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Mink: Recommendect Dietary Allowances ENERGY Maintenance Hodson and Smith (1945) found that mink require 273 kcal of gross energy per kilogram of body weight daily for mainte- nance. More recently, Perel'dik et al. (1972' have listed calculated daily maintenance requirements on a monthly basis, with allowances for variations in environmental temperatures and in body weights. These latter values, rang- ing from 191 kcal ME per animal (nonpregnant female) in April-May to 237 kcal ME per animal in March to 334 kcal ME per animal in October, agree quite closely with practical observations of Rimeslatten in Norway (1964~. Farrell and Wood (1968) reported that female pastel mink used from 202 to 258 kcal of DE (estimated as 182-232 kcal of ME) per kilogram per day for maintenance in the months September to November (in a location of moderate climate). The range resulted from different activity levels attendant upon housing in very small or conventional farm cages. Perel'dik et al. (1972) have summarized daily maintenance re- quirements as 200 kcal of ME per kilogram of body weight throughout the year. More recently, on the basis of regression analysis of the energy gain:energy intake response in growing male mink, Harper et al. (1978) have reported the daily ME requirement for maintenance as 147.8 + 6.06 kcal/kg MBS. From this they have calculated the daily requirement for E as 203 kcal/kg MBS. (In their work, Harper et al. (1978) used BWkg0 73- rather than BWkg0 75 for the calculation of MBS). These authors also recalculated the data of Hodson and Smith (1945), arriving at the value of 260 kcal E/kg MBS/day. Conversion of the value of Harper et al. (1978) to the actual body weight basis yields daily maintenance requirements ranging from 176 kcal ME/kg BW for an animal of 500 g down to 124 kcal ME/kg BW for an animal weighing 2,000 g. Chwalibog et al. (1979) also used regression analysis of the results of energy balance experiments to estimate the main- tenance requirements of adult male mink; they found a marked effect of environmental temperature and of dietary protein level on the retention of energy by the animals. In the thermoneutral zone (20°C), the maintenance requirement was found to be 126 keel ME/kg MBS. (In addition to using MBS as a basis, these workers expressed energy as kilojoules; conversions to kilocalories have been made for the present discussion.) For comparison with the values of Harper et al. (1978), this maintenance requirement corresponds to values for mink ranging from 500 to 2,000 g BW of 150 to 106 kcal ME/k~ BW. The lower values of Chwalibog et al. may be related to the strict temperature control in their experiments or to the use of older animals or to both. Glem-Hansen and Chwalibog (1980) found that the requirement for ME in- creased by 3.7 kcal/MBS per degree Celsius per day. In the light of the diverse experimental methods and cir- cumstances involved in the various studies described above and the ranges of results reported, the establishment of a firm recommendation for maintenance energy requirements is im- possible. However, giving extra weight to the results of the more recent careful studies, a daily intake of 140 kcal ME/kg BW for the maintenance of mature mink is suggested as a ten- tative guideline. Limited experimental data are available on the requirements of energy by mink during pregnancy, largely as a consequence of the obvious difficulties of conducting and assessing such studies. One common suggestion, on the basis of limited North American studies (Travis and Schaible, 1961; Evans, 1964a), has been that adequate performance will be achieved by pro- viding diets of energy content comparable to that of diets used for optimal early growth of kits. Recommendations on a more fundamental basis have been made by European investiga- tors. Perel'dik et al. (1972), after reviewing Scandinavian pro- duction records and recommendations, as well as the recom- mendations for other forbearing species, suggested that the needs of the pregnant female mink will be met by increasing the maintenance energy allowance by 15 percent during the last month of pregnancy. Thus, a level of 230 kcal of ME per kilogram of body weight per day was recommended by these authors. This level, being based on maintenance recommen- dations of Perel'dik et al. (1972), which are much higher than 7
8 Nutrient Requirements of Mink and Foxes those proposed in the preceding section, appears rather high. In the absence of any more fundamentally derived estimates, however, there is no justification for proposing an intake of less than 200 kcal ME per kilogram of body weight during the last month of pregnancy. Lactation and Growth The growth of kits during the first 3 weeks of life depends upon energy supplied by the dam's milk, and, to a declining extent, this demand continues until weaning. Consequently, the lac- tating female must receive additional energy for milk produc- tion, the amount required increasing with the increasing demands of the developing kits for energy and nutrients. Based on calculations from production data on Russian and Scandinavian farms, Pereltdik et al. (1972) have presented recommendations for increased energy supplies to lactating females on the basis of the following scale of daily levels of ME per kit during successive 10-day periods of the lactation: 5, 20, 50, 70-90, and 110-150 kcal. Multiple regression studies in Denmark (N. Glem-lIansen, National Institute of Animal Science, Hilleroed, Denmark, personal communication, 1978) have provided information on the additional re- quirements of the lactating female for ME, above the maintenance requirement, to provide for weight increase in her kits. A mean value of 2.6 kcal ME per gram of kit weight increase was derived. Although this mean value can serve as a guide, it should not be applied indiscriminately. In practice, the increments required will be achieved by increased con- sumption of the high-energy diet by the female. The weaned kit must obtain its entire energy supply from the growth diet; the requirements will increase rapidly with the rapid growth, especially during the early weeks. The kit will be able to meet these requirements by increasing the con- sumption of the diet, provided the energy content of the diet is high enough. Because of the rapidly changing kit weights, re- quirements are more commonly expressed as averages per day rather than on the weight basis (per kilogram). Rimeslatten (1964) and, later, Perel'dik et al. (1972), working from data from numerous Scandinavian and Russian practical studies, calculated average combined figures for male and female kits for each month of the growing period. These figures also in- cluded an increase of 10 percent to cover practical en- vironmental conditions and were as follows: Early Period Late June July August ME kcal/day 200 250 310 * Includes furring as well as growth. Late Period* September October November December ME kcal/day 340 330 300 280 These authors noted that the male required 33 percent more energy than the female. These different requirements will usually be met by differential intakes of a single diet of ade- quate energy concentration. Practical recommendations