The nutritional requirements of crab and the production of compound feed
1 The nutritional needs of crabs 1.1 Proteins and Amino Acids The crude protein content of formulated feed for crabs from the juvenile stage to the growing stage was 45% to 28%. The crude protein made from white fish meal, cakes, gluten meal, shrimp meal, and egg yolk powder is used as the main raw material for 45% of the crabs. 250 heads, respectively, fed to Z1 ~ Z5 larvae, their larvae after feeding the feces rate is high, abnormal neat, mink time is short, the survival rate is high. After the crabs went out of the pond, there were few residual baits at the bottom of the pond, and 42% of the compound feed (opening material) was used to feed the big eye larvae to the V juvenile crabs. After about 1 month of feeding, the juvenile crabs grew quickly and lively. For health, the survival rate is about 50%, and the feed coefficient is about 0.8. The content of crude protein in compound feeds during the crab growing season ranged from 28% to 36%. Under this condition, the individual crabs that were fed out were larger and had fewer diseases, and most of the farmers were profitable. According to the physiological characteristics of river crabs, the early temperature of the crabs is suitable. It can feed 36% crude protein compound feed. In the middle water temperature, the crab grows relatively slowly. It can feed 28% crude protein compound feed and combine with some aquatic plants and grains. Later, the water temperature is more suitable for the growth of crabs. At this time, the crabs ingest large amounts of food. They reserve nutrition for the winter and can feed 33% of the compound feed. Therefore, the crabs caught in the late autumn and early winter are crab fat paste yellow. This feeding pattern is also in line with the principle of "two-nose fine intermediate" for feeding crabs. The need of protein for crabs is in essence the need for amino acids. The crabs digest the proteins obtained from the feed into peptides, amino acids and other small molecule compounds before they finally transform into crab tissues. The essential amino acids required for crabs are basically similar to shrimps, namely threonine, valine, leucine, isoleucine, tryptophan, methionine, phenylalanine, histidine, lysine and Arginine 10 species. The suitable requirements for various essential amino acids in crabs have not been reported yet. The shrimps were mainly used in the design of formulas. The growth effect of crabs on free amino acids was not significant. In order to complement amino acids in compound feeds and meet the needs of growth and development of crabs as much as possible, under the premise of ensuring the quality of feed ingredients, as much as possible when using raw materials, various types of raw materials, such as fishmeal, various types of cakes, and yeast, should be used. Bran and so on. However, when using pancakes, it is important to note that although peanut aphids can be used in large amounts in river crab diet, they are prone to aflatoxin, and care should be taken in storage and quality; cottonseeds contain gossypol, and rapeseed meal contains mustard tincture. Such toxic substances, but also bitter taste, poor palatability for crabs, therefore, the amount added in the feed should not exceed 7%. 1.2 Lipids Adding a certain amount of phospholipids in the feed can increase the survival rate of juvenile crabs and accelerate molting. The appropriate amount of phospholipids in feeds is 1% to 1.5%. 1.3 Crude fiber Crude fiber is generally not used by crabs, but it is necessary to maintain the health of crabs. The appropriate amount of crude fiber can stimulate the secretion of digestive enzymes, promote gastrointestinal motility and digestion and absorption of protein and other nutrients. Appropriate crude fiber content is from 4% to 5% for the big eye larvae to young crabs and 6% to 7% for the growing period. 1.4 Minerals and Vitamins There are very few reports on the demand for minerals and vitamins in river crabs. In the production practice, the content of calcium and phosphorus in the compound feed is 1.5%-2.0% of calcium before young crab, 1.8%-2.5% of phosphorus, and 1:1.2 of calcium and phosphorus ratio. The calcium of crab is 1.2. % ~ 2.0%, phosphorus is 1.0% ~ 1.8%, calcium, phosphorus ratio is about 1:0.9. See Table 2 for daily usage of minerals and vitamins in crab compound feed. Due to the special requirements of the physiology and growth of oyster shells, crabs have a higher demand for vitamins, choline and inositol. Vitamin C can participate in the synthesis of chitin in the crab body, so that the crust hardening, improve the survival rate and growth rate of the clam shell, and can improve the disease resistance of the crab; vitamin D3 to promote the absorption of calcium and phosphorus in the intestine and in Deposition in the bone base plays an important role. Vitamins are susceptible to high temperatures and are destroyed during granulation. Conditional units can be sprayed. 