Progress in the application of silage additives
Abstract: Silage is widely used in the production of ruminants due to its high nutritional value, low cost and no restrictions on seasons and climate. However, it is involved in the process of production, including the degradation of substances and the fermentation of probiotics. Silage additives are often used in the process. Silage additives can prevent silage, promote fermentation and improve palatability. Silage additives can be divided into: inhibitory additives, promotional additives, nutritional additives according to their functions. The author reviews the types, functions, application effects and future development directions of silage additives in recent years.
Key words: silage; additives; effect
CLC number: S816.7 Document code: A Article ID: 1671-7236 (2012) 08-0124-04
Silage is a technology for storing fresh feed and green grass forage nutrients by anaerobic fermentation in a closed environment to convert sugar in crop straw into lactic acid, produce an acidic environment, inhibit and kill the reproduction of various harmful microorganisms. (Weddell et al., 1991); this kind of feed basically retains the characteristics of green, succulent and nutrient-rich, and the source of silage is rich, and the color and leaves of straw can be preserved during production. Silage is soft and juicy, sweet and sour, aromatic and palatable. It can promote the secretion of digestive glands and improve the digestibility of feed. Its preparation method is simple and free from climate and seasonal restrictions, so it is widely used. However, the process of silage production involves the degradation of some nutrients in the feed, such as the degradation of plant cell walls, and the fermentation of microorganisms, which will directly affect the quality of silage. Therefore, the use of additives to silage is often used in the processing of silage. The process is regulated. Silage additives can be used to improve silage nutrients, can effectively promote silage fermentation, improve silage quality (increased aerobic stability), and improve the palatability of feed (Henderson, 1993).
1. Types and characteristics of silage additives
There are many types of silage additives and there are many classification methods. Currently used silage additives are classified into three categories according to their effects.
1 Inhibitory additive: It can inhibit the aerobic microbial activity and the fermentation of undesirable microorganisms during silage fermentation, thus effectively preventing silage corruption, and finally aiming to preserve the nutritional value of feed. Commonly used inhibitory additives are mainly preservatives, such as formic acid, acetic acid, propionic acid and other inorganic acid salts of formaldehyde and organic acids (Hiraoka et al., 2010); 2 Promoting additives: These additives can promote the solubility of lactic acid bacteria. Sugar fermentation, mainly lactic acid bacteria, enzyme preparations, etc.; 3 nutritional additives: can properly change the palatability of feed, while also increasing the nutrition of silage, such as molasses, salt, urea and so on.
2. The application effect of various silage additives
2.1 Inhibitory Additives
2.1.1 Formic acid, also known as formic acid, has strong reducing ability and is an inhibitory additive commonly used in foreign countries. Sarah et al. (1992) added formic acid to silage, which can significantly reduce the pH, non-protein nitrogen and ammonia nitrogen concentration of silage, and this treatment can also effectively reduce the degradation rate of silage protein. Nadeau et al. (2000) showed that formic acid not only reduced silage pH (pH < 4.2) and increased acetic acid concentration, but also significantly increased the concentration of lactic acid, effectively inhibiting the growth and reproduction of undesirable microorganisms. When the amount of formic acid added is 5% of the fresh silage raw material, more soluble carbohydrates and crude protein can be retained, and the yield of acetic acid in the silage can be increased (Ak-su et al., 2006). The addition of formic acid to the silage can also increase the neutral detergent fiber content and dry matter preservation rate, and can significantly reduce the silage nitrate content and effectively improve the fermentation quality of silage (Qin Ligang et al., 2010).
2.1.2 acetic acid and propionic acid
Acetic acid as an inhibitory additive not only inhibits the growth of undesirable microorganisms, but also effectively increases the aerobic stability of silage (Danner et al., 2003), and also improves the fermentation quality of silage. Propionic acid is weaker than formic acid and other inorganic acids, but it is still an effective antifungal agent, which has a good effect in inhibiting aerobic spoilage of silage, and propionic acid can significantly improve the aerobic stability of silage ( Kung et al., 2000, 2004). The results showed that the addition of propionic acid was superior to acetic acid in increasing silage lactic acid content, reducing silage pH and ammonia nitrogen concentration (Guo Yanping et al., 2010). In general, when the amount of propionic acid added is 0.5% to 0.6% of the silage raw material, the growth of undesirable microorganisms can be effectively suppressed, and the spoilage of the silage can be effectively prevented (Mills et al., 2002).