for energy supplies for growing mink have most commonly been made in terms of energy per kilogram (or per 100 g or per gram) of diet. Allen et al. (1964) reported that a minimum of 4.9 kcal of E or 3.7 kcal of apparent DE per gram of feed dry matter (DM) would be required for optimal early growth of male mink kits and that 4.5 kcal of E per gram DM (3.4 kcal DE) would suf- fice for female kits. Later recommendations from the same laboratory, based on further studies with larger genetic strains (Evans, 1964a; Evans and Travis, 1967), repeated and con- firmed over several years using different dietary ingredients and at different locations, were 5.3 kcal E per gram DM of diet for males and 5.1 kcal E per gram DM of diet for females. This recommendation for males was supported by Wood and Farrell (1965~. Using the previously cited average figure of 77 percent for converting E to ME values, the above E recommendations of 5,300 and 5,100 kcal become, respectively, 4,080 and 3,930 kcal ME per kilogram DM of diet, values adopted for use here. Energy Density and Its Implications The concept of energy density of diets is of both theoretical and practical importance. It deals with the concentration of energy in the diet. A diet of high-energy density (often referred to simply as a "high-energy diet") provides more kilocalories per gram than does a diet of low-energy density ("low-energy dieted. In the recommendations cited in the preceding section, the diet of 4,080 kcal ME per kilogram is of greater energy density than the one of 3,930 kcal ME per kilogram. Diets used experimentally and practically, however, have ranged from much higher to much lower energy densities than these. For example, records from 45 Danish central feed-processing units during 1969 and 1970 showed variations in energy density from 3,400 to 3,900 kcal ME per kilogram of DM (Nielsen, 1973~. Similarly, Swedish practical mink diets have ranged from 3,500 to 4,SOO kcal ME per kilogram of dry matter iE. Alden, Department of Animal Husbandry, Agricultural Col- lege of Sweden, personal communication, 1978~. It is of interests that some Scandinavian investigators are convinced that the optimal energy densities of diets vary depending upon the DM contents of the diets as fed, as well as upon the nature of the diet ingredients. For instance, success with the feeding of dry diet forms is believed to be contingent upon a relatively high energy density in the diets (G. Joergen- sen, National Institute of Animal Science, Hilleroed, Den- mark, personal communication, 1978~. Since the mink generally eats to satisfy energy demands and will curtail intake when these demands are met, the density of energy in a diet will be a main factor governing feed intake, assuming that palatability is ensured. Thus, an animal will re- quire and will consume less of a high-energy density all-et and more of one of low-energy density. It has been noted that feed consumption varies inversely with energy density over a con- siderable range of density values (Evans, 1963~. Calculations of energy density of diets in over experiments, in which published variable feed intakes were either not accounted for or not commented on, strongly suggest that the energy den- sities were probably important causative factors of the dif- ferential intakes.
Nutrient Requirements of Mink and Foxes 9 This relationship between energy density and consumption of diets is the major argument in favor of the principle of ex- pressing nutrient recommendations on a basis that relates them to the energy recommendations. It should be emphasized that factors such as palatability and digestibility of the feed and the feeding technique (i.e., ad libitum or restricted feeding) will have marked effects on the level of feed consumption. The capacity and the digestive capability of the gastrointes- tinal tract of the mink are limited, and it may be physically impossible for an animal to consume sufficient amounts of a low-energy diet to satisfy energy demands; this will be par- ticularly true in periods of high-energy requirements such as lactation and early kit growth. It is also important that the diets fed during these periods be of high palatability and digestibility. Conversely, too great a concentration of energy in the diet may have adverse effects, primarily by reducing total diet intake and perhaps causing deficiencies of protein or other essential nutrients. A considerable margin exists, however, in both directions. Within these limits, the decision as to whether the energy density of the diet will be selected to coincide with the density required to produce optimal growth or at levels above or below this optimum may well depend upon the relative costs of feed ingredients. FAT Fat (lipid), as the most concentrated supplier of energy to diets, is the (actor that plays the greatest role in varying the energy density of those diets. Consequently, high-energy diets are, of necessity, diets that are relatively high in fat. The fat may be supplied to varying degrees as a constituent of com- monly used feed ingredients. Thus, most animal and fish prod- ucts and by-products are substantial, but variable, con- tributors to the fat content of the diet. On the other hand, many of the ingredients of cereal or other products of plant origin are usually low in fat. In many instances the addition of rendered fats or oils (tallow, lard, fish oils, vegetable oils, etc.) will be necessary to achieve desired energy levels in the diets; the need for and the extent of this supplementation will de- pend upon both the other diet components and the life-stage of the animals to receive the diet. The need for adding fat to certain diets was reported by Belcher et al. (1958) for growing mink and by Friend and Crampton (1961a) for reproduction. The inclusion of certain high-fat ingredients (particularly certain fish products) or the addition of fat supplements to mink diets was, for many years, considered undesirable based on reports of untoward effects; stimulation of yellow fat dis- ease or the causation of wet-belly disease were two major criti- cisms of these ingredients. There is clear evidence that yellow fat resulted from the poor quality, i.e., the rancidity, of the fat in the ingredients. Care in the selection of these ingredients and the correct use of antioxidants in the storage of ingredients and in preparation of the mixed diets can eliminate this prob- lem. The case concerning wet-belly is less clear, and contra- dictory reports have appeared, some suggesting possible asso- ciation of wet-belly with high fat levels (Leoschke, 1959a; Evans et al., 1961) and others reporting little or no problem with certain strains of animals receiving high levels of fat in the diet (Stout et al., 1964, 1965; Evans, 1964b, 1967a). Another problem once attributed to high fat intakes was poor color in dark pelts (Stout et al., 1963~; however, later reports (Stout et al., 1965) covering 1,500 mink indicated no direct causal relationship between diet fat level and fur color. There is general agreement that the percent digestibility of most fats is quite high (with the exception of certain very hard tallows) and that the separated fats may frequently be di- gested to a higher degree than