Animals can meet the needs of their own maintenance, growth and production by feeding to obtain the required nutrients. Increasing feed intake can better exert the production potential of animals. For pigs, it can maximize the meat production. And meat quality. However, under large-scale farming conditions, the actual feed intake of pigs is much lower than the ideal feed intake determined by the breed. The premise of large-scale farming cannot be changed. To improve the production performance of pigs, it is necessary to find ways to increase the actual feed intake of pigs and improve feed utilization. Improving feed palatability is a direct and effective way to make pigs like to eat feed, willing and active eating.
1 Feed palatability and animal feeding physiology
Palatability refers to the characteristics of the aroma, texture, taste and taste of the feed. It is the basis for a set of actions and reactions such as animal foraging and positioning to the final feeding. This is similar to human pursuit of food. Palatability reflects the extent to which the feed is accepted by the animal and alters the feed intake by affecting the appetite of the animal. Since the feed intake of animals can reflect the palatability of feed, then the study of the effect of palatability on feed utilization must first understand the feeding physiology of animals.
Animal feeding is a complex set of activities, including foraging, identification, localization, ingestion, and chewing and swallowing, and is regulated by the central nervous system. The regulation process is as follows: food emptying in the digestive tract of the animal - hunger - nerve conduction stimulation The hungry center of the hypothalamus - the efferent nerve conduction command - feeding - the gastrointestinal tract is full of food - satiety - through the afferent nerve conduction to the hypothalamic ventral medial center - through the efferent nerves to issue instructions - stop feeding. When the palatability of the feed is good, the pig's appetite is strong, which in turn leads to a larger food intake and improved feed utilization. When the palatability of the feed is poor, the appetite of the pig is not good, even if the intake is not large when starving. Feeds that are not eaten or eaten because of palatability cause a lot of waste and the feed utilization rate is very low.
2 affecting palatability factors
2.1 Flavor difference
The flavor of the feed is the most basic and intuitive factor in evaluating the palatability of the feed. Feed flavor mainly refers to the color, aroma and taste characteristics of the feed. In the processing of the compound feed, additives such as vitamins, minerals or pharmaceuticals may be added, and while exerting its nutritional and medicinal value, it also brings a bad taste, that is, poor palatability. As far as pig feed is concerned, many small feed enterprises use the poor-smelling crops or the waste of the food industry as feed ingredients in order to save costs. The feed produced is not good in flavor and cannot stimulate the pigs from the sense of sight, smell and taste. However, pigs rely mainly on taste and smell for foraging. Poor flavor and poor palatability directly lead to insufficient feed intake, low feed utilization, and affected production performance.
2.2 Anti-nutritional factors
Anti-nutritional factors are substances that cause the digestion, absorption and utilization of nutrients in feeds to decrease, causing adverse physiological reactions in humans and animals. Several typical representatives are tannic acid, protease inhibitors and plant lectins. In nature, plants contain a variety of anti-nutritional factors. These anti-nutritional factors are themselves a "defense mechanism" for plant bodies, which can protect plants and their seeds from pests, birds, etc. Also includes livestock and poultry. Today, 90% of the ingredients of factory-based compound feed are plant-based ingredients, while plant-based ingredients usually contain one or more anti-nutritional factors.
The bitterness of tannins will directly reduce the feeding habits of animals. At the same time, tannins also form indigestible complexes with proteins, carbohydrates and other ingredients in the feed, reducing protein digestibility. Tannins directly cause a decrease in the taste of pigs. When the pigs are forced to eat, the combination of tannins and feed proteins reduces the protein digestibility. Therefore, on the one hand, the intake of food is reduced, and on the other hand, the digestion of protein is blocked, and the combined effect of the two aspects leads to low utilization rate of pig feed.
Protease inhibitors are mainly found in legumes and can inhibit the action of various proteases such as trypsin, pepsin and chymotrypsin. There are many types of such factors, among which trypsin inhibitor (KTI) and chymotrypsin inhibitor (BBI) are the most important. Trypsin inhibitor combines with trypsin in intestinal fluid to form an inactive complex, which reduces trypsin activity and reduces protein digestibility. In addition, chymotrypsin inhibitor causes pancreatic hypertrophy and digestive disorders. And disorders, animal growth is blocked. In the case of pigs, the interaction of these two protease inhibitors, on the one hand, destroys the digestive function, on the other hand, reduces the digestive enzyme activity, thereby causing a decrease in feed digestion and utilization, and the growth and production performance of the pig are affected.
