Niacin, also known as nicotinic acid or vitamin PP, is one of the important B vitamins. Niacin deficiency in animals will result in stunted growth and reduced feed conversion. Numerous studies have shown that supplementation with niacin in monogastric or ruminant diets can improve their health and performance. This article mainly makes a review on the application of niacin in livestock and poultry production, and provides a reference for the further promotion and application of niacin in production practice.
1 Physicochemical properties of niacin
Nicotinic acid is a general term for biologically active pyridine-3-carboxylic acid and its derivatives, and nicotinamide is its main form in animals. Niacin and niacinamide are mainly prepared chemically. The molecular formula of niacin is C6H5NO2, and its properties are white to off-white powder, odorless or slightly smelly, slightly sour in taste, and its aqueous solution shows acidic reaction. The molecular formula of nicotinamide is C6H6N2O, and its properties are white crystalline powder or white granular powder, odorless or almost odorless, and bitter in taste.
2 Absorption and metabolism of niacin
Nicotinic acid exists mainly in the form of nicotinamide in animals, and nicotinamide forms coenzymes with ribose, phosphate and adenine, namely nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphoric acid (NADP). As cofactors, NAD and NADP enhance the activity of a large number of important enzymes that catalyze dehydrogenation and redox reactions. The biochemical reactions catalyzed by these enzymes are important for maintaining the cell structure and function of body tissues and promoting the synthesis of proteins, lipids and carbohydrates in the body. Metabolism plays an important role. Both niacin and niacinamide are absorbed in the body by diffusion, and the absorption sites are mainly in the stomach and upper small intestine; the metabolites are excreted through the urine. Niacin is absorbed directly in the rumen of ruminants. Erickson et al. (1990) found that the absorption rate of nicotinamide in the rumen of dairy cows was higher than that of nicotinic acid.
Niacin in animals mainly comes from natural feed and feed additives, and can also be synthesized through tryptophan conversion and digestive tract microorganisms. The content of niacin in natural feed is shown in Table 3. Although niacin is widely distributed in grain seeds and their by-products, most of the niacin is combined with polysaccharides, oligopeptides and glycopeptides through niacin bonds, making it difficult to be digested and utilized. Niacin in protein feed mainly exists in the form of free nicotinic acid, so it is easy to be absorbed and utilized. Niacin is added in a higher proportion in animal diets than other vitamins. Feed niacin supplements mainly include niacin and niacinamide. Harms et al. (1988) pointed out that two added forms of niacin had the same effect on dietary nutrient levels. After meeting the body’s protein synthesis needs, excess tryptophan in the body can be converted into niacin. Since most of the tryptophan is already used for growth or production, the conversion of tryptophan to niacin in the body is inefficient. Wu Miaozong and Cai Huiyi (1988) reported that theoretically 1.7 mg of tryptophan can be converted into 1 mg of niacin, 2% to 3% in chickens and piglets, and 0.5% in ducks. The rumen of ruminants can synthesize niacin, but the amount of niacin synthesis is regulated by the body’s metabolism. When synthetic niacin cannot meet the body’s metabolic and production needs, it must be supplemented in the diet.
4 Application of niacin in livestock and poultry production
At present, studies have shown that niacin has nutritional and physiological effects such as improving the production performance of livestock and poultry, enhancing disease resistance, improving meat quality and maintaining fur health. Real et al. (2002) reported that adding 13-55 mg/kg niacin to the corn-soybean meal-based diet of growing-finishing pigs can improve feed conversion efficiency; adding high levels of niacin can also reduce pork drip loss and pH, And improve pork meat color. Whitehead (2001) reported that adding 100 mg/kg of niacin to the diet of broiler chickens from 0 to 3 weeks can obtain optimal body weight; adding 100 mg/kg of niacin to the diet of broilers from 0 to 6 weeks can significantly Reduce the abdominal fat rate of broilers. Li Haiying et al. (2001) added 15, 30, and 45 mg/kg niacin to the diet of laying hens. The results showed that with the increase of niacin addition, the egg production, egg production rate and feed remuneration of laying hens increased significantly. Wu Chunyan et al. (2007) added nicotinic acid to the corn-meal type diet of meat ducks, and found that the requirement of niacin was 80 mg/kg for meat ducks aged 10 to 31 days to achieve ideal production performance. Xiangyang et al. (2008) showed that nicotinic acid can significantly improve the growth performance of juvenile carp, as well as the ability to deposit nutrients and digest and absorb; and use the broken line method to determine the requirement of niacin for juvenile carp to achieve optimal growth It is 31.12 mg/kg feed. The research results of Wu Fan et al. (2008) showed that adding niacin in the diet of juvenile grass carp can significantly improve the specific growth rate, weight gain rate and survival rate; The minimum requirement is 25.5 mg/kg feed. Yang Naide et al. (2010) added niacin 8 g/d to the diet of dairy cows, and found that the dry matter intake of dairy cows was significantly increased; the dry matter, organic matter, crude protein, crude fat, neutral detergent fiber, calcium and The apparent digestibility of phosphorus was also significantly improved. Sun Guojun et al. (2002) showed that adding 150 mg/kg niacin to sheep diets can significantly increase the average daily gain of lambs and reduce the feed-to-weight ratio.
5 Animal requirements for niacin
Announcement No. 1224 of the Ministry of Agriculture of my country stipulates that the recommended dosage of niacin in compound feed or total mixed diet (calculated as vitamins): 20-40 mg/kg for piglets, 20-30 mg/kg for growing and finishing pigs, Chicken 20-30 mg/kg, broiler chicken 30-40 mg/kg, dairy cow 50-60 mg/kg (concentrate supplement), fish and shrimp 20-200 mg/kg. The requirement of niacin for animals is mainly affected by factors such as genetic genes, animal breeds, health status, diet composition, processing and storage. Niacin deficiency usually results in skin, digestive tract, nervous system, and leg bone lesions in animals, typically with leg bone disease, pellagra, and black tongue. However, excessive intake of niacin may cause symptoms such as respiratory paralysis and fatty liver in animals. In animals, due to the interaction between niacin and tryptophan, tryptophan can be converted into niacin, so the animal’s requirement for niacin should also consider the level of tryptophan in the diet.