those associated with certain of- fals and other ingredients (Leoschke, l959b; Lehman, 1959; Evans, 1967b; N. Glem-Hansen, National Institute of Animal Science, Hilleroed, Denmark, personal communication, 1978~. The digestibilities of the fat of most mixed diets will range be- tween 80 and 90 percent (rarely higher) with a mean of 85 percent or more. Comprehensive Danish investigation Uoer- gensen and Glem-Hansen, 1973) showed that 85 percent of the variation in the digestibility of fats by mink is due to the con- tent of stearic acid (the saturated 18-carbon fatty acid). These workers presented a formula by which the digestibility of a fat can be calculated if the content of stearic acid is known. The levels of fat reported to have been used satisfactorily in mink diets range up to 35 or 40 percent of DM. The total dietary fat required to achieve, for example, an E content of 5.3 kcal of E per gram of DM of diet will usually be approx- imately 25 percent of the DM, the level required for optimal metabolic performance and utilization, depending, of course, on the digestibility of the particular fat. Perel'dik et al. (1972) and Leoschke (1980) have made recommendations on two bases-as grams of digestible fat per day per kilogram body weight or as percent of the total ME. Leoschke's recommendations on the latter basis are for fat to supply the following percentages of the total ME of the diet: for growth 44-53 percent, for fur development (including late growth) 42-47 percent, for pregnancy 34-37 percent, and for lactation 47-50 percent. In addition to its contributions of energy, dietary fat must also provide the required amounts of essential fatty acids, notably linoleic acid. Unfortunately, only limited data on these requirements are available. From a review of published reports Perel'dik et al. (1972) concluded that the minimum supply of essential fatty acids necessary to maintain healthy adult animals was 0.5 percent of the diet DM; for pregnant and lactating females and young growing mink 1.5 percent of the diet DM was recommended. (If one assumes a typical diet providing 4,000 kcal ME/kg DM, this latter recommendation involves 60 kcal ME, or 1.5 percent of total ME, from linoleic acid.j More recently, N. Glem-Hansen (National Institute of Animal Science, Hilleroed, Denmark, personal communica- tion, 1978), in investigations of the requirement of the lac- tating female as judged by growth of the nursing kits, found a higher requirement of linoleic acid 5 percent of the ME in the diet-for optimal kit growth from birth to weaning. CARBOHYDRATE S No critical studies have been made on the carbohydrate re- quirements of mink; indeed, there have been no indications
10 Nutrient Requirements of Mink and Foxes that there is an actual requirement. The primary (and perhaps the sole) function of carbohydrates in mink diets is, as in diets of other species, to supply energy; there are no reports of other special functions for any particular forms of carbohydrate. Widely different levels of carbohydrates have been used in mink diets, the higher levels usually occurring in experimental diets. For example, Tove et al. (1949) fed a purified diet con- taining 60 percent sucrose. In most practical diets and in many experimental diets the carbohydrate content often exists largely as a filler to provide the remainder of the energy after certain specific protein and fat levels have been selected. Thus, the levels of carbohydrate in such diets vary inversely with the levels of protein and energy. Recommendations for satisfactory levels in diets for various life stages reflect this fact. Pereltdik et al. (1972), citing the Scandinavian work of Rimeslitten (19S9a), Nhman (1961), and loergensen (1967), recommended that carbohydrates supply not less than 10 per- cent and not more than 30 percent of ME; the best results will be obtained, it was suggested, when 15 to 25 percent of the ME is supplied by carbohydrates. Leoschke's recommenda- tions (1980) cover the same general span, but they specify the following ranges, as percent of ME: for growth and for fur development, 15-30; for pregnancy and lactation, 10-20. Starch is the major carbohydrate of ingredients used in mink diets; in most of these sources the digestibility (and hence the ME contribution) of the starch can be significantly in- creased by cooking, "popping," or similar heat treatment o (Ahman, 1959; Evans, 1964c; Leoschke, 1965; Glem-Hansen and Joergensen, 1978~. Glem-Hansen et al. (1977), working in Denmark, have shown that a reasonably accurate estimate of the digestibility of a carbohydrate by mink can be made by a calculation based on the results of analyses of the content of or-linked glucose in the feed sample before and after auto- claving. PRO TE IN Animals do not require protein of itself, but actually require the individual amino acids present in the feedstuff protein. It follows, then, that the designation of specific protein re- quirements for the mink is difficult. The animal's protein re- quirement will be related to the protein quality in a given feedstuff. Amino acid balance and amino acid availability are the two primary factors providing the bases for defining a protein feedstuff as high or low quality. Meat is illustrative of a high- quality protein feedstuff, as it possesses a protein content that (1) is highly digestible by animals and (2) contains an amino acid pattern similar to the actual amino acid requirements of the animal. Chicken feet are illustrative of a low-quality pro- tein feedstuff, because (1) the protein is relatively indigestible (only 52 percent digestibility rating for mink ~Leoschke, 1959b]) and (2) the amino acid balance is inconsistent with the actual amino acid needs of the mink as a consequence of relatively low levels of certain amino acids such as tryp- tophan. Carefully processed fish meal products have good digestibil ity ratings for mink and a good amino acid pattern. However, overheated fish meal products are unable to provide the mink with a pattern of digestible amino acids consistent with the ac- tual needs of the animal. Excessive heating of fish products in the dehydration procedures can result in the destruction of the amino acid lysine and the bonding of the amino acid arginine in an indigestible form (Allison, 1949~. Tryptophan and the sulfur amino acids, cystine and methionine, are especially sen- sitive to destruction during the dehydration of protein foodstuffs (Varnish and Carpenter, 1975~. The protein quality of a feedstuff is related to the amino acid pattern and availability of the amino acids present in the proteins to the digestive process of the animal. It is apparent that protein quality is of major importance in the assessment of the protein requirements of the mink inasmuch as the mink have (1) a limited digestive capability due to a relatively short time of feed passage (average passage time 142 minutes) (Sib- bald et al., 1962) and (2) an extra requirement for arginine and the sulfur amino acids during the critical fur-development months (Leoschke and Elvehjem, 1959a; Glem-Hansen, 1980a,b,c). Protein quality and dietary energy density account, in part, for the great variation in experimental data on the protein re- quirements of the mink. Feed intake