What nutritional issues should be noted in mink feeding?

With the rapid development of the mink farming industry, mink feed resources, especially fishery resources, are becoming increasingly scarce, and the proportion of complete compound feed for mink in mink farming is growing larger and larger. To formulate good mink feed, mastering the main nutritional requirements of mink is the prerequisite. A brief introduction to the main nutritional requirements of mink is given here. Energy requirements of mink Currently, there are mainly two feeding standards applied in fur animal production: the NRC fur animal feeding standard, which is the minimum requirement to satisfy normal animal growth, reproduction, production and health, and does not include a safety margin. When formulating the requirements for energy and various nutrients, it takes into account differences in feed chemical composition, genetic differences among breeds, and the effects of climate and housing on requirements. In fur animal nutrition research, gross energy, digestible energy and metabolizable energy have been used to express the energy value of feed, and now ME is mostly used as the indicator to evaluate the effective energy value of feed. The ME value of feed is estimated from the digestible protein, digestible fat and digestible carbohydrates of the feed. NRC and Enggarrd-Hansen adopted the same formula, namely: ME (kJ/g) = 18.8DCP + 39.8DEE + 17.6DCAB. The energy requirement for maintenance (MEM) of fur animals depends on factors such as body weight, activity level and environmental temperature. Studies have found that the energy requirement for maintenance of fur animals is much higher than that of other livestock. The energy requirement for regulating body temperature in fur animals is very important, because fur animals are in environments with a wide range of temperature variation. Yang Jiashi, Jin Shihou and others reported that the fasting heat production and maintenance energy of mink in the early growth stage were 507.9 kJ/kg W0.75·day and 551.0 kJ/W0.75·day respectively; the fasting heat production and metabolizable energy in the late growth stage (fur growth period) were 559.0 kJ/W0.75·day and 579.5 kJ/kg W0.75·d respectively. As for the efficiency of metabolizable energy deposition and utilization in the body, during the growth period Kp was 0.783, Kf was 0.749, and Kpf was 0.766. Yang Jiashi and others recommended the appropriate dietary energy (GE) concentrations for mink during the rearing period, fur growth period, gestation period and lactation period as follows: 20.92 MJ per kg, 20.50 MJ per kg, 20.50 MJ per kg and 20.92 MJ per kg respectively; the dietary metabolizable energy levels in the early rearing period and fur growth period were 16.74 MJ per kg and 16.32 MJ per kg respectively. Protein and amino acid requirements European and American scholars have conducted extensive research on the protein and amino acid requirements of mink, and Glem-Hansen has provided a detailed review of this. The protein requirement of mink is often expressed as the percentage of digestible protein in the dietary ME. Glem-Hansen used the nitrogen deposition method to study the protein requirements of mink at different stages of growth, and found that to achieve maximum nitrogen deposition, the appropriate protein levels at each stage of mink growth were (expressed as DCP as % of ME): 10 to 15 weeks of age, 41%; 16 to 17 weeks of age, 42%; 19 to 21 weeks of age, 32%; 22 to 24 weeks of age, 31%. However, further research confirmed that the appropriate protein level that satisfies maximum nitrogen deposition cannot fully meet the protein requirement for producing the best fur quality. Recent research results from Danish, Norwegian and Finnish scholars show that when 25% of ME in the diet of mink in the late growth stage is provided by DCP, there is no obvious effect on mink fur quality, and 30% of ME provided by DCP can satisfy the needs of mink body weight gain and fur development. However, attention must be paid to the amino acid composition of the diet, especially around 20 weeks of age when fur growth is at its peak, when the sulfur-containing amino acid content should account for 3.5%-4.0% of dietary protein. Skrede studied the effects of different protein resources on protein requirements during the growth period, and the results showed that when poorer protein resources are used, the amount of protein needs to be increased to compensate. When the dietary protein level for adult female foxes is lower than 19%-22%, it is detrimental to fox health and fur quality, while a dietary protein level of 23%-26% before mating is sufficient to maintain body weight for female foxes; during lactation, the dietary protein level for female foxes should not be lower than 25%, otherwise it is detrimental to the growth of fox cubs. In the early growth stage of fox cubs (50 to 160 days of age), a protein level of 28% of dietary dry matter can satisfy normal growth of fox cubs, and in the late growth stage 19%-25% can satisfy the protein requirements for growth and fur development. A notable characteristic of amino acid requirements in fur animals is that the requirement for sulfur-containing amino acids is much higher than that of other livestock. Research has confirmed that the protein contained in mink fur accounts for 7%-12% of total stored protein, of which 60% is cystine. According to Glem-Hansen's research, the minimum dietary sulfur-containing amino acid levels for mink at each stage were (as % of dietary protein): 10 to 13 weeks of age 3.3; 15 to 19 weeks of age 3.1; 20 to 24 weeks of age 4.6-5.1; 26 to 30 weeks of age 3.7-3.8. Research results on the utilization of L-cystine, L-methionine and D-methionine show that D-methionine cannot be used for mink fur growth, while L-cystine and L-methionine can be effectively utilized, and their utilization rates are slightly higher than the sulfur-containing amino acids in feed. There is less research on the requirements for the remaining essential amino acids, and supply standards are mostly estimated based on dietary amino acid content, and