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OCR for page 24
Foxes :
Recommenclec!
Dietary
Allowances
ENERGY
The general principles discussed previously for mink apply
equally well to foxes. The provision of adequate energy is
a primary requirement, and it is logical and necessary to re-
late the diet content of nutrients to the energy density of the
diet. For explanation of energy-related terms see pages 3
through 4.
Published information on energy requirements is quite
limited. The use, by different authors, of different methods of
expressing recommendations and intakes creates difficulties in
the comparisons of even these limited data.
Early estimates of the daily gross energy (E) requirements of
mature foxes in North America were 111 to 121 kcal per kilo-
gram of body weight (Palmer, 1928) and 121 kcal per kilo-
gram of body weight (Hodson and Smith, 1942~; the latter
authors also expressed their estimate of energy requirement as
2,102 kcal per square meter of body surface. The previous edi-
tion of this publication (NRC, 1968), on the basis of the figure
of 121 kcal per kilogram of body weight and estimates of aver-
age animal weight and daily feed intake, recommended that a
maintenance diet for foxes should contain 3,227 kcal of E per
kilogram of dry matter. Insufficient data were available to war-
rant recommendations for growth, pregnancy, or lactation.
Perel'dik et al. (1972), using data from various Russian ex-
perimental measurements of energy conversion by adult foxes,
calculated the requirements of metabolizable energy (ME) for
maintenance and claimed that these requirements were in
agreement with those determined by Hodson and Smith
(1945) and others, although expressed in different terms. The
figures reported by Perel'dik et al. (1972) for adult mainte-
nance were as follows:
June to August
September to October
November
December
- 93 kcal of ME per kilogram live weight
- 81 kcal of ME per kilogram live weight
- 72 kcal of ME per kilogram live weight
- 65 kcal of ME per kilogram live weight
More data are available on the requirements of female than
of male adult foxes. Perel'dik et al. (1972) listed recommended
intakes of ME for female silver foxes and for male and female
blue foxes of typical weight under practical conditions
throughout the year. These recommendations, summarized in
Table 16, include an additional variability allowance of 10
percent for "farming conditions." Although there are a few in-
consistencies, the recommendations reflect the preference for
reduced energy intake in the winter months with the intent of
producing thinner animals for the breeding periods, as well as
the fact that the requirements of blue foxes are slightly higher
than those for silver foxes, at least at certain times of the year.
Although a requirement for additional energy intake during
pregnancy is commonly recognized, there is little agreement
on the additional levels required. Perel'dik et al. (1972j
reported a variety of recommendations from different investi-
gators. Some investigators recommended different energy in-
takes in the first and second halves of pregnancy, e. g.,
Abramov (1950) recommended 495 and 630 kcal of ME daily
for these respective periods. However, Firstov and Kharitonov
(1957) favor 560 kcal of ME per day for the whole period.
During the lactation period the energy requirement of the
female to provide adequate milk for the suckling pups is pro-
portional to the number of pups and increases as the age of the
pups increases. Various workers have, therefore, recommended
that lactating females receive incremental energy intakes per
pup suckled, with the increments increasing successively per
week or per 10-day interval of the lactation period. Perel'dik
et al. (1972), combining data from Rimeslatten in Norway
and from practice on Russian fur farms, recommended that
the energy intake of lactating females consist of an allowance
of 450 kcal ME per day for maintenance plus the following
variable amounts for successive 10-day period of lactation:
10-Day Periods Additional Energy
of Lactation per Pup Daily (kcal ME)a
1st period
2nd period
3rd period
4th period
5th period
6th period
52
123
195
292
392
450
a Over the whole lactation period, the above recommendations
represent an average of 250 kcal ME per pup per day.