of the mink is primarily determined by the taste appeal and caloric density of the diet. Considering the critical role of dietary energy densi.ty in the determination of mink feed intake, it is logical to relate the protein requirements of the mink to the energy content of the diet rather than to list them simply as a percentage of protein in the diet. Lower levels of protein than those indicated in Table 1 may yield quite satisfactory performance if the protein quality is superior and the fat:carbohydrate ratio is kept high. This has been shown repeatedly when feeding complete dry diets. On the other hand, when the diet contains largely poor-quality sources of protein, it may be advisable to increase the mini- mum recommendation with a safety margin. It is important to emphasize the fact that the data presented in the tables represent the minimum protein requirement of mink during different phases of the life cycle. Producers may wish to use higher protein levels to provide a margin of safety. Producers are advised to be aware of problems likely to be associated with borderline protein nutrition, including re- tarded growth, suboptimal fur development, and poor repro- duction-lactation performance of the mink. Gestation Experimental data from mink fed diets that contained 40, 45, and 50 percent digestible protein indicated no significant dif- ference in reproductive performance (Petersen, 1957a). Nor- wegian studies cited by Glem-Hansen (1974) have shown that diets varying from 29 to 64 percent of the ME from digestible protein (for calculations see Table 9) did not significantly in- fluence the reproductive performance of the mink. Studies covering a slightly wider range of protein content (Glem- Hansen, 1974) have shown a tendency toward suboptimal re- productive performance with dietary protein levels both very high (70 percent of ME from digestible protein) and very low
Nutrient Requirements of Mink and Foxes 11 (25 percent of ME from digestible protein). Results of the Scandinavian investigations indicate a minimum protein re- quirement of 35 percent of the ME from digestible protein during the critical gestation period. Lactation Investigations by Lehman (1967) and Joergensen and Glem- Hansen (1970, 1972) have shown that calories from digestible protein during lactation should be higher than 40 percent of the total ME in the diet. Glem-Hansen (1979) studied the lac- tation performance of females and early growth of mink kits in the period from birth to 42 days of age. Prior to whelping, all experimental females received the identical farm feed. The in- vestigation involved protein levels ranging from 21 to 54 per- cent of the ME from protein. The growth performance of the mink kits receiving 42 percent ME from digestible protein was superior to that of kits on the 34 percent level and lower levels of protein. Early Growth /~9-13 Weeks) The protein requirement of mink during the growth period from about 9 to 28 weeks of age has been studied by a number of investigators including Sinclair et al. (1962), Allen et al. (1964), Adair et al. (1966), Joergensen and Glem-Hansen (1970, 1972), and Skrede (1975, 1978~. These experiments in- dicate that the protein requirement for this period is about 35-45 percent of ME from digestible protein depending on quality. Experiments in which the growth season was divided into periods showed that the protein requirement from birth to 16 weeks of age is higher than during the period from 16 to 28 weeks of age Uoergensen and Glem-Hansen, 1970, 1972~. Studies by Glem-Hansen (1980a' indicate that the digestible protein requirement during the period of early growth from 9 to 13 weeks of age is approximately 35-40 percent of the ME. It is important to note that the protein recommendations made in the preceding paragraphs apply to male kits. A num- ber of studies indicate that the actual protein requirement for female kits will be considerably lower. In studies conducted by Glem-Hansen (1980b), a level of 42 percent ME from digestible protein was required for optimal growth of male kits during the period from birth to 42 days of age. However, these same investigations indicate that a level of 34 percent ME from digestible protein will provide optimal weight gains for female kits during the period from birth to 6 weeks. Growth studies by Leoschke (Valparaiso University, personal communication, 1978) with mink kits 7 to 10 weeks old in- dicated significantly lower protein requirements for female kits relative to male kits. Late Growth (13-30 WeeksJ Howell and Gunn (19SS) considered 32 percent crude protein to be sufficient for maximum growth of mink, while Stout et al. (1963) found that a level of 25 percent crude protein during the growth period was necessary for maximum growth of body and fur. The protein requirement of mink during the late growth period has been studied by a number of other investi gators including Sinclair et al. (1962), Allen et al. (1964), Adair et al. (1966), Joergensen and Glem-Hansen (197O, 1972), Skrede (1975, 1978), and Glem-Hansen (1980b). These studies indicate that the digestible protein requirement for the late growth period is approximately 30 percent of the ME. Fur Development (16-30 Weeks) Studies by Glem-Hansen (1980b) indicate that, although a protein level of 24 percent of ME from digestible protein is satisfactory for maximum growth of the mink in the period from 16 to 30 weeks, this protein level does not necessarily en- sure maximal fur development. Glem-Hansen recommends a diet containing 30-35 percent of ME from digestible protein during the critical fur development phase. Amino Acid Supplementation A number of studies have been conducted on the value of sup- plementing practical ranch diets with specific amino acids. Some of the earliest studies on amino acid supplementation of mink diets were conducted at Oregon State University (Watt, 1952~. These studies indicated that supplementation of high- fish diets with 0.05 percent methionine (dry basis) improved the growth and fur quality of the mink. Studies at the Univer- sity of Utrecht by Hoogerbrugge (1968) showed the value of lysine and methionine supplementation of dry diet formula- tions. Dehydration procedures required for the production of fish meals and poultry by-product meals may result in lysine destruction, hence the benefits of lysine supplementation for dry diet and pellet formulations. Heat Processing of Protein Feedstuffs Heat processing of mink feedstuffs may increase or decrease the nutritional value of these products for mink. Cooking of eggs is an absolute requirement for their use in practical mink rations. lIeating of eggs for at least 5 minutes at 91°C (196°F) denatures avidin, a protein that binds the vitamin biotin in an indigestible linkage. Heating of eggs also denatures egg pro- teins that bind iron in a structure unavailable to the digestive processes of the mink (W. L. Leoschke, Valparaiso University, personal communication, 1978~. Heat processing of raw soy- bean oil meal is essential for the denaturation of a trypsin in- hibitor (trypsin is a protein-digesting enzyme). Conversely, heat processing of mink feedstuffs such as fish and poultry by- products (heads, entrails, and feet) may actually lower their nutritional value. Studies have shown that certain amino acids including lysine and arginine are heat-labile (Allison, 1949~. It is important to note that arginine is of critical importance for the fur development of the mink (Leoschke and Elvehjem, 1959a). FAT-SOLUBLE VITAMINS Vitamin A (Retinol) A growing mink needs between 100 and 400 international units (IU) of vitamin A per kilogram of body weight daily (1