2.1.3 Formaldehyde
Formaldehyde is a commonly used disinfectant at home and abroad, and is also an inhibitory starter. Formaldehyde can inhibit the activity of various microorganisms during silage, improve the odor, structure and color of silage, and can effectively prevent the degradation of crude protein in silage (Zhang Shupan et al., 2009); Yang Fuyu et al. (2004) mixed formic acid with formaldehyde. The agent is used for silage fermentation, which can reduce the ammonia nitrogen content of silage, ensure more soluble carbohydrates and crude protein, and can significantly improve and improve the fermentation quality of silage, which is basically the same as the research results of Zhang Shupan et al. (2009). . The effect of formic acid mixed with formaldehyde for silage was significantly higher than that of formic acid alone. The results of foreign studies showed that the daily weight gain and milk production of dairy cows increased by 67% and 5%, respectively, after silage forage treated with mixed additives of formic acid and formaldehyde (Weddell et al., 1991).
Recently, Knicky et al. (2011) found that sodium benzoate, potassium sorbate and sodium nitrite mixed additives can improve the quality of silage fermentation of various forage crops, and can significantly reduce silage pH, ammonia nitrogen, and Acid and ethanol concentrations and the number of Clostridium can also reduce dry matter losses. Therefore, sodium benzoate, potassium sorbate, etc. can also be used as a good inhibitor of silage.
2.2 Promoting Additives
2.2.1 Lactic acid bacteria
Adding lactic acid bacteria during silage can effectively reduce the pH in silage and increase the yield of lactic acid, so as to obtain the advantage of early lactic acid fermentation and effectively inhibit the reproduction of harmful microorganisms (Kung et al., 2004). The ability of lactic acid bacteria to produce lactic acid by fermenting sugar can classify lactic acid bacteria into two types, one is homo-fermentative lactic acid bacteria, such as Lactobacillus plantarum, Pediococcus pentosaceus, and the other is heterogeneous. Hetero-fermentative lactic acid bacteria, such as Lactobacillus brevisii (Keles et al., 2011).
The results show that lactic acid bacteria can reduce the production of yeasts and molds, effectively inhibit the growth of harmful bacteria and other microorganisms such as Enterococcus and Klebsiella pneumoniae (Zhang et al., 2009; Filya et al., 2006), significantly increasing acetic acid in silage and The content of propionic acid (Kung et al., 2007) and effective improvement of aerobic stability of silage (Tabacco et al., 2011). Kleinschmit et al. (2006) studied corn and grass silage with Lactobacillus brevis (LB2) containing less than 100,000 CFU/g (LB1) and greater than 100,000 CFU/g, respectively, and showed that both treatments reduced corn silage. The concentration of lactic acid did not decrease the concentration of lactic acid in the silage of the grass, and both treatments increased the content of corn silage acetic acid, but had no effect on the content of propionic acid, ammonia nitrogen and water-soluble carbohydrate. The aerobic stability of LB2 treated silage corn was significantly better than that of LB1 and the control group. Zhang Tao et al (2009) combined the Lactobacillus brevis and Lactobacillus plantarum for silage, compared with the effect of silage alone, the results showed that the combined silage effect was better than the silage alone, which can effectively reduce the pH. The ammonia nitrogen concentration can produce more lactic acid, especially the aerobic stability of silage. Schmidt et al. (2010) studied the silage effect of whole plant corn with Lactobacillus brevis (LB) and mixed bacteria of Lactobacillus brevis and Pediococcus pentosaceus (LBPP). The results showed that corn silage treated with LB and LBPP The content of lactic acid and propylene glycol was significantly higher than that of the control group. The amount of ethanol and yeast was significantly lower than that of the control group. The aerobic stability of corn silage treated with LBPP was better than that of LB alone. However, some studies have shown that the fermentation effect of hay silage treated with heterogeneous lactic acid bacteria (heLAB) and homogenous lactic acid bacteria ho LAB mixed bacteria (he+hoLAB) is similar to that of homologous Lactobacillus (hoLAB) alone. The use of heterogeneous lactic acid bacteria (heLAB) is slightly worse (Conaghand et al., 2010).
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