24
OCR for page 25
Nutrient Requirements of Mink and Foxes 25
Diets supplied to fox pups after weaning must supply the re-
quirements of energy for both maintenance and continuing
growth. As the body weight increases, the maintenance re-
quirement steadily increases up to about the seventh month of
age. In addition, sufficient energy must be added to provide
for growth that will occur at a gradually declining rate from
the second to the eighth month of age. Perel'dik et al. (1972),
working from Russian calorimetry data on maintenance re-
quirements and calorific values of the weight increases ob-
tained by Perel'dik (1950), calculated the total energy allow-
ances for growing silver fox pups. These allowances, as shown
in the following table, include an extra practical allowance of
15 percent for "farm conditions" and apply to both sexes. In
practice, these allowances would be obtained by the pups
from varied intakes of a diet of appropriate energy density.
Somewhat higher allowances, largely because of a 30 percent
higher maintenance requirement and a faster rate of growth,
were recommended for blue foxes.
Age of Pups
(months)
Live Weight at
Beginning of
Month (kg)
Total ME
Allowance
(kcal/day)
2-3
3-4
4-5
s-6
6-7
7-8
1.80
3.00
4.10
s.oo
s.7s
6.00
4so
see
630
660
s60
490
Studies by Mamaeva (1958) indicated that the body weights
of foxes late in the growing period were similar under two dif-
ferent patterns of energy feeding, moderate early levels versus
high early levels. The latter pattern, however, produced faster
early weight increases and resulted in animals that were
longer, taller, and lower in body fat than did the other pat-
tern, which produced more uniform weight increases over the
growing period.
Moderate deficiency of energy intake causes retardation or
cessation of growth; severe deficiency results in emaciation.
The fur may be dull if the energy supply is inadequate. Milk
yield in lactating animals may be reduced by inadequate
energy intake.
FATS
Widely different levels of fat have been reported to give satis-
factory results. Obviously, variations in the proportions of fat
in the dry matter of the diet will be the major factor in adjust-
ing the energy density of diets.
Up to 44 percent of fresh fat was used in fox diets without
any detrimental effects (Bassett, 1951~. Rancid fat should not
be used, as it can create a vitamin E deficiency. Perel'dik et al.
(1972) recommended that fat be used to meet particular dietary
requirements, at levels supplying from 23 to 49 percent of the
digestible energy (DE). Rimeslatten (1976) reported that the
ME energy from fat had a higher productive value than that
from either carbohydrates or protein.
It has been estimated that silver foxes should receive a
minimum of 2 to 3 g of essential fatty acids (linoleic and
linolenic acids) daily to prevent hyperkeratosis and dandruff
(Ender and Helgebostad, 1951~.
CARBOHYDRATES
Limited studies of the possible requirements for carbohydrates
or of the possible limitations of their use in fox diets have been
conducted. Earlier reports (Schaefer et al., 1947a; Tove et al.,
1949) indicated that an experimental diet containing up to 66
percent sucrose was apparently adequate. Most practical diets
for foxes will contain much lower levels of carbohydrate, pri-
marily starch. Perel'dik et al. (1972) recommended, for a vari-
ety of diets for silver foxes, carbohydrate levels supplying be-
tween 14.3 and 35.0 percent of the DE; for blue foxes, the
recommended proportions of DE supplied by carbohydrate
ranged from 12.4 to 31.3 percent.
It has been generally observed that foxes can utilize carbo-
hydrate better than can mink (Rimeslatten, 1951), and fox
diets usually contain higher levels of carbohydrate than do
those for mink. Rimeslatten (1976) has generalized that the
percentage of ME supplied by carbohydrate can be 5 to 10 per-
cent higher in fox than in mink diets.
PROTEIN
A detailed commentary on the critical importance of protein
quality in fur animal nutrition is presented in the mink section
of this report.
Maintenance
Studies by Rimeslatten (1976a) indicate that, with proper
energy balance, there are no significant differences in body
weight of blue foxes raised from weaning to pelting on diets
containing from 22 to 45 percent of ME from digestible pro-
tein (for calculations see Table 9~. Thus it appears that for the
blue fox the maintenance protein requirement, as opposed to
that required for growth, would be met by diets containing 22
percent of ME from digestible protein.
