In recent years, as an efficient, non-polluting, and non-residue feed additive, acidifiers have been listed as new-type green feed additives with prebiotics, enzyme preparations, flavoring agents, etc., and the application of feed acidifiers has become increasingly common. At present, acidifiers have been widely used in piglet feed, poultry feed, silage and other fields, and the effect is significant, but there are still some problems, such as the use of some acidifiers is still unstable, large dosage, high cost, made into premix Inconvenient feeding, some alkaline substances in feed often neutralize some of the added acid, absorption in the stomach is too fast, inhibit gastric acid secretion and normal development of gastric function, easy to absorb moisture and agglomerate, corrode processing machinery, transportation equipment, etc.
At present, there are many acidifier products on the domestic and foreign markets. According to different classification methods, they can be divided into: organic acids and inorganic acids, single acids and composite acids. The composite acid may be a composite organic acid or an organic and inorganic composite acid. Organic acids can be divided into macromolecular organic acids (lactic acid CH3CH (OH) COOH, molecular weight 90; citric acid C3H4-OH- (COOH) 3, molecular weight 192; fumaric acid COOHCH = CHCOOH, molecular weight 116; sorbic acid CH3CH = CHCH = CHCOOH, Molecular weight 112) and small molecule organic acid (formic acid CH2O2, molecular weight 46; acetic acid C2H4O2, molecular weight 60; propionic acid C3H6O2, molecular weight 74; butyric acid CH3 (CH2) 2COOH, molecular weight 88). Inorganic acids are mainly orthophosphoric acid. The quality of the acidifier product is not only closely related to its active ingredients and content, but also greatly affected by factors such as production technology. How to choose a good acidifier from many similar products is a headache for feed producers and animal producers.
The author believes that in order to choose good acidifier products, we must first have a clear understanding of the functions that acidifiers should have, and also have a clear and objective understanding of various products, so that we can be targeted.
1. The function of acidifier
1) Reduce feed pH and acid binding, promote gastric zymogen activation
The acid binding power of feed and raw materials is defined as the millimoles of hydrochloric acid required to reduce the pH value of 100g feed (raw material) to 4.0, and some people have defined it as the milligram amount of hydrochloric acid required to reduce the pH value of 1kg feed to 3.0. . For all young animals, the pH value of 100 g of feed reduced to the milligram equivalent of hydrochloric acid in the animal's stomach. The higher the acid binding power of the feed, the more free acid is bound in the stomach, and the more the gastric pH is increased. It is well known that some important zymogens in the stomach, such as pepsinogen, require gastric acid to be activated before they have catalytic activity. Feeds with high acid binding ability will affect the activation of zymogen, resulting in low digestive enzyme activity in the stomach, affecting the nutrition, especially protein digestion in the feed. In addition, when the pH in the stomach is high, the acidity in the stomach cannot meet the sterilization requirements, and microorganisms such as E. coli attached to the feed enter the small intestine and can reproduce in the small intestine (Sissons et al. 1989). In addition, undigested gastric contents provide good media conditions for E. coli growth.
Research shows that in addition to mineral raw materials, the acid binding capacity of feed ingredients has a high positive correlation with its protein content (R2> 0.8), that is, the raw materials with high protein content generally have high acid binding capacity. This has a great impact on young animals and high-performance animals, because these animals must contain higher protein in the feed to meet the needs of the body. The gastric acidity of young animals is often insufficient, and they are easily affected by high protein feeds with high acid binding capacity, which affects the animal's digestive and physiological functions, and leads to a combination of low feed intake and diarrhea. Disease, which seriously affects animal performance. In addition, mineral raw materials, especially calcium and phosphorus raw materials, have very high acid binding power. Due to the large amount of calcium-containing raw materials in the laying hen feed, it has a high acid binding ability, which seriously affects the digestion of the feed by the laying hens.
One of the main functions that feed acidifiers must have is to reduce feed pH and acid binding to increase digestive enzyme activity or activate some important enzymes. The ability of an acidulant to reduce pH and acid binding depends on the dissociation and molecular weight of the acid used. Inorganic acids have a high degree of dissociation and are fast, so they can quickly lower the pH value in feed and stomach. The dissociation degree of organic acids is relatively low, so the ability to lower the pH value is lower than that of inorganic acids, but the dissociation rate is slow, so the action time is longer.
Although inorganic acids have strong acidity and low added cost, research and practical applications show that the effects of inorganic acids are not as good as organic acids. On the one hand, it is worthwhile to reduce the pH of the stomach sharply, which will damage the gastric mucosa function and even burn the gastric mucosa, inhibit the gastric acid secretion and the normal development of gastric function; In addition, inorganic acids may also disrupt the electrolyte balance of the diet and cause a decline in feed intake, which seriously affects feed compensation and animal growth.
Macromolecular organic acids such as citric acid, lactic acid, fumaric acid, etc., because the molecular weight is relatively large, there are fewer hydrogen ions that can be dissociated per unit weight of acid molecules. Therefore, they are less effective at reducing pH and binding power of feed acids than small molecule organic acids. Some macromolecular organic acids are so-called polyacids, that is, in theory, an acid molecule can dissociate several hydrogen ions, but the dissociation of polyacids above the second level is very difficult, and the degree of dissociation is usually very small, so the actual Organic acids in the feed can only undergo first-order dissociation.
Therefore, for the purpose of reducing feed pH and acid binding power, small molecule organic acids work better than inorganic and macromolecular organic acids.