most are estimated based on wet feed. Therefore, attention should be paid to the possible damage to feed amino acids, especially cysteine, lysine and arginine, from feed drying and heat treatment. Table 1-2 presents the latest data on the essential amino acid requirements of mink. Due to differences in experimental methods, the results in the table for methionine, cystine, lysine, tryptophan and threonine requirements are relatively accurate. However, because the number of experimental animals was too small, the requirements for the remaining amino acids cannot be precisely determined. From the results of nitrogen metabolism and different nutritional gradient experiments, it is known that the maintenance protein requirements of mink in the early growth stage and fur growth period were 2.13 g/kg W0.75.d and 2.17 g/kg W0.75.day respectively. The protein requirement for growth and development during the growth period can be obtained from the sum of the net protein deposition required for daily weight gain of mink at different weeks of age, the maintenance protein deposition and the maintenance protein requirement, thereby obtaining the protein requirement at the corresponding week-age stages. To determine the balanced amino acid pattern and appropriate ratio in the diet, Jin Shihou and others used the method of body composition analysis of mink at different body weight stages during the growth period, and clarified the proportions of energy substances such as protein, amino acids and fat distributed in the body and the amino acid pattern, so as to obtain the appropriate ratio pattern and requirements of the main essential amino acids in the diet. From this it can also be seen that the maintenance nitrogen requirement accounts for a very small proportion of the total nitrogen requirement (0.35-0.41 g N/kg W0.75.day). Gao Xiuhua and others conducted digestion and metabolism experiments and feeding experiments with growing male mink. In the early growth stage, five diets with protein levels of 26%, 32%, 38%, 44% and 50% were set, and the optimal protein level in the early growth stage was found to be 38%, and 32% in the fur growth period. Su Zhenyu and others set four protein level diets of 34%, 36%, 38% and 40% for mink in the early growth stage, and conducted feeding comparison experiments. The results showed that the optimal protein level was above 36%. Jin Shihou and others designed diets in the early growth stage and fur growth period with tryptophan, valine, threonine, phenylalanine + tyrosine, lysine, methionine + cystine, leucine, isoleucine, histidine and arginine accounting for 1.0%, 4.5%, 4.0%, 6.4%, 6.5%, 3.5%, 7.0%, 4.0%, 2.0% and 5.0% of dietary crude protein content respectively. Feeding experiment results showed that all could ensure normal growth and development of mink and fur growth. Liu Qingren and others once comprehensively expounded the laws of protein nutrition metabolism in mink, as well as the protein requirement, and suggested that the supplemental amounts of Cu, Fe, Zn, Mn, Co and I in mink diets should be 6 mg-8 mg per kg, 5 mg-7 mg per kg, 45 mg per kg, 45 mg per kg, 0.15 mg per kg and 0.9 mg per kg respectively. Fat and fatty acid requirements The fat content in fur animal diets has always been very high. In recent years, digestible fat in Danish mink diets accounts for more than 50% of dietary ME. Therefore, the fat composition of fur animal diets and quality issues related to oxidative stability have become very prominent. Studies have found that when fatty fish is used to replace slaughterhouse offal, the health status and fur quality of mink decline, and excessive marine fish fat can lead to an increased incidence of yellow fat disease, but using good-quality fish and antioxidants can overcome most problems. Yellow fat disease is considered to be the result of the interaction between dietary polyunsaturated fatty acids and their oxidative degradation products and the body's defense mechanisms. Since the 1980s, the use of antioxidants, the addition of vitamin E and the standardization of feed production have significantly reduced the incidence of yellow fat disease. However, during the same period, the incidence of sudden death in fast-growing mink and the related pectoral muscle necrosis increased. Further research found that vitamin E, selenium and polyunsaturated fatty acids are unrelated to sudden death. The negative effects brought by polyunsaturated fatty acids (decreased growth rate, increased bleeding, and pressure-induced red vision) can be avoided by adding vitamin E, but the role of selenium is very small. In the NRC-recommended essential fatty acid requirements for mink and foxes, the minimum level of linoleic acid in the diet of adult mink is 0.5% of dietary dry matter, while the corresponding level for lactation, gestation and growth periods is 1.5%. The minimum essential fatty acid requirement (including oleic acid, linoleic acid and arachidonic acid) for silver foxes is 2 g-3 g per animal per day. The fat content in fur animal diets has always been very high. Dietary fat serves as a source of essential fatty acids (EFA) and fat-soluble vitamins A, D, E and K, and at the same time has the effect of promoting protein accumulation. Only sufficient fat supply can reduce the use of protein for energy consumption and improve the economic benefits of the diet. The energy value of fat and carbohydrates depends on whether the energy they provide is used for tissue synthesis or maintenance of growth. In growing animals, fat energy is more effective than carbohydrate energy for body fat deposition, mainly because fat energy in food can be directly synthesized into body fat. While mastering the main nutritional indicators of mink, when selecting feed ingredients, attention should also be paid to the digestibility and absorption rate of raw materials and processing techniques and methods. Combined with local climate characteristics and feed raw material resources, reasonably set the proportions, pay attention to nutritional matching, formulate a good formula, reduce farming costs, and maximize comprehensive benefits.