1, chicken

　　Chickens have relatively short digestive tract and weak intestinal mucosal barrier. Under intensive farming conditions, compared with long digestive tract animals, they are more vulnerable to harmful microorganisms, leading to the occurrence of various diseases. The use of feed additives is one of the effective means to prevent intestinal diseases and improve the performance of Broilers and layers. The growth of broilers is fast and the intensive production is greatly affected by the environment. The application of feed additives can improve the balance of intestinal flora, reduce the incidence and mortality of intestinal diseases, increase the output weight, reduce the feed-meat ratio, and reduce the emission of harmful gases such as ammonia and hydrogen sulfide in chicken houses, and improve the quality of products. The application of feed additives in laying hen breeding can not only prevent and cure diseases, improve production performance and feed remuneration, but also improve egg quality. The results showed that the addition of feed additives in the diet of laying hens could increase the Hardy's unit of eggs, reduce the cholesterol content of eggs, and improve the thickness of eggshells and reduce the soft-shelled eggs.

2, pig

　　At present, research and application show that feed additives have achieved good results in the breeding of piglets, sows and fattening pigs. Adding feed additives to piglet diets can promote intestinal development, improve intestinal health, reduce diarrhea rate, and increase growth rate and feed conversion rate of piglets. For lactating piglets, the addition of feed additives can help to establish the dominant microflora of probiotics; for weaned piglets, it can improve the adverse effects of diarrhea and growth retardation caused by self-digestive enzyme secretion, dietary antigenicity and other factors. The results showed that the use of feed additives in sow diets could improve intestinal health, immunity and reproductive performance of sows. After adding feed additives, the ability of regulating bacterial balance in gastrointestinal tract can be improved, feed intake of sows during lactation period can be increased, weight loss can be inhibited, fat and protein content in sows'milk can be increased, survival rate of weaned piglets and weight of weaned piglets can be increased. Adding feed additives to the diet of fattening pigs can increase feed intake and feed conversion rate, improve health status, shorten fattening period, and improve quality and reduce environmental pollution. The results showed that dietary additives could reduce diarrhea rate, improve immunity, feed intake and digestibility of fattening pigs, thereby increasing the utilization rate of diet and reducing feed-meat ratio. Moreover, feed additives can promote the increase of intramuscular fat and essential fatty acid content, and improve the quality of pork. [2]

3. Ruminants

　　The results showed that feed additives could improve the growth rate of meat ruminants such as mutton sheep and beef cattle, increase the net meat percentage of carcass and improve meat quality. Feed additives can increase milk yield, prolong milk production peak, increase milk fat rate, reduce the number of somatic cells in milk and improve milk composition in milk ruminants. It also plays a role in preventing mastitis and reproductive diseases. For calves whose digestive tract is not well developed, the use of additives can promote the establishment of gastrointestinal flora, regulate the balance of flora, and reduce the incidence of diarrhea in calves. In addition, the use of feed additives can promote the weight gain of calves.

4. Aquatic products

　　The application of feed additives in aquatic products is reflected in two aspects: bait and water purification. Feed additives can improve the microecological balance of aquatic animals, promote growth and development, play a role in disease prevention and improvement of production performance. Probiotics can be planted in the intestinal tract of fish, promote the growth and development of fish, and improve disease resistance. Feed additives can reduce the incidence of shrimp and increase the survival rate and yield. Feed additives can be used as immune stimulants and adjuvants for aquatic animals to promote the development of immune organs, improve the level of humoral immunity and improve immune function. This effect has been verified in many aquatic animals. Photosynthetic bacteria and nitrifying bacteria in feed additives can consume organic substances in water, remove ammonia nitrogen, hydrogen sulfide, nitrite nitrogen and so on. They are important beneficial microorganisms used to improve aquaculture environment. They have obtained good application results in aquaculture of shrimp, flounder and other aquatic animals.