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OCR for page 2
Determining
Nutritional
Requirements
The nutrient requirements listed in this publication are recom-
mendations based on experimental evidence. Results of studies
on nutrient requirements are reported in the text in the units in
which they were originally published. The tables on nutrient
requirements present the values on the basis of comparable
digestibility and energy levels. Methods of calculation or
estimation are shown in the appendix of each table. In gen-
eral, the investigators who provided such evidence followed
standard procedures:
· Conclusions were based on the performance of groups of
animals.
· Performance responses, such as gains in body weight or
efficiency of feed conversion, were arrived at on the basis of
average values from such animal groups.
· Deficiency signs, when used as criteria of nutrient inade-
quacy, relate to appearance of such signs in an experimental
group and complete absence of signs in groups receiving the
specific nutrient considered.
The subcommittee believes that the values stated herein for
the various nutrients will permit maintenance of normal
health and productivity in animals. It must be recognized,
however, that adequate nutrition is dependent on other fac-
tors in addition to the diet composition per se. While the
values given have not been increased by any arbitrary "safety
factors," fur farmers or feed manufacturers catering to them
may wish to increase the concentrations of nutrients to offset
effects of stress factors such as extremes of weather or in-
cidences of certain diseases or parasitism. Such increases may
be particularly applicable in cases of nutrients that are known
to be unstable and subject to deterioration in feed storage, pro-
cessing, or handling.
Recommendations on nutrient requirements are necessarily
related to the size of individual animals and to their specific
production activities, e.g., reproduction, lactation, growth,
furring. Unfortunately, base data on the nutrient needs for
specific physiological states are often lacking. In practice,
although production activities throughout an animal unit may
be reasonably consistent, the sizes of individual animals may
vary considerably. In particular, because of the great dif-
ferences in size and growth rates of males and females, specific
requirements have been given separately for the two sexes.
Consequently, the data presented may need to be adjusted
and should, therefore, be treated as guides to adequate nutri-
tion, rather than fixed standards to be rigidly followed.
Requirements are expressed on three bases: percentage of
dietary dry matter (DM), or amount per kilogram (kg) of DM
fed (Tables 1 and 3), daily nutrient requirements per animal
(Tables 2, 5, and 6), and amounts per 100 kilocalorie (kcal)
metabolizable energy (ME) (Table 4~. This last method of ex-
pression has been added because both mink and foxes are fed
varying amounts of fat, and this has a strong influence on
energy concentration of the total diet. When the energy con-
centration is increased, other nutrient contents must be in-
creased also, as the tendency will be for the animals to con-
sume lower quantities of the diet. This matter is discussed in
the following section.
NATURE AND FUNCTION OF ENERGY:
ITS CENTRAL ROLE IN NUTRITION
Energy is not itself a nutrient but is, rather, a property con-
tributed to diets by the three macronutrients: fats (lipids), car-
bohydrates, and proteins; it is measured as a physical property
and expressed in either kilocalories (kcal) or kilojoules Skid.
One kcal is equivalent of 4.184 k]. Of these three energy sup-
pliers, the most concentrated source is fat, a unit weight of
which supplies more than twice as much energy as the same
weight of carbohydrates or proteins.
The animal requires feed energy for body heat, for body
biochemical reactions, for physical activity, and, as the life-
stage situation dictates, for one or more of the following:
growth, fur production, reproduction, and lactation. In the
absence of adequate available energy supplies, the perfor-
mance of the animals in these life phases will be suboptimal.
Thus, as in all other animal species, the role of feed energy is
central to the metabolism and performance of mink and foxes.
Failure to recognize this vital fact in much of the earlier ex
2
OCR for page 3
perimentation on nutritional requirements of mink very
seriously limits the applicability of some of the data and the
confidence in the conclusions drawn from those studies.
Responses to improved levels of various nutrients may be
masked or biased because of insufficient energy supplies in test
diets. Unfortunately, the reports of numerous mink-feeding
experiments, especially those evaluating the use of practical
feedstuffs, lack clear statements on the energy content of the
diets involved. Subsequent calculations of approximate energy
content of such diets, where published information made this
possible, have suggested that many of the reported shortcom-
ings in performance were due, at least in part, to inadequate
dietary energy concentration.
Similarly, many studies on requirements of protein or of mi-
cronutrients or on responses to nonnutrient additives or con-
taminants have used diets either too low or entirely uncon-
trolled in energy content. Reported results from such
investigations may, thus, be unreliable or misleading.
Recognition of the central role of energy has led to the prac-
tice of expressing nutrient requirements and recommendations
on the basis of energy (i.e., nutrient-to-energy ratio). Insofar
as practically possible, that principle will be followed in this
publication.
EXPRESSION OF ENERGY CONTENT OF
DIETS AND ENERGY REQUIREMENTS
Several methods of stating energy content of fur animal diets
and the energy needs of the animals have been used by dif-
ferent investigators; this has posed difficulties for those
wishing to interpret and compare statements and has caused
confusion in making practical application of the information.
Figures for energy values of feeds have been stated in three
different ways: (1) gross energy (E), which is the total com-
bustible energy of feeds determined in a bomb calorimeter; (2)
digestible energy (DE), which is that portion of the feed E that
does not appear in the feces; and (3) metabolizable energy
(ME), which is that portion of the feed E that is utilized by the
animal for maintenance, production, and energy storage, as it
is not lost in either feces or urine. ME, it is agreed, is the best of
these measures.