Gestation
Rimeslatten (1976b) has indicated that estrus, breeding, and
reproduction of blue foxes are not significantly influenced by
alterations in digestible protein concentration ranging from
25 to 40 percent of ME. A slight reduction in litter size at birth
was observed when vixens were fed protein levels below 31-32
percent of the ME; however, this difference was not judged to
be significant. On the basis of these observations, Rimeslatten
recommended a minimum protein level of 30 percent of ME.
Lactation
Rimeslatten's studies (1976b) have indicated reduced weight
gains of fox pups when their dams received diets containing
protein levels below 30 percent of ME.
OCR for page 26
26 Nutrient Requirements of Mink and Foxes
Early Growth (7-16 Weeks)
Harris et al. (1951a) found that more than 40.7 percent pro-
tein (dry weight basis) was required to attain maximum
nitrogen storage in fox pups between 7 and 23 weeks of age.
However, growth of foxes on a diet containing only 24.5 per-
cent protein was equivalent to that of foxes on higher protein
levels. Rimeslatten (1976b) has observed that fox pups raised
on diets containing less than 28-30 percent ME from digestible
protein attained normal body weight but displayed reduced
body length.
Late Growth and Fur Development (16 Weeks to PeltingJ
Rimeslatten (1976b) has recommended a level of 25 percent
ME from digestible protein for the period from 16 weeks of
age to pelting. Fur development and quality were not signifi-
cantly affected by dietary protein concentrations within the
range of 26 to 38 percent ME from digestible protein.
Data presented in Tables 3 and 4 represent minimum pro-
tein requirements of foxes during different phases of the life
cycle. Fox producers and fox pellet manufacturers may wish to
include higher concentrations of protein, thus providing a
margin of safety above the minimum protein requirement.
FAT-SOLUBLE VITAMINS
Vitamin A (RetinolJ
The minimum amount of vitamin A necessary to prevent ner-
vous signs in young foxes lies between IS and 25 IU per kilo-
gram of body weight per day (Smith, 1942~. This vitamin is
not stored in the liver until 50 to 100 IU vitamin A per
kilogram of body weight per day are fed.
Although a fox can apparently utilize carotene as a source of
vitamin A, the carotene is poorly assimilated (Coombes et al.,
1940~. When carotene is being used to satisfy vitamin A re-
quirements of foxes, a conversion factor of 6.0 should be ap-
plied to compensate for the inefficiency of utilization of caro-
tene (Bassett et al., 1946~.
Until further data are available, it is recommended that
growing foxes be supplied at least 100 IU of vitamin A, or 600
IU (360 ,ug) of §-carotene, per kilogram of body weight per
day. During rapid growth, the requirement would be 66 IU of
vitamin A per 100 kcal ME.
A fox can tolerate large doses of vitamin A (Helgebostad,
1955~. A dosage of 40 IU of this vitamin per gram of body
weight, administered daily over a period of 3 to 4 months, pro-
duced no toxic signs; 200 IU per gram of body weight, admin-
istered daily over a period of 1 to 2 months, produced signs of
hypervitaminosis A in pups. Signs of excess were anorexia,
bone changes with exostoses, decalcification and spontaneous
fractures, loss of fur, exophthalmia, cramp, and local hyper-
esthesia of the skin.
Signs of Deficiency Foxes fed a diet deficient in vitamin A
develop a series of nervous derangements, usually manifested
in this order: first, trembling or cocking of the head; next,
unsteadiness (resulting from a disturbed sense of balance);
then a tendency to run in circles (Smith, 1942~.
Often, in attempting to observe an object behind them, de-
ficient animals, instead of turning around in the normal
fashion, jerk their heads over their shoulders, lose their bal-
ance, and fall over.
These signs usually begin 1 to 5 months after the animals are
placed on a diet deficient in vitamin A. Later, certain ani-
mals, after being excited, exhibit increased nervousness until
they pass into coma or tetany, which lasts S to 15 minutes. The
nervous signs are not eliminated by feeding or injecting vita-
min A. Typical xerophthalmia occurs after 4 to 6 months.