12 Nutrient Requirements of Mink and Foxes IU = 0.3 ,ug retinal). At the 100-IU level, the amount stored in the liver is slight; at the 400-IU level, the amount stored is sig- nificantly larger (Abernathy, 1960~. The amount suggested to meet the requirement is about 200 IU per kilogram of body weight. Because a rapidly growing mink kit needs between 275 and 350 kcal of ME per kilogram of body weight per day, a requirement of 200 IU per kilogram of body weight will be met by a diet providing 57 to 72 IU of vitamin A per 100 kcal of ME. Experiments conducted by Warner et al. (1963), in which plasma and liver vitamin A levels were measured after feeding carotene or alfalfa meal, showed that mink are inefficient in converting carotene to vitamin A. This work demonstrates that alfalfa meal and probably other plant sources of carotene are poorly utilized by mink. In the absence of evidence to the contrary, the carotene content of the diet should be disre- garded in supplying the vitamin A requirement for mink. Signs of Deficiency Vitamin A deficiency has been produced and described for mink (Helgebostad, 1955; Stowe et al., 1959; Abernathy, 1960~. When a purified diet devoid of vita- min A is fed, animals fail to grow normally. They develop night blindness and lack coordination, particularly in the rear quarters. Their eyes are affected, with the lenses becoming opaque and the conjunctival encrusted. Metaplasia of epithe- lial tissues and fatty infiltration of the liver occur. The skull does not enlarge normally; as a result, the cerebellum is com- pressed and herniates into the foremen magnum. Damage to the cerebellum results in muscular incoordination. Signs of Excess Helgebostad (1955) investigated effects of high levels of vitamin A on kits and adults. Mink tolerated 40 IU of vitamin A per gram of body weight without disturbance over periods of 3 to 4 months. Fully grown animals could tolerate from 200 to 300 IU per gram of body weight daily for from 6 to 8 weeks, but young animals were affected in a shorter time. Signs of excess were anorexia, bone change with exostosis, decalcification and spontaneous fractures, losses of fur, exophthalmia, and hyperesthesia of the skin. Adair et al. (1977) and Travis (1977) conducted a coopera- tive study in which levels of 1,000 to 160,000 IU of vitamin A per mink per day (approximately 1-160 IU per gram of body weight per day) were fed during the reproductive cycle start- ing in January. Reproduction was normal (4.7-4.9 kits per female on experiment) in the mink receiving from 1,000 to 10,000 IU per mink per day, slightly reduced (3.6-3.7 kits per female on experiment) in the mink receiving from 20,000 to 40,000, and severely reduced (0.86 kits per female on experi- mentJ in the mink receiving 160,000 IU of vitamin A per mink per day. Reduction in performance in the latter group was due to failure of females to whelp, to smaller litter size, and poorer kit survival. Friend and Crampton (1961b) observed that reproductive performance in mink was reduced when whale liver in breeder diets was increased from 5 to 10 percent. They postu- lated a hypervitaminosis A toxicity. Assuming that these mink consumed 15 g per day of whale liver, containing 4,400 IU of vitamin A per gram, they would have received 66,000 IU of vitamin A per day from the whale liver alone. Vitamin D Bassett et al. (1951) suggested that a diet of natural foodstuffs without a vitamin D supplement is probably adequate for v v . A A daily supplement of 200 IU of vitamin D per kg of body weight does not prevent ra- chitic changes when calcium or phosphorus is deficient nor does it improve physiological responses on adequate mineral levels. Danish experiments with 10, 25, and 40 IU vitamin D per gram of dry matter per day from July to pelting did not show any significant differences in pelt characteristics (Hille- man, 1978~. growing mink exposed to sunlight. Signs of Deficiency Mink, when they are fed a diet that is low in vitamin D with an abnormally low calcium-to-phos- phorus ratio, develop rickets (Smith and Barnes, 1941; Bassett et al., 1951~. Also, when the diet is deficient in calcium or phosphorus, bone development is abnormal. Signs of Excess Large doses of vitamin D over a period of time can produce a toxic effect, particularly when the diets are high in calcium. The clinical signs are loss of appetite, nausea, loss of weight, and digestive disorders. Hypervitaminosis can take place in 2 or 3 weeks when the daily dose in the food is 10,000 IU or more per kilogram of body weight (Pereltdik et al., 1972~. Vitamin E Vitamin E is defined in terms of the activity of one of its forms (1 IU of vitamin E = the vitamin E activity of 1 mg of syn- thetic, racemic o`-tocopheryl acetate). Vitamin E acts both as a vitamin and as an antioxidant Vitamin E is spared by other antioxidants in the feed or added to the feed. Conversely pro- oxidants such as iron or copper cause its destruction. Thus, the requirements for vitamin E cannot be stated without consider- ation of the specific conditions of the diet fed. Requirements of o`-tocopherol were determined by Stowe and Whitehair (1963) to be about 25 mg per kilogram of a purified diet with molecularly distilled lard as a source of fat. This is equivalent to 0.66 mg per 100 kcal of ME. The exact interrelationship between vitamin E and the min- eral selenium is unknown and may vary between species. A level of 0.1 ppm of selenium as sodium selenite added to a vita- min E-deficient diet of mink prevented all lesions except minor accumulations of amorphous nonacidfast material at the adipose interstices (Stowe and Whitehair, 1963~. Mink fed marine products are generally supplied adequate levels of sele- nium in the diet (Kangas, 1974~. When mink diets contain rancid fats or are high in polyun- saturated fatty acids (PUFA), the animals are subject to yellow fat disease. * Mink receiving such diets require an ade- quate supply of vitamin E, especially during growth (Lalor et al., 1951; Mason and Hartsough, 1951; Ender and Helge *This disease has been given various names, including yellow fat dis- ease (McDermid and Ott, 1947), nonsuppurative panniculitis (Quor- trup et al., 1948), Weber Christian disease (Quortrup et al., 1948), and steatitis (Hartsough and Gorham, 1949~.