Whichever of the three measures is used, energy is most ap-
propriately expressed as kilocalories per gram (or per 100 g, or
per kilogram) of dry matter in the feed.
Among the many forms used for stating requirements or
recommended intakes of energy by the animals are the follow-
ing:
.
1. in relationship to composition of the ration kcal of E or
DE OF ME per stated weight (1 g or 100 g or 1 kg) of diet dry
matter.
2. daily energy intake in relationship to body size of the
animal kcal of E or DE or ME per 100 g (or per kilogram) of
body weight.
3. daily energy intake in relationship to metabolic body
size (MBS) of the animal kilocalories of E or DE or ME per
kilogram of metabolic body size.
Nutrient Requirements of Mink and Foxes 3
Much scientific work has shown that the most suitable basis
for expressing requirements of energy in an animal is the
metabolic body size (MBS) of the animal, rather than the ac-
tual body weight (BW). MBS, a concept of the metabolizing
mass of the body, is defined as body weight (in kilograms)
raised or calculated to the 0.75 power or, as commonly ex-
pressed: MBSkg = BWkg0 75 (Kleiber, 1947~. This basis of MBS
is one that does not lend itself readily to practical applications,
largely because of the introduction of a concept and a calcula-
tion with which mink producers may not be familiar. In such
situations, actual body weight (BOO) is a more familiar and
comprehensible basis; consequently, practical recommenda-
tions may be more usefully converted to and expressed on the
BW basis, even though investigational results may have been
expressed originally on the basis of MBS. This practice has
been followed in the present publication.
Despite the biological superiority of ME as a measure of
energy, especially for research purposes, its practical use is
severely limited by the paucity of available data on ME values
of common feedstuffs and diets for mink and foxes. (It should
be emphasized that published ME values of foodstuffs for om-
nivores such as poultry or swine are not valid for the naturally
carnivorous mink.) Many more data on E of feedstuffs are
readily available, and additional data can be much more eas-
fly determined. (E values are independent of species.) In view
of the fact that ME values are not strictly additive, i.e., the
ME value of a mixed diet is not necessarily the sum of the ME
values (even if available) for all the ingredients, it can be
argued that relatively little error will be introduced by multi-
plying E values for mixed diets by a factor representing a
typical experimentally determined ratio between the ME and
the E values for such diets. E values are additive. Evans
(1967b, 1976, 1977) has found, in numerous experiments, that
ME values of conventional North American mink diets usually
range from 72 to 85 percent of E values, the overall average
being 77 percent. ME as a proportion of E was usually greater
for high- than for low-energy diets and for conventional diets
than for diets with more vegetable protein. Chwalibog et al.
(1979) in Denmark found ME values to be 80 percent of E for
diets of low and moderate protein content (18 percent and 34
percent, respectively, of E), but this fell to 72 percent for diets
in which 61 percent of the E was supplied as protein. There is
obviously general agreement between the Danish and North
American (Canadian) values.
Considerably more data are available for DE of feedstuffs
than for ME, but DE data are still much less available than E
data. DE values also are not completely additive and will vary
with ration composition and quality of ingredients. Literature
reports of digestibility of E of mixed rations ranges from ap-
proximately 65 to 88 percent, the lowest generally being for
low-energy rations high in vegetable sources and the highest
for high-energy rations of high-quality conventional, predom-
inantly animal, ingredients. For purposes of estimating
dietary E, the following E values for protein, fat, and car-
bohydrate of 5.7, 9.5, and 4.0 kcal/g, respectively, may be
used. Calculations for estimating DE and ME from these
figures are presented in Tables 8 and 9.
The expressions of energy requirement in relation to animal
weight are, of course, often much more useful for strict
OCR for page 4
4 Nutrient Requirements of Mink and Foxes
research purposes than are the expressions on the basis of feed
composition but, again, for practical purposes the latter are
often more readily comprehensible and more useful. Thus
energy recommendations in this report are presented in both
forms.
GROWTH RATES
Growth curves for mink (Figures 1 and 2) and for foxes
(Figures 3 and 4) are presented as indicators of normal, ex
2400
2200 _
2000 _
1 800 _
1600 _
E 1400 _
-
~ 1 200 _
~ 1~ _
_
600 _
400 _
200 /'
o
0 30 60 90
/'
~//~''
/ '''
1 1 1 1 1 1
120 150 180 210 240
AGE (days)
FIGURE 1 Standard dark mink growth curve. SOURCE: N. Wehr,
J. E. Oldfield, and J. Adair, Oregon State University, Corvallis.
1 1 00
1 000
900
800
700
-
600
3 500
400
300
200
100
n
pected performance. The various color types of mink are not
differentiated in these figures, as it is now assumed that they
will grow similarly if given adequate nutrition in satisfactory
environments. Early growth is extremely rapid for the young
mink and constitutes a period of critical nutritional demand.
This period is illustrated separately in Figure 2 to allow more
detail than is possible in a comprehensive growth curve. Sepa-
rate growth data are presented for silver and blue foxes in
Figures 3 and 4, respectively.
6000
5000 _
N,dle
2000 _
1000 .
//
//
/~/
Aft'
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
AGE tweaks)
FIGURE 3 Silver fox growth curve. SOