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Like other farmed animals, in order to maintain normal life activities and meet the needs of the body's growth and development, the Chinese turtle needs to ingest food from the outside world and obtain protein, lipids, carbohydrates, vitamins, minerals and other nutrients.
However, the Chinese turtle is a reptile, and there are obvious differences in the nutritional needs of fish and terrestrial animals, such as turtles have higher protein and lipid requirements than fish;
In terms of energy supply, terrestrial animals first digest carbohydrates to supply energy, followed by digestion of lipids and proteins, while turtles are the first to digest lipids to supply energy, followed by digestion of proteins and carbohydrates, turtles have a low utilization rate of carbohydrates; in the demand for inorganic salts is also different from fish and land animals.
First, protein
Protein is the main component of the animal body, is the animal growth and development and maintenance of life activities of the essential nutrients, for the growth and development of turtles is essential, feed can not be missing protein.
In general, the protein demand of Chinese turtles gradually decreases with the growth of individuals, and is affected by many factors such as protein quality, lipid content, raw material crushing particle size, water quality conditions, and breeding patterns in feed.
The protein requirements of chinese turtles have the following characteristics:
1. High demand
The protein demand of turtles is 43% to 50%, when the protein level in the feed reaches a certain limit, if it continues to increase, not only can not improve the growth rate of turtles, but also often harmful.
According to the results of Japanese scholars' research on the protein demand of juvenile turtles, when the protein level in the feed is less than 50% or more, the weight gain rate and feed efficiency of turtles (the weight gain of turtles as a percentage of feed intake) are poor, and when they exceed 60%, they are worse.
2. Animal protein is the mainstay
According to the dietary requirements of turtles, animal protein feed should be the mainstay, and plant protein feed can be appropriately matched.
According to the research results of Ren Zebiao et al. (1997), when the animal-plant protein ratio is 6:1, the weight gain rate, survival rate and bait coefficient of turtles are the best. In animal protein feed, the amino acid composition of imported white fish meal is comprehensive and reasonable, and its fishy taste has an attractive and promoting feeding effect on turtles, and the feeding effect is the best.
3. Low utilization of plant-based proteins
Turtles have a low ability to utilize plant-based proteins, and adding too much will affect the growth of turtles.
Some research data show that under the condition of basically the same crude protein level, with the increase of the proportion of plant protein feed (such as soybean meal), the weight gain rate of turtles is significantly reduced, and the bait coefficient (the ratio of feed amount fed to turtles and total net weight gain) increases significantly;
When the plant protein content is within 15%, turtles can eat normally and grow well, growth is blocked when more than 15%, and more than 30% are seriously uncomfortable, and the amount of food intake is reduced, and even food intake is stopped.
4. The demand for protein is different at different stages of development
In general, the younger the age of turtles, the more vigorous the metabolism, the higher the weight gain rate, the higher the demand for protein in the feed, the demand for protein in the juvenile turtle stage is higher than that of young turtles, young turtles are higher than adult turtles, and the demand of brooding turtles due to special physiological needs is between young turtles and adult turtles.
It is generally believed that under the conditions of moderate growth temperature, the protein demand of juvenile turtles is 45% to 55%, the protein demand of young turtles is 40% to 45%, the protein demand of adult turtles is 35% to 40%, and the protein demand of turtle broodors is 38% to 43%.
Therefore, understanding the characteristics of protein demand at different stages of development of Chinese turtles, we can design a more reasonable feed formula to fully meet the physiological needs of turtles, and maximize feed efficiency and optimal breeding effect.
The amount of protein required by Chinese turtles is essentially the amount of essential amino acids, so the feeding effect of feed depends not only on the content of protein in the feed, but more importantly on its amino acid composition.
When the amino acid composition of the protein in the feed is similar to the amino acid model of the Chinese turtle muscle, the amino acid needs of turtle can be better met, and the balance mode of the essential amino acids in the growth stage of turtle feed is: threonine 2.61%, valine 2.70%, methionine 1.37%, isoleucine 2.57%, leucine 4.51%, phenylalanine 2.51%, lysine 3.94%, histidine 1.39%, arginine 3.37%.
In the design of feed formula, not only the content of protein, but also the composition of amino acids, to try to choose turtles like to eat and easy to digest and absorb protein feed.
2. Lipids
Lipids, commonly known as lipids, are important sources of energy and essential fatty acids, as well as carriers of fat-soluble vitamins, in which phospholipids play an important role in the structure of cell membranes, and cholesterol is a precursor to various steroid hormones that have an important physiological role.
The demand for lipids in Chinese turtles has the following characteristics:
1. High demand for lipids
Turtles require more fat than general aquatic animals, so it is necessary to add an appropriate amount of lipids to turtle feed, which can not only increase energy sources, but also provide the fatty acids needed by turtles, and improve the palatability of feed.
According to research, the appropriate content of fat in the feed of juvenile turtles is about 9%, and the appropriate content of fat in turtle feed during the growth period is about 5%. However, excessive lipid content can cause increased fat in turtles, and even cause lipid metabolism disorders.
2. High digestion and absorption rate of lipids
Turtles have a high digestion and absorption rate of lipids, up to more than 80%, so the energy substances used as feed with fats are more ideal.
3. High demand for unsaturated fatty acids
Because turtles themselves cannot synthesize long-chain polyene unsaturated fatty acids, the demand for unsaturated fatty acids in the feed is high.
4. High utilization rate of lipids with low melting point
Turtles are in a liquid state at room temperature than lipids in a solid state at room temperature, and oil should be added to the turtle feed.
