- Water stability (water resistance)
- Crushing granularity of feed raw materials
- Mixing uniformity
- Feed granules' curing degree
(Further reading: MAKE AQUATIC FEED: PELLET FEED OR EXTRUDED PARTICLE FEED?)
Factors affecting fish feed coefficient
1. Rationality of feed formulation
The nutrient content of feed itself has great influence on feed coefficient. Protein and fat content are the two main nutritional indicators of feed, and the higher the content, the lower the feed coefficient, the better the digestion and absorption of fish. However, the diets with the same or similar contents differ greatly from the existing state and structure of their active ingredients. Taking barley, oat and wheat as examples, the protein digestibility of carp to the three kinds of grain feed is "barley > oat > wheat". This is mainly because the protein quality of wheat is worse than that of barley and oat, that is to say, the content of lysine and threonine in wheat is lower. The biological value of protein in feed calculated by essential amino acid index was 55 for wheat, 70 for oat and 73 for barley. In addition, the excessive content of essential nutrients in feed can also cause dyspepsia. For example, when protein content is too high, the accumulation of protein in fish body is almost unchanged, and the weight gain is not proportional to the protein content in feed. This not only causes the waste of protein, but also the metabolites of its protein also pollute the water quality. Therefore, the content of various nutrients in feed should have an optimum amount. Practice has proved that there should be an appropriate proportion between protein and non-protein in fish feed, and only when protein is sufficient, other nutrients can be effectively utilized. If there is a lack of nutrients in feed, it will also affect the utilization of other effective ingredients. Nutrient supplement in feed can increase feed utilization.
The nutritional needs of fish for feed have their own characteristics. For example, fish can make full use of protein and fat in feed, but cannot make good use of carbohydrates, and it is difficult to digest cellulose. Fish have different nutritional needs. Therefore, reasonable feed formulation should be formulated according to different fish. Only when the nutrients in the feed match the needs of fish, can the digestibility and absorptivity be improved and the feed coefficient be reduced. This means that feed coefficient is largely determined by the rationality of feed formulation.
2. Quality and processing of feed ingredients
The nutrient composition of feed materials varies greatly with the variety, origin, grade, foreign body content, storage conditions and storage period. Therefore, feed ingredients have a direct effect on the nutritional composition and quality of formulated feed. The quality of raw materials is good and the grade is high. The compound feed can reach the expected nutritional level. On the contrary, the nutrition of feed will change. In particular, the storage time of feed ingredients has great influence on the nutritional value of feedstuffs. Although the crude protein content of raw materials will not change during storage, the solubility and digestibility of protein will gradually decrease with the prolongation of storage period. When raw materials are stored at 24℃for 2 years, the protein digestibility will decrease by 8%. Other nutrients in raw materials will also have different degrees of efficiency reduction during storage. The loss of VE is the most serious. Fat is decomposed by lipase during storage, and it is easy to deteriorate. The quality of formula feed will be greatly reduced by using this kind of material.
In addition, due to the particularity of aquatic feed, the requirement on its processing technology is relatively high. The main technological indexes affecting the quality of feed processing are particle size, the pressure and temperature of conditioning steam. The results showed that the digestibility of feed processing granularity was 11% in 10-20mesh, 51% in 30-50mesh and 73% in over 50mesh. The fine grain size and large surface area of raw materials can obtain better conditioning effect, has high curing degree, more adequate gelatinization, good cohesion of particles, and is not easy to lose after entering water. Fish are easy to digest and absorb after feeding, and the feed coefficient is low. In the standard of feed processing, the requirement of crushing size of aquatic feed is: fresh water fish feed should pass 20 mesh sieve, 40 mesh on sieve should not exceed 30%; shrimp feed should pass 40 mesh sieve, 60 mesh on sieve should not exceed 20%. Too much feed and too much raw material will increase feed coefficient. In addition, conditioning process is very important to the quality of feed. Steam pressure and the time of material passing through the conditioner determine the degree of material curing. The processing parameters of different raw materials are different. If the water content is insufficient and the temperature is insufficient, the digestibility will be affected by inadequate gelatinization of raw materials, and excessive maturation will destroy the nutrients in feed, of which lysine is the most important one. Thus, the utilization ratio of feed decreased and feed coefficient increased. For aquatic feed, the optimum moisture content of conditioning is about 12%, and the material temperature is 70℃. This can not only improve the production efficiency of the fish feed extruder, but also produce high-quality fish feed products.