Nutrient Requirements of Mink and Foxes 13 bostad, 1975~. The best information available is that of Harris and Embree (1963), who proposed a dietary a-tocopherol: PUFA ratio of 0.6 (milligrams:grams) for humans as a mini- mum to protect against PUFA oxidation. For information on the effects of antioxidants on the incidence of yellow fat disease, the reader is referred to the section on antioxidants. Signs of Deficiency Signs of an uncomplicated deficiency produced using a purified diet include sudden death due to minor stress, dystrophic lesions of the intercostal and myocar- dial muscles, and hepatic fatty infiltration (Stowe and White- hair, 1963~. The most significant clinical sign was increased erythrocyte fragility (Stowe and Whitehair, 1963~. Similar le- sions have been reported in mink on practical ranch diets by Nordstoga (1969~. Kits with yellow fat disease are first affected shortly after weaning, and losses may continue until pelting time. The dis- ease usually appears suddenly. The kits may refuse the night feeding and be dead in the morning. Other affected kits may leave their feed and show a peculiar, unsteady hop. The im- paired gait may become gradually worse until the animals are unable to move. They become comatose and remain so until they die. In a typical outbreak, without early treatment, nu- merous losses may occur. Vitamin E supplementation is usu- ally effective. At pelting time, nearly all the kits that survive on vitamin E-deficient diets show yellow discoloration of the fat. Blood appears in their urine. An examination of the blood suggests that a general normocytic, normochromic anemia, which does not respond to administration of iron, is a further sign of yellow fat disease (Gorham, 1963~. "Cotton fur" may accompany this condition if rancid fat is fed during the period of active fur formation (Stout et al., 1960a) (Figures 6 and 7~. Also, the frequency of "red hips" (poor-quality fur or unprime areas on hips) increases (G. Joer- gensen, National Institute of Animal Science, Hilleroed, Den- mark, personal communication, 1978~. Vitamin K Little work has been done on vitamin K levels in mink diets, and a deficiency of vitamin K in practical diets appears un- likely. Travis et al. (1961) found that adding vitamin K to a basal semipurified diet low in the vitamin (0.037 ,ug per 100 kcal ME) produced no change in blood prothrombin time. WATER-SOLUBLE VITAMINS Ascorbic Acid (Vitamin CJ No requirement for vitamin C for growth or reproduction has been demonstrated on diets adequate in other nutrients (Bas- sett et al., 1948; Petersen, 1957b). Biotin Biotin deficiencies have been produced by feeding purified diets to growing kits (Travis et al., 1968~. The requirement was shown to be less than 0.003 mg per 100 kcal ME (Schimel- man et al., 1969~. This was the lowest experimental level in- vestigated. Deficiencies of biotin are not normally en- countered on conventional mink diets. However, they can be induced by inclusion of turkey breeder offal or eggs in the diet because of the presence of avidin (Stout et al., 1966; Wehr et al., 1980~. Avidin is a protein found in egg white and oviduct tissue, which binds biotin preventing its absorption (Fraps et al., 1943~. Stout et al. (1966) demonstrated that biotin deficiency resulted from feeding practical mink diets composed of high levels (40 percent or more of diet dry matter) of offal from breeder hen turkeys. Presence of raw eggs in the offal was pre- sumed responsible for the deficiency. The deficiency can be prevented by feeding the offal at subcausative levels, by heat- ing it to denature the avidin (91°C t196°F] for 5 minutes) (Stout and Adair, 1970a), or by supplementing the diet with synthetic biotin. Conventional mink diets do not appear suffi- ciently rich in biotin to counteract avidin. Signs of Deficiency The biotin deficiency that results from feeding the offal from laying hen turkeys causes gray or banded underfur in dark mink (see Figure 5) and, in extreme cases, hair loss. When fed biotin-free purified diets, the defi- cient animals showed "spectacle eyes," crusty feet, yellow or bloody exudate, and a dermatitis of the foot pads in addition to the gray underfur (Travis et al., 1968~. Biotin deficiency has been experimentally produced in mink by feeding raw egg white as 30 percent of the dietary protein (Helgebostad et al., 1959~. Signs noted were pronounced achromotrichia, reduced fur quality, hair loss, degenerative changes in the hair follicles, thickened and scaling skin, con- junctivitis, fatty infiltration of the liver, and ultimately death. There are wide differences in the effects of feeding similar levels of chicken and turkey eggs to mink. From results of mink feeding trials, it appears that turkey eggs contain three to four times as much avidin as do chicken eggs (Stout and Adair, 1969~. Inclusion of as little as 5 percent of spray-dried chicken eggs in mink diets unsupplemented with biotin may also cause fur graying (Wehr et al., 1980) and total reproductive failure (Aulerich et al., 1981~. Folic Acid Based on observations of Schaefer et al. (1946), a level of 0.5 mg per kilogram of dry feed, or 0.135 mg per 100 kcal ME, has been suggested as an adequate level of intake. Given at this level, folic acid caused remission of deficiency signs (growth stunting, diarrhea, and loss of appetite); however, levels below this were not fed. This level is lower than that found in typical diets fed to ranch mink. Niacin The mink requires niacin in the diet, because it is unable to convert sufficient tryptophan to meet its niacin requirement. Mink gained weight when fed a purified diet supplemented with 0.5 mg of niacin per 100 kcal ME, but lost weight and died when supplemented with 0.25 mg of niacin per 100 kcal
14 Nutrient Requirements of Mink and Foxes ME (Warner et al., 1968~. It is unlikely that supplementation of typical mink diets is required, since they have been shown to contain 50 to 75 mg per kilogram of diet, or approximately 1.25 to 1.87 mg of niacin per 100 kcal ME (Rimeslatten, 1966a; Utne, 1974~. Mink milk is unusually high in niacin. Joergensen (1960) found 16 mg of niacin in 100 g of mink milk, which is about 20 times the concentration found in cow's milk and twice that found in the milk of the sow. Signs of Deficiency Young mink fed on a niacin-deficient diet by Warner et al. (1968) displayed rather nonspecific symptoms, including loss of appetite, loss of weight, weak voice, general weakness, and a bloody stool. More than 50 percent died within 6 days after being placed on the niacin- deficient diet. Pantothenic Acid Studies by McCarthy et al. (1966) placed the requirement for pantothenic acid at 0.20 mg per 100 kcal ME. Signs of Deficiency Early signs of deficiency were loss of ap- petite and reduced serum cholesterol levels. Blood appeared in the feces 8 or 9 days prior to death and continued to death. Clinical findings were diarrhea, weakness, emaciation, and dehydration. vitamin B6 Vitamin B6 exists in three interconvertible forms: pyridoxine, pyridoxal, and pyridoxamine. Of these, pyridoxine is the most commonly used as a supplement in animal diets. The vitamin B6 requirement for growth and normal metabolism, using purified diets, was 1.6 mg per kilogram of feed, or 40 ,~g per 100 kcal ME (Bowman et al., 1968~. For reproduction, studies by Rimeslatten and Aam (1962) indicated that the requirements were not met by 3.2 ma, but that they could be met with 9.5 mg of pyridoxine per kilogram FIGURE 5 Marginal biotin defi- ciency in dark mink. Pelts are parted to show underfur. Left to right: Nor- mal, gray, and gray-banded underfur. SOURCE: F. M. Stout, Oregon State University, Corvallis. of dry feed (approximately 80 and 237 ,ug per 100 kcal ME). Joergensen et al. (1975) found increasing blood levels of vitamin B6 with