Lectins are proteins that are produced by plant seeds and animals that bind to specific monosaccharides or oligosaccharides. It has been reported that most of the lectins are not degraded when they pass through the digestive tract, and can bind to the receptors of epithelial cells. The two causes cause changes in the morphology and metabolism of the intestinal cells, which in turn affects the digestion and absorption functions of the intestinal tract. Therefore, when the pigs ingest the plant-based feed containing the lectin, the digestion of the feed is affected, and the utilization rate is lowered. In addition to the above three types, there are other anti-nutritional factors such as saponins, cellulose, lignin, and phytic acid. Saponins can weaken the activity of digestive and metabolizing enzymes; cellulose and lignin are difficult to digest, which will hinder the absorption of normal nutrients; phytic acid will combine with proteins and trace elements to form complexes and inhibit the absorption of trace elements.
2.3 Metamorphic
Feed deterioration refers to the process of processing the feed before it is fed to the animal. Due to the storage and transportation, the microbial growth and nutrients in the feed are changed. The main situation is mildew and oxidation. According to the Food and Agriculture Organization of the United Nations (FAO), about 25% of the world's cereals are contaminated with mycotoxins to varying degrees, causing millions of dollars in damage each year, which has a great impact on crop producers, animal breeders and food producers. . The molds of contaminated feed mainly include Aspergillus, Penicillin, Scythe, and Mucor, followed by Cladosporium, Streptomyces, Codromyces, Pythium, Paecilomyces, Trichoderma, Rhizopus and so on. Mildewed feed has significant changes compared with normal feed, mainly due to agglomeration, heat, discoloration, odor, powdery and so on. The growth of mycotoxins is closely related to moisture and temperature. It has been pointed out that when the feed moisture is lower than 12.5%, it is not easy to breed mold. When it reaches 13% to 16%, it can cause mold to multiply. When the moisture is above 16%, the addition of anti-fungal agent is also ineffective. When the temperature is lower than 10 °C, mold is not easily generated, and when the temperature is between 28 ° C and 38 ° C, the bacterial population is generated in a large amount. Mildewed feed can cause many diseases in pigs. The main situation is: poisoned piglets have acute central nervous system symptoms and will die in a short period of time; large pigs have slow onset, initial manifestations of poor appetite, erythema in many skins, and loss of appetite in the later stage. Abdominal pain, blood in the stool, and finally death; pregnant sows with stillbirth, high abortion rate, abnormal estrus after childbirth; lactating sows showed progressive refusal to eat, showing continuous estrus or prolonged estrus cycle, affecting the survival rate of lactating suckling pigs.
There are many reasons for the oxidation of feed. The main problem is the oxidative rancidity of unsaturated fatty acids and the production of unpleasant odors. It has been reported that the products of oxidative rancidity of feed such as aldehydes, ketones, acids, esters, etc. have adverse effects on animals, mainly as follows: (1) bad odor, animal refusal, slower body weight gain, low feed conversion ratio (2) feed heat agglomeration, accelerate mold, cellulose is also destroyed; (3) visceral system, digestive system, circulatory system, etc.; (4) animal immunity is reduced, disease resistance is weak; (5) Affects cell structure, function, and stability of biofilms.
2.4 Unreasonable processing
The feed is processed from raw materials into finished products, which undergo a series of processes such as crushing, stirring and cooking. The physical form, chemical structure and nutritional composition of the feed ingredients have also changed accordingly. According to different purposes, the feed can be processed into powder, granules, flakes and the like. Earlier experiments showed that the digestion rate of the cooked pellets in the pigs was lower than that of the cooked powdered feed, while the conventional powdery feeds had a significantly lower digestibility than the cooked powdered feeds. The same feed ingredients, the same formula, are made in different shapes, and the palatability of the feed is different. The pulverized grain size of pig feed is relatively fine. The too coarse feed has poor palatability, affecting the digestibility and reducing the production performance of pigs. However, if the feed is too fine, pigs will be susceptible to stomach ulcers and increase production costs.
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