2 key issues in making crab feed 2.1 raw material selection In the livestock and poultry feed formula, corn is one of the largest raw materials, so it is usually called animal feed for energy feed. However, the ability of crabs to metabolize sugar is low, and the demand for protein is high. Feed protein levels, animal and plant protein ratios all directly affect crab feed intake, growth rate, and feed utilization. In addition, crabs and fish are temperature-changing animals, and their body temperature changes with changes in water temperature. The ammonia nitrogen is the waste product of protein metabolism. This metabolic form consumes much less energy than animal and poultry metabolic waste, mainly urea and uric acid. Therefore, crabs The use of basically protein, also known as crab feed for protein feed, which is very different from livestock and poultry feed. 2.2 raw material grinding granularity The digestive organs of crabs are simple and short, and the ratio of digestive tract length to body length is much smaller than that of livestock. Digestive glands are not well-developed. All kinds of digestive enzymes have low activity due to low body temperature. The number and species of digestive bacteria in the intestine are small, and the time for food to stay in the digestive tract is significantly shorter than that of livestock and poultry. Therefore, in the processing of feed, the raw material for crab feed needs to have a finer crushed particle size. Under normal circumstances, the raw material fineness of ordinary fish feed requires all 40 meshes, while the crab feed requires more than 95% of the 80 mesh. Finer particle size will help improve the digestion and absorption of nutrients by crabs, and it will also help improve the mixing uniformity of the feed and the rate of pellet formation, and improve the stability of feed pellets in water. 2.3 Feeding methods and feed dispersion time Feeding methods of livestock and poultry are chewing or foraging, and there is no special requirement on the shape of feed. Fish is devoured. As long as the size of feed is adapted to the caliber of fish, the feed can be fed by fish after entering the water, during the time of feed dispersion. Not too particular about the normal requirements of the dissolution time in the water not less than 0.5h; while the crab is foraging, using two large claws to feed the compound feed to the chewing machine, and then into the mouth, therefore, It is required that the dissolution time of the crab compound feed in water must be more than 12 hours. To achieve appropriate water stability, the following measures can be taken: 1 increase the amount of raw materials containing starch and more, such as sub-powder, wheat, etc., in the granulation process, the starch gelatinization, resulting in increased water stability of the feed; 2 Add Non-nutritive special adhesives, currently the most used are high polymer adhesives, such as polyurea formaldehyde, but this adhesive is more toxic after use, it should be added in the specified amount; 3 use reasonable processing Process. The crab material needs high gelatinization degree and water stability. For this purpose, firstly, the compression ratio of the ring die is increased, which can be more than 20, so that the extrusion strength of the raw material in the ring die is increased, and the pressure time is longer. Can improve the stability of the particles in water; Second, the use of three conditioning machine, tempering temperature above 90 °C, adequate conditioning to starch gelatinization, protein denaturation, increased feed digestibility and water resistance. In addition, the post-curing process can be used to allow the hot particles that have just been released from the mold to continue under high temperature and high humidity for a period of time to further gelatinize the starch. The pellet feed is kept in the post-curing device for 12 minutes, and the starch gelatinization rate can be increased from 33.3% to 53%. %. After ripening pellet feed can improve water resistance. 2.4 Additives In addition to the use of adhesives for improving the stability of water, crab crab feed needs to stimulate animal appetite, increase feed intake, promote growth and use attractant; antioxidants are also needed to prevent oxidation of oils. There is no large amount of fish in the crabs, and the amount of feed is relatively small. The feed needs to be stored for a long time. To prevent mildew, feed moisture must be controlled at 11% in addition to the addition of the antifungal agent during the high temperature and rainy season. Within. 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Lipids are energy substances necessary for the growth and development of crabs. They provide nutrients such as fatty acids, cholesterol, and phospholipids needed for growth of crabs, as well as absorption of fat-soluble vitamins. Among fatty acids in crabs, unsaturated fatty acids account for a large proportion of total fatty acids, approximately 70% to 83%, of which polyenoic fatty acids, especially eicosapentaenoic acid [20:5(n-3), EPA] and II Docosahexaenoic acid [22:6(n-3), DHA] accounts for a very high proportion. In addition, the saturated fatty acid content of juvenile crabs was significantly higher than that of adult crabs, and monoene fatty acid content was significantly lower than that of adult crabs. The dicosatetraenoic acid of juvenile crabs was more than two times higher than that of adult crabs. Therefore, the crude fat content of larvae to juvenile crabs is designed to be 6% to 8%, and the crab stage is 3% to 6%. Fish oil contains a variety of highly unsaturated fatty acids and some unknown growth factors, is suitable for the addition of the crab feed.
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