feed levels up to 14 mg per kilogram of dry matter, while 30 mg of the vitamin per kilogram gave the same blood levels as 14 ma. Studies by Akimova, cited in Feeding Fur Bearing Animals (Perel'dik et al., 1972), in- dicated that a vitamin B6 deficiency during growth influenced the breeding results of the following reproduction period. Signs of Deficiency Signs of deficiency in growing kits ap- peared after about 2 weeks on a purified vitamin B6-deficient diet and included reduced feed intake, loss of weight, diar- rhea, brown exudate around the nose, excessive lacrimation, swelling and puffiness around the nose and face region, apathy, muscular incoordination, convulsions, and finally death unless relieved by supplementation with vitamin B6 (Bowman et al., 1968). A deficiency of vitamin B6 during the reproductive cycle reduced the number of females conceiving and lowered the number of kits per litter (RimeslAtten and Aam, 1962~. Mink fed desoxypyridoxine, an antagonist of pyridoxine, did not re- produce due to resorption of the embryos by females. There was also a degeneration of the testes in males (Helgebostad et al., 1963~. Riboflavin Based on studies using purified diets, Leoschke (1960) deter- mined riboflavin requirements for growing kits to be about 1.5 mg per kilogram of dry feed, or 40 ,ug per 100 kcal ME. Short-term trials with fully grown mink Joergensen et al., 1975) showed unchanged levels in blood, muscles, and organs with levels of from 4.5 to 26 mg riboflavin per kilogram dry matter of feed. Signs of Deficiency Mink fed purified diets unsupplemented with riboflavin showed loss of appetite, weight loss, and ex
Nutrient Requirements of Mink and Foxes 15 treme weakness. Effects of deficiency started after about 2 weeks on the riboflavin-deficient diet (Leoschke, 1960~. Akimova (1969) stated that poor breeding results were ob- tained from animals fed diets deficient in riboflavin during growth, even though adequate amounts were fed thereafter. T7 · Gamin Young mink fed a purified diet required 1.2 mg of thiamin hy- drochloride per kilogram of dry feed, or 33 ,ug per 100 kcal ME (Leoschke and Elvehjem, 1959~. Short-term trials with fully grown mink Joergensen et al., 1975) showed marked increase of thiamin levels in muscles and heart when thiamin supple- ments from 2 to 24 milligrams per kilogram of dry matter were fed. The urinary excretion increased from 6 to 230 ,ug thiamin per animal per 24 hours. If the animals are fed raw fish containing the enzyme thi- aminase, thiamin is destroyed. Since thiaminase is heat-labile, the problem can be avoided by cooking the fish at 83°C (181°F) for at least 5 minutes before adding to the other diet ingredients (Gnaedinger and Krzeczkowski, 1966~. Another practical procedure is to include thiaminase-containing fish only on alternate days and give a thiamin supplement. Table 15 presents a list of fish containing thiaminase. Oregon studies showed that the diet consumed by the fish has an important bearing on whether thiaminase will be present (Stout et al., 1963~. That is, fish listed as thiaminase-free may ingest thiam- inase-containing fish and consequently create a secondary thiamin deficiency. In Scandinavia, when thiaminase-con- taining or ensiled fish are used at a level higher than 10 percent of the diet (wet basis), the urinary excretion of thiamin is monitored and not allowed to go below 150 ,ug per animal per 24 hours (G. Joergensen, National Institute of Animal Science, Hilleroed, Denmark, personal communication, 1978~. Signs of Deficiency Thiamin deficiency was first observed in adult mink fed Columbia River smelt (Long and Shaw, 1943~. The first obvious sign was failure to eat; emaciation and weak- ness rapidly followed. After 6 or 7 days, affected animals ex- perienced convulsions, which led to a state of collapse and in- ability to move. Diarrhea usually accompanied the last stage of the disease, and the fur on the posterior parts became coated with thick, black fecal excretions. This final stage lasted only a few hours, after which death occurred. Mink kits started on a thiamin-deficient purified diet at 8 weeks of age began to show thiamin deficiency (Chastek pa- ralysis) in 3 weeks (Leoschke and Elvehjem, 1959b). Signs were anorexia, loss of weight, lack of muscle coordination, ex- treme weakness, and, finally, paralysis and death. Animals displaying anorexia, loss of coordination, and con- vulsions due to thiamin deficiency may recover following a single intraperitoneal injection of thiamin hydrochloride solu- tion. If mink are still eating, supplementing feed with thiamin will restore the animals to good health. vitamin Bi2 A level of 30 ,ug per kilogram of dry diet, or 0.8 ,llg per 100 kcal ME, has been found to meet the requirement for growth (Leoschke et al., 1953; Leoschke, 1960~. The actual require- ment may be lower. This requirement is usually met by practi- cal mink diets containing large quantities of animal protein. Signs of Deb ency Mink affected by experimental vitamin BE deficiency show anorexia, loss of weight, and severe fatty degeneration of the liver (Leoschke et al., 1953~. Other Nutrient Factors Although no definitive work has been done on inositol, a level of 250 mg per kilogram of dry feed was apparently adequate for mink that were fed purified diets (Leoschke, 1960~. Fin- nish investigations Uuokslahti et al., 1978) confirmed Russian recommendations of giving mink a supplementation of 20-40 mg choline per animal per day. In the actual experiment, 40 mg choline chloride could prevent fatty liver and improve the hepatic function in mink. MINERALS General The relative requirements for mineral elements by mink cover an exceedingly wide range. For example, satisfactory produc- tion results (Kangas, 1974) have been obtained from mink ra- tions containing over 3,000 times as much calcium as copper. All mineral guidelines are given on a dry matter basis unless otherwise stated. The composition of mineral sources com- monly used as feed supplements is shown in Table 14. Calcium and Phosphorus For growing mink, calcium-to-phosphorus ratios between 1.0:1.0 and 1.2:1.0 have been recommended (Bassett et al., 1951~. Under optimal conditions the minimum calcium and phosphorus requirement may be below 0.3 percent (Bassett et al., 1951~; however, in practice it appears that growing mink require 0.4 to 1.0 percent calcium and 0.4 to 0.8 percent phos- phorus if vitamin D is provided at a concentration of 820 IU/kg dry feed and the calcium-to-phosphorus ratio is be- tween 0.75:1.0 and 1.7:1.0 (Rimeslatten, 1966b). Signs of Deficiency When the diet is deficient in calcium or phosphorus, bone growth is abnormal. Signs of Excess Within 10 days after they are placed on a ra- chitogenic diet high in calcium and low in vitamin D and phosphorus, mink kits experience difficulty in walking (Smith and Barnes, 1941~. They tend to crawl, and the condition becomes more severe until they are unable to stand. Enlarge- ments of the ribs at the costochondral junctions are evident. The spinal column in the thoracic region becomes concave (lordosis). The leg bones bend and enlarge at the ends. The ash contents of the dry fat-free femurs are 22 to 30 percent, com- pared with 60 to 64 percent for normal animals.