In the process of transportation and storage, long-chain polyene unsaturated fatty acids are very easy to oxidize, producing toxic substances, so the general feed manufacturers strictly control the lipid content in the feed does not exceed 5%, farms (or households) in the feeding of compound feed, you can mix a certain amount of animal oil or vegetable oil, the amount of addition to 2% to 5% is appropriate, it is best to add fish oil, because fish oil is rich in linoleic acid, followed by corn oil and other vegetable oils.
Third, carbohydrates
Carbohydrates are the main components of plant-based feeds and are the cheapest and most readily available energy substances in feeds, and are often divided into nitrogen-free extracts and crude fibers in nutrition.
Carbohydrates are broken down into simple sugars in the animal digestive tract and absorbed, which not only provides energy, makes up the body's components, but also saves feed protein and acts as a binder for feed.
If carbohydrates are not supplied enough, turtles need to break down more protein in their feed to meet their energy needs.
However, the use of carbohydrates by turtles is poor, the digestibility is about 65%, and its energy supply is mainly derived from lipids and proteins, so the carbohydrate content in turtle feed should not be too high, otherwise it will affect the growth and feed conversion rate, and even affect the health of turtles, the appropriate content of carbohydrates in turtle feed is generally 20% to 28%.
In the Chinese turtle compound feed, the addition of an appropriate amount of carbohydrates can improve the utilization rate of turtles on feed protein, promote growth, after long-term experiments have proved that when the content of carbohydrates is between 20% and 28%, the utilization rate of turtles on protein is higher, and the feed conversion rate is also higher.
Young turtles require slightly less carbohydrates than adult turtles. Yoshiichi Kawasaki (1986) found that in α-starch, dextrin, sucrose, cellulose and other carbohydrates, turtles have the best use effect on α-starch, with the weight gain rate being the highest at α-starch addition of 20%, and the feed efficiency being the highest at α-starch by 30%.
According to Xu Xuyang et al. (1991), the appropriate amount of α-starch required by adult turtles is 22.73% to 25.27%, and the amount of cellulose added should be less than 10%.
Crude fiber is generally not directly used by Chinese turtles, but it is a substance necessary for maintaining health.
The appropriate amount of crude fiber in the feed can stimulate the secretion of digestive enzymes, which helps the intestinal peristalsis and the digestion and absorption of nutrients such as protein, but too much added will affect the growth of turtles, and it is generally believed that the content of crude fiber in turtle compound feed should not exceed 5%.
Juvenile turtles require less crude fiber, and as the turtle grows, the content of crude fiber in the feed gradually increases. Fishmeal contains almost no cellulose, and the cellulose in the feed comes from plant-based raw materials.
Fourth, vitamins
Vitamins are essential to maintain the normal physiological function of the animal body is a class of small molecule organic compounds, is the basic component of coenzymes and auxiliary groups, involved in the biochemical reaction and metabolism in the body, although the amount is small, but the role is larger, if the lack of vitamins in animals will make the activity of certain enzymes out of balance, resulting in metabolic disorders, affecting the normal function of some organs of the body.
Animals generally cannot synthesize vitamins in the body or the amount of synthesis is very small, which needs to be obtained from feed.
Turtles grow slowly when they are deficient in vitamins and develop various diseases. According to Yoshiichi Kawasaki (1986), from the perspective of growth rate, when vitamin B6, niacin and vitamin B12 are deficient, turtles have stunted growth and development, decreased appetite and decreased fecundity, but when there is a deficiency of folic acid, vitamin B2 and pantothenic acid, the impact on growth is not large.
When vitamin E is deficient, juvenile turtles are prone to fungal diseases, poor sperm motility, low egg laying, poor fertilization rate of eggs, muscle malnutrition in adult turtles, and reduced protein content in muscles.
The vitamin demand of turtles is not only affected by weight, age, growth rate, environmental factors, but also by the interrelationship between nutrients, and too low or too high vitamins in the feed will bring harm to the health and function of the turtle.
In order to promote the rapid growth of turtles, adding vitamin B1, vitamin B2, vitamin B6, vitamin B12, vitamin C, folic acid, calcium pantothenate, niacin and other 11 kinds of water-soluble vitamins and vitamin A, vitamin D, vitamin E, vitamin K and other 11 kinds of fat-soluble vitamins are essential, and some fresh bait can also be added. The amount of vitamins added to turtle feed can be referred to Table 6-1.
5. Minerals
Minerals, also known as inorganic salts, are essential substances for maintaining the normal physiological functions of the animal body, and are necessary components for the composition of animal bone tissue, which can not only regulate the osmotic pressure balance in the animal body, but also promote animal growth and development and improve feed efficiency.
Although the Chinese turtle can absorb a small amount of minerals from the aquatic environment, this does not meet the needs of growth and development, and must be provided by feed.
The minerals required by turtles include calcium, phosphorus, potassium, sodium, sulfur, chlorine, magnesium and other constant elements and trace elements such as iron, copper, zinc, manganese, cobalt, selenium, iodine, and chromium, but the appropriate amount of minerals is not very clear.
Reasonable mineral additions can not only meet the nutritional needs of turtles, but also reduce feed costs. Turtles lack minerals, which not only affect growth and development, but also cause some diseases.
It is generally believed that the appropriate range of calcium content in turtle compound feed is 2.3% to 4.84%, the appropriate range of phosphorus content is 1.2% to 3.0%, and the ratio of phosphorus and calcium should be (1.5 to 2.0):1. The amount of trace elements added to turtle feed can be referred to Table 6-2.