The deciduous and permanent teeth of foxes deficient in
vitamin A are present in the same socket, and in many in-
stances the adult incisors are small, discolored, and chipped or
broken on the corners (Bassett et al., 1946~. Another sign is a
high incidence of urinary calculi.
Vitamin D
Harris et al. (19Slb) found that a diet of natural foodstuffs that
assayed 0.82 IU of vitamin D per gram, or 22 IU per 100 kcal
ME, was adequate for growing foxes; the diet was fed without
a vitamin D supplement. A daily supplement of 200 IU of vita-
min D per kg of body weight with this diet did not prevent ra-
chitic changes when calcium or phosphorus was deficient, and
it did not improve physiological responses at adequate mineral
levels. Vitamin D supplementation of practical fox diets,
therefore, does not appear necessary.
Signs of Deficiency Rickets can be produced in foxes by feed-
ing diets having low vitamin D content and abnormal cal-
cium-to-phosphorus ratios (Hanson, 193S; Ott and Coombes,
1941 Smith and Barnes, 1941; Harris et al., 1945, 1951b).
Signs of rickets in growing kits are generally seen between 2
and 4 months of age.
Vitamin E
Vitamin E requirements of foxes have not been determined.
However, it appears that when good-quality foodstuffs are
given, supplemental sources of vitamin E are unnecessary for
growth or reproduction. Vitamin E levels in the diet are re-
lated to the presence or absence of other nutrients and antioxi-
dants. (See discussion in sections on vitamin E and antioxi-
dants, mink section.)
Signs of Deficiency Experimental production of yellow fat
disease in foxes has been described (Ender and lIelgebostad,
1953~. The disease is often characterized by hemorrhagic
diathesis and red, swollen, hemorrhagic gastrointestinal mu-
cosa with or without ulcers. Calcium incrustations are found
in the endothelium of the large vessels and in the muscles and
kidneys.
Vitamin K
The requirements for vitamin K have not been determined for
foxes. Perel'dik et al. (1972) reports that, on farms where silver
OCR for page 27
and blue foxes were born with subcutaneous hemorrhages, the
enrichment of the diets of pregnant females with vitamin K
was beneficial.
WATER-SOLUBLE VITAMINS
ASCOTbiC Acid (Vitamin C)
Lack of vitamin C has no visible effect on the health of grow-
ing foxes or on the quality of their fur (Mathiesen, 1939, 1942~.
However, there is a relation between vitamin A and ascorbic
acid in the nutrition of foxes (Bassett et al., 1948), which sug-
gests that a deficiency of vitamin A in the diet will reduce tis-
sue synthesis of vitamin C below physiological requirements.
Biotin
In a study of biotin deficiency signs of foxes, Helgebostad et al.
(1959) used a diet that supplied a total of 30 percent of protein
as raw egg white. This diet was fed to pregnant foxes, with the
result that some of the young were born with changes in hair
color (Figure 10~. Some of those born with normal hair devel-
oped the changes in color after receiving the egg-white diet
themselves. The condition rapidly improved in all deficient
animals that were given 1 mg of biotin twice a week. At au-
topsy, the liver showed extensive fat infiltration in deprived
animals. There were also large amounts of sudanophilic sub-
stances in the kidneys and myocardium. This confirmed
earlier work (Gunn, 1948) in which 25 percent of raw egg
powder was used in the diet of fox pups as the source of animal
protein. Gunn found that deficiency signs developed after 12
to 15 weeks. The pups showed graying and loss of fur over the
body and tail, eye infections, and gray muzzles. Finally, the
legs became weak. Adding 5 percent of yeast to the diet or
pressure cooking the egg powder greatly reduced the signs.