16 Nutrient Requirements of Mink and Foxes Sodium and Chlorine (SaltJ There are no dam on the minimum requirements of the grow- ing mink for sodium and chlorine; however, 0.5 percent salt in the wet feed (Hartsough, 1955) or 1.3 to 1.5 percent salt in the dry diet (Glem-Hansen, National Institute of Animal Science, Hilleroed, Denmark, personal communication, 1978) has been suggested for pregnant and nursing females to prevent "nursing sickness," a condition that sometimes occurs during the latter stages of lactation. Sodium and chloride re- quirements at other times may be lower. Excessive salt intake is harmful. For example, Perel'dik et al. (1972) suggest that 1.5 percent added salt (dry basis) fed during growth results in reduced reproduction during the following breeding period; however, supporting data were not presented. Problems of salt toxicosis may be aggravated by reduced water intake. Potassium In the absence of precise requirements, Wood (1962) has sug- gested an amount equivalent to approximately 0.3 percent potassium for breeder and grower diets. Since potassium is plentiful in most plant materials, it may be expected to be ade- quately supplied in mink diets containing normal amounts of cereal (10 to 30 percent). Magnesium Considerable diversity of opinion exists concerning recom- mended minimum required levels of magnesium. Wood (1962) has suggested an amount equivalent to 440 and 396 mg/kg in breeder and grower rations, respectively, while the data of Warner et al. (1964) suggest 625 mg/kg to be adequate for normal growth on a purified diet. Evidence has not been presented that magnesium deficiency is a serious threat to ranch mink. The level of 440 mg/kg magnesium is tentatively recommended for mink diets in the absence of more definitive data. Some antagonism is recognized among magnesium, cal- cium, and phosphorus. Thus excesses of calcium or phospho- rus in the diet may decrease the absorption of magnesium, and vice versa (Glem-Hansen, National Institute of Animal Sci- ence, Hilleroed, Denmark, personal communication, 1978~. Iron The problems of providing adequate dietary iron to mink have been dramatized by the occurrence of a specific iron-defi- ciency syndrome, cotton fur or cotton pelt (Figures 6 and 7~. The precise amount of iron required by mink is not known, but if no interfering factors are present, 20-30 ppm iron is con- sidered adequate (Ahman, 1966, as cited by N. Glem-Hansen, National Institute of Animal Science, Hilleroed, Denmark, personal communication, 1978~. Glem-Hansen (National In- stitute of Animal Science, Hilleroed, Denmark, personal com- munication, 1978) has suggested 60 ppm, while Wood (1962) suggested an amount equivalent to 88 and 79 ppm iron for breeder and grower diets, respectively. Typical Scandinavian mink diets contain 156-352 ppm iron, well above this level (N. FIGURE 6 Cotton fur in mink. Pelts are parted to show underfur. Left: Cotton fur. Right Normal fur. SOURCE: F. M. Stout, Oregon State University, Corvallis. Glem-Hansen, National Institute of Animal Science, Hille- roed, Denmark, personal communication, 1978~. Feeding high levels of raw marine fish of the cod (Gadidae) family such as Pacific hake, Atlantic whiting, and coal- fish may result in severe anemia and cotton fur. Freezing the raw fish appears to accentuate the problem, while heating it to 93°C (200 °F) destroys or inactivates the causative factor (Stout et al., 1960a). Very high levels of trimethylamine oxide (TMAO) are present in such fish, and this compound is broken down by an enzyme present in the fish digestive tract to yield several products, including formaldehyde (FA) (Amano and Yamada, 1964~. Both TMAO (Ender et al., 1972) and FA (Costley, 1970; Wehr et al., 1976) have been identified as causative factors of cotton fur. FA has been shown to interfere with iron absorption in rats, and feeding FA to mink on a non- fish diet containing no TMAO has produced severe anemia and cotton fur. The difficulty can be overcome by supplying iron parenterally (Stout et al., 1960b); however, feeding of iron supplements has met with mixed success. Scandinavian researchers Ender et al. (1972) and Skrede (1974) report ferric glutamate and ferrous fumarate are satisfactory supplements for preventing dietary iron deficiency. However, ferric gluta- mate has been tested with negative results in the United States (Wehr et al., 1976~. Ferrous fumarate (200 ppm iron added to the diet) reduced but did not eliminate anemia and cotton fur caused by feeding FA or 55 percent Pacific hake (Adair et al., 1974~. Signs of Deficiency The most easily recognizable sign of iron deficiency in mink is cotton fur, an almost complete lack of pigmentation of the underfur. In addition, a microcytic-hypo- chromic anemia, severe emaciation, growth retardation, and rough pelage may occur (Stout et al., 1960a) (see Figures 6 and 7~. If anemia is present during critical early phases of fur
Nutrients Requirements of Mink and lToxes 17 growth, cotton fur is likely to develop. The earlier and more severe the anemia, the more pronounced the fur defect. Zzinc Wood (1962) has suggested levels equivalent to 66 and 59 ppm zinc on a dry matter basis for breeder and grower diets, re- spectively. In practice these levels were met without supple- mentation in typical Finnish mink diets, which contained 57-94 ppm zinc (Kiiskinen and Makela, 1977~. Since zinc has been reported to be transported through the skin (Keen and Hurley, 1977), mink maintained in galvanized wire cages might ab- sorb some zinc from this source. Signs of severe zinc deficiency have been reported in rats (Hurley and Mutch, 1973), but spe- cific evidence of zinc deficiency in mink is lacking. Manganese The minimum requirement of manganese for normal mink is not known. Wood (1962) recommends levels corresponding to 44 and 40 ppm for breeder and grower diets, respectively. These levels were obtained by analysis of adequate diets com- monly fed to mink on the west coast of the United States and Canada. Signs of Deficiency Manganese deficiency has been espe- cially noted in pastel mink, where it results in symptoms of "screw necks'' or head tilting. This is a result of a birth defect in which the otoliths (gravity receptors in the inner ear respon- sible for maintenance of equilibrium) are reduced in size or absent. Animals displaying this defect have extreme difficulty in swimming and, depending upon extent of defect, may be completely unable to maintain equilibrium and consequently drown. The syndrome can be prevented by 1,000 ppm man- ganese supplementation to the mother during embryonic de- velopment. Additionally it has been suggested that a slight increase in litter size may accompany such manganese supple- mentation (Erway and Mitchell, 1973~. Copper The recommended level for copper in the mink diet is 4.5-6.0 ppm (Glem-Hansen, National Institute of Animal Science, Hilleroed, Denmark, personal communication, 1978~. In gen- eral the copper requirement is adequately met by typical mink diets containing fish (Kiiskinen and Makela, 1977~. Iodine Presence of marine fish in the diet usually implies adequacy of iodine. Wood (1962) has suggested a level of 0.2 ppm for breeder and growth diets as adequate iodine levels. Normal fish-containing mink diets approximate 2.4-6.4 ppm iodine (Kiiskinen and Makela, 1977~. Selenium Data are not available on the minimum requirement for sele- nium; however, it is assumed that typical mink diets, espe- cially those containing fish, supply this trace element in suffi- cient quantities. Kiiskinen and Makela (1977) have reported several Finnish mink diets to contain 0.05-0.42 ppm selenium in the dry matter. Stowe and Whitehair (1963) determined FIGURE 7 Left: Carcass of normal mink. Right Carcass of cotton that 0.1 ppm selenium added as sodium selenite to a tocoph fur mink. Note the anemic condition of the carcass on the right. erol-deficient basal diet prevented all but minor tocopherol SOURCE: F. M. Stout, Oregon State University, Corvallis. deficiency lesions in mink (see section on vitamin E).