、发情期狂躁好斗等因素影响，产生应激反应，从而降低采食影响生产效益。近年来对动物采食量调控的研究越受到重视，主要是添加外源添加剂通过神经调节、体液调节等方式来提高采食量。据报道称，γ-氨基丁酸(γ-amino butyric acid，GABA) 具有促进动物采食量、抗应激、镇静等生理功能。
Foraging is a vital activity for animal survival and production. Adequate food intake is necessary to ensure the survival of animals and to better realize their productive potential. There are many factors affecting feed intake, including environmental factors, animal factors, feed factors and so on. In production practice, it is inevitable that feeding animals will suffer from feed change, cold and hot stimulation, manic and aggressive factors in heat, and produce stress response, so as to reduce the influence of food intake on production efficiency. In recent years, more and more attention has been paid to the research on the regulation of feed intake in animals. γ-amino butyric acid (GABA) has been reported to promote physiological functions such as food intake, anti-stress and sedation.
GABA is a widely available inhibitory neurotransmitter in mammals. In recent years, the academic community has done a lot of research on feeding GABA in animal diets to fight stress and improve food intake.
Overview of GABA and its physiological functions
GABA, also known as aminotyrosine, is the product of glutamic acid (Glu) under the action of glutamic acid decarboxylase (GAD) by the -decarboxylation reaction. GABA is an important inhibitory amino acid neurotransmitter in the central nervous system, and it has different modes of action in different parts. The mode of GABA action in the brain is dominated by post-synaptic inhibition, while that in the medulla is dominated by presynaptic inhibition.
The physiological functions of GABA are mainly reflected in its regulation of normal physiological functions of the body, mainly including lowering blood pressure, calming nerves, delaying cell aging and anti-stress. In addition, GABA has an obvious regulatory effect on feed intake in animals.
Mechanism of improving food intake
目前，对GABA调控采食量的作用机制已有较多报道，下面仅就GABA 调控采食量的3 种最被认可的途径作初步介绍。
The mechanism of GABA regulating feed intake has been widely reported. Now we choose the three most recognized approaches for your information.
Inhibits satiety centers
饱觉中枢位于下丘脑腹内侧核( VMH)，机体通过感应血液和下丘脑中葡萄糖浓度，将信息传递到VMH，再由饱觉神经调节采食。GABA 在VMH中是促进采食的信号分子。当葡萄糖缺乏时，会引起VMH中GABA 浓度升高，从而导致采食增加。
The satiety center is located in the ventromedial hypothalamus nucleus (VMH). The body sends the message to VMH by sensing glucose levels in the blood and hypothalamus, then the satiety nerve regulates feed intake. GABA is a signaling molecule in VMH that promotes feed intake. When glucose is deficient, the concentration of GABA in VMH increases. An increase in GABA concentration leads to an increase in feed intake.
Feed intake is regulated by acting on the taste response
There are three subtypes of taste receptor cells (TRCs). The taste reflex functions through inter-cellular communication among the three subtypes of taste. TRCs are directly administered by the central nervous system. Studies have shown that GABA in the cells of animal taste buds is involved in taste regulation, and microinjection of GABA into the medial medulla oblongata of animals can increase feed intake.
Synergies with NPY to promote feed intake
NPY is called neuropeptide tyrosine. In the central nervous system, NPY has various biological functions such as promoting animal feed intake, affecting hormone secretion, sexual behavior, and temperature regulation. NPY neurons go through a series of signal transductions, which eventually inhibit the sympathetic and excitatory parasympathetic nerves, trigger a strong series of ingestion responses. GABA is a promoter of the dietary effect of NPY. GABA promotes the secretion of NPY and increases the concentration of NPY in the blood, which in turn increases the feed intake.
The mechanism of GABA to alleviate heat stress
Heat stress refers to the non-specific response of the body to high temperature. Due to global warming, heat stress is becoming one of the most important factors to harm livestock production. Heat stress will accelerate the catabolism of fat, glycogen and protein in the body, resulting in the decrease of feed intake and feed remuneration.
Heat stress mainly affects the performance of livestock and poultry production in two ways. One is to activate the HPA axis and the inhibitory nervous system. The other is to reduce the plasma concentration of two thyroxine [triiodothylamine (T3), tetraiothylamine (T4)]and insulin,but increase the concentration of corticosterone (CS) to affect the process of nutrient anabolism.
GABA is the main nerve antagonist in the nervous system, which has the effects of heat stress and sedation. GABA mediates the passive action of most central and peripheral nerves. In the case of heat stress, dietary GABA can significantly improve the body weight, feed intake, daily weight gain, carcass weight, and blood T3 and insulin concentration of feed animals, as well as significantly reduce the concentration of CS in the animal blood to alleviate the effect of heat stress. In addition, dietary addition of GABA can improve the activity of serum antioxidant indexes SOD and GSH-PX, reduce the activity of MDA which reflects the damage degree of cell membrane, significantly reduce the concentration of three hormones-COR, CORT and ACTH, and obviously reduce the body's heat stress response.小结 Summary
GABA can increase feed intake in animals by inhibiting the stimulation of satiety nerve, regulating the taste response, and promoting the secretion of NPY (an accelerant of feeding effect). In addition, GABA can also reduce stress response by inhibiting central nervous system response and hormone secretion. Therefore, in practical production, GABA can not only inhibit the stress response, but also promote feed intake. So that perfectly solved the effect of stress response and improved the production efficiency.
With the approaching of the summer and the prohibition of feeding antibiotics, feeding animals are bound to face a variety of stress, such as high humidity and high heat, no antibiotics in the feed, the increase of environmental microorganisms, and so on. GABA will be the best choice for you to improve the production efficiency.
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