Folic Acid
Folic acid is required in the fox diet. It is suggested that 0.2 mg
per kilogram of dry diet, or S.2 ,ug per 100 kcal ME, be ac-
cepted as the tentative requirement (Schaefer et al., 1947a).
Folic acid conjugates are incapable of replacing folio acid in
the fox diet (Tove et al., 1949~.
Signs of Deficiency Foxes fed a purified diet deficient in folio
acid develop anorexia, loss of body weight, and a decrease in
hemoglobin and in red and white blood cells (Schaefer et al.,
1947a). This condition causes death if it is not treated.
Niacin
Schaefer et al. (1947b) have suggested that foxes be fed 0.39 to
2.0 mg of niacin (as calculated from dose feedings) per kilo-
gram of body weight per day. It is suggested that 10 mg per
kilogram of dry diet, or 0.26 mg per 100 kcal ME, be accepted
as the tentative requirement.
Signs of Deficiency Foxes fed a purified diet deficient in nia-
cin show anorexia, loss of body weight, and typical black
Nutrient Requirements of Mink and Foxes 27
FIGURE 10 Biotin deficiency. The newborn fox pup on the left is
from a biotin-deficient dam that received a diet containing raw egg
white. Thin, gray pelt and deformed legs are apparent. A control diet
containing cooked egg white was fed to the dam of the pup on the
right, which is also newborn. SOURCE: A. Helgebostad, Veterinary
College of Norway, lIeggedal.
tongue, which is characterized by severe inflammation of the
gums and fiery redness of the lips, tongue, and gums. If the
animals are not treated with niacin, they develop severe diar-
rhea, pass into a coma, and die (Hodson and Loosli, 1942;
Schaefer et al., 1947b).
Pantothenic Acid
Schaefer et al. (1947b) have suggested that foxes require be-
tween 2.S and 15.0 mg of pantothenic acid per kilogram of
diet. Until further information is available, it is suggested that
the tentative requirement be 8.0 mg per kilogram of dry diet,
or 0.21 mg per 100 kcal of metabolizable energy.
Signs of Deficiency Signs of deficiency include cessation of
growth, and coma (Schaefer et al., 1947b). Death is sudden.
Necropsies reveal gross fatty degeneration of the liver, catar-
rhal enteritis, and cloudy swelling and congestion of the
kidneys.
OCR for page 28
28 Nutrient Requirements of Mink and Foxes
Riboflavin
Experiments designed to show the importance of some of the
B-complex vitamins in nutrition of foxes indicate that the min-
imum and maximum levels of riboflavin for pups are greater
than 1.25 and less than 4.0 mg per kilogram of diet (Schaefer
et al., 1947b). In other experiments, a basal diet calculated to
contain 1.3 to 1.6 mg per kilogram produced riboflavin defi-
ciency in the blue fox (Rimeslatten, 1958~. The requirement
per 100 kcal of ME is at least 0.1 mg for larger pups and 0.15
mg during pregnancy and lactation.
Signs of Deficiency Riboflavin deficiency in foxes results in a
decreased rate of growth within 2 weeks after the animals are
placed on a deficient diet (Schaefer et al., 1947b). After 3 or 4
weeks, signs of muscular weakness, chronic spasms, and coma
occur. When riboflavin is administered, animals will recover
within a few hours. If foxes are further maintained on the defi-
cient diet, opacity of the cornea and a decrease in pigment
production in the fur are noted.
Rimeslatten (1958) showed Mat a riboflavin deficiency will
develop in litters of blue foxes fed a diet containing a poor-
quality sun-dried eviscerated cod meal. Additions of B-complex
vitamins to the diet relieve the deficiency signs. When ribofla-
vin is omitted, pups on the diet develop fatty dermatitis, and
the fur becomes much paler (sometimes nearly white) in 5 to 7
weeks (Figure 11~. Part or all of the hair falls out, the eye lenses
become opaque, and muscular weaknesses develop. When a
B-complex vitamin supplement containing riboflavin is fed,
both dermatitis and muscular control improve in a few days.
In 1 to 2 weeks, a new pigmented pelt begins to develop. The
omission of B-complex vitamins other than riboflavin from the
supplement produced no harmful effects.
T~ ·
ntamin
The minimum requirement of mature foxes for thiamin
hydrochloride is 800 lug per kilogram of dry feed, or 21 jug per
100 kcal of ME (Harris and Loosli, 1949~. Kringstad and
Lunde (1940) found that 0.2 mg of thiamin per animal per day
is sufficient to prevent deficiency signs.
The minimum level of thiamin suggested for practical feed-
ing of foxes is 1.0 mg per kilogram of drv feed. or 27 up Der 1 no
kcal of metabolizable energy.
Signs of Deficiency Thiamin deficiency in foxes results in
anorexia, weakness, convulsions, and paralysis (Ender and
Helgebostad, 1939; Kringstad and Lunde, 1940~. Convulsions
may occur just before death, which usually comes 48 to 72
hours after the onset of neurological signs. In advanced stages
of the disease, foxes moan as if in great pain. At autopsy, the
liver usually exhibits severe degeneration. Bilateral vascular
lesions, found principally in the paraventricular gray matter
of the brain, are useful in diagnosing the disease.
Chastek paralysis is a deficiency disease of foxes and mink.
It occurs when certain types of raw fish (see Table 15) are in-
cluded in the diet (Green et al., 1941~. These fish contain the
enzyme thiaminase. When they are included in a mixed ra-
tion, the enzyme destroys the thiamin in the diet. The disease
~ ~_ ~ e ~ ~ ~
FIGURE 11 Riboflavin deficiency. Right after 7 weeks on a diet
deficient in riboflavin, 12-week-old blue fox showed depigmentation,
shedding of fur, and dermatitis. Left: littermate was fed the same diet
supplemented with riboflavin. SOURCE: H. Rimeslatten, Agricul-
tural College of Norway, Vollebekk.
can be prevented or cured by feeding or injecting thiamin.
When whole carp is fed to foxes at a level of 20 percent of the
wet diet, 5 to 10 mg of thiamin hydrochloride per animal per
day are required to prevent Chastek paralysis (Green et al.,
1941~. It is suggested that 0.5 to 0.75 mg of thiamin hydro-
chloride in sterile distilled water be injected subcutaneously
into each fox to cure thiamin deficiency and that subsequently
the animals be given a diet containing the recommended
amounts of thiamin (Harris and Loosli, 1949~. Cooking the
fish at 83°C (181°F) for at least 5 minutes destroys the thi-
aminase and renders them safe.
vitamin Be
A level of 2.0 mg of pyridoxine per kilogram of diet will pre-
vent signs of deficiency in foxes (Schaefer et al., 1947b). In the
absence of more critical information, it is suggested that 2.0
mg per kilogram of dry diet, or 50 ,ug per 100 kcal of ME, be
accepted as the tentative requirement.
Signs of Deficiency A pyridoxine deficiency results in ano-
rexia, cessation of growth, and a decrease in hemoglobin
(Schaefer et al., 1947b).
OCR for page 29
vitamin B12
No experiments to estimate vitamin BE requirements of foxes
have been reported. Practical diets for foxes usually contain
sufficient amounts of animal protein. Such diets and addi-
tional vitamin BE from intestinal synthesis should provide an
adequate supply of this vitamin.
M INK RAL S
Calcium and Phosphorus
The calcium requirement of the growing fox 7 to 37 weeks of
age is between 0.5 percent and 0.6 percent in the dry diet
(Harris et al., 1945, 1951b).
Additionally, the ratio between calcium and phosphorus is
important in the nutrition of foxes (Harris et al., 1951b). A
calcium-to-phosphorus ratio ranging between 1.0:1.0 and
1.7:1.0 appears to be satisfactory. Ratios outside this range
may result in improper growth of bone, even when the diet
contains large amounts of vitamin D.
Signs of Deficiency Fox pups on a rachitogenic diet develop
a stiffness of the rear legs and begin walking on their pasterns
rather than on their toes (Smith and Barnes, 1941~. Their leg
joints swell, and the leg bones become bent. The ash content of
the dry, fat-free ulnas decreases from a normal of 62 to 67 per-
cent to 36 to 47 percent. The long bones become soft and vas-
cular. Serum calcium falls from 10.8-11.8 mg per 100 ml to
7.2-9.0 mg after 8 weeks on the rachitogenic diet.
Harris et al. (1945) have supplied evidence that calcium-
deficient foxes show, progressively: lameness, recurrent spasms,
Nutrient Requirements of Mink and Foxes 29
crooked legs, arid enlargement of the cranial bones, especially
the maxillae and palatines (Figure 12~. The muzzle becomes en-
larged, the gums become swollen, and the teeth become loose.
Foxes on low-phosphorus diets reveal symptoms of lame-
ness, crooked legs, enlarged joints, and a mineral poverty of
the bones, shown by X-ray (Harris et al., 1951b). Occasion-
ally, an animal develops an undershot jaw.
Sodium and Chlorine
In the absence of data on the specific requirements of foxes for
sodium and chlorine, it has been recommended that the diet
be fortified with 0.5 percent sodium chloride (salt) calculated
on a dry matter basis (NRC, 1968~.
Iron
The minimum iron requirement of foxes is not known; how-
ever, uncooked fish of the cod family (such as Pacific hake,
Atlantic whiting, and coalfish) have been shown to interfere
with iron absorption in rats and mink (Costley, 1970~. An in-
creased requirement for iron has been observed in silver and
blue foxes fed air-dried cod (Rimeslatten, 1959~. In this case
supplementation of the diet with liver was reported to be
beneficial. Supplementation of the breeder diet with iron sul-
fate has been reported to reduce litter size (Goncharenko,
1976~. Iron deficiency signs include anemia and depigmenta-
tion of underfur (Rimeslatten, 1959~.
Cobalt, Copper, iodine, Manganese, and Zinc
In the absence of firm data on the minimum requirements of
foxes for these minerals, results of Soviet studies with trace
FIGURE 12 Calcium deficiency. Each of
these bones is a right humerus taken from a
female fox. The bone on the right was taken
from a fox that received 0.5 percent calcium
in its diet, plus sunshine. The others are from
foxes kept in the shade and fed (left to right)
0.16, 0.2, 0.3, 0.4, and 0.5 percent calcium in
the dry diet. SOURCE: L. E. Harris, Utah
State University, and C. F. Bassett, USDA.
OCR for page 30
30 Nutrient Requirements of Mink and Foxes
mineral fortification of standard fox diets are pertinent. All
values are in units of weight of supplement per kilogram of
animal body weight per day. Simultaneous supplementation
of the fox breeder diet with cobalt (0.5 mg CoCl2), manganese
(1.0 mg MnSO4), and zinc (0.2 mg ZnSO4) has been reported
to decrease pup mortality (Berzins, 1957~. However, superim-
posing copper (0.5 mg CuSO4) supplementation upon the pre-
vious treatment has been reported to increase pup mortality
(Berzins, 1967~. Supplementing the breeder diet with iodine
(0.05 mg KI), cobalt (0.5 mg CoCl2), and a considerably
lower level of copper (0.05 mg CuSO4) from 10 days before
breeding through pregnancy and lactation has been reported
to increase litter size (Zotova, 1968~. Low level cobalt (0.5 ,ug
CoCl2) and iodine (0.1 ,ug KI) supplementation of grower
diets was reported to increase pup size and improve fur quality
(Bukovskaya, 1969~. These experiences relate to a typical diet
of meat, fish, and cereal and may or may not be reproducible
in diets of other composition.
For a discussion of feed additives, disorders related to nutri-
tion, and toxic substances in the feed supply pertaining to fox
nutrition see pages 18 through 23.
Representative terms from entire chapter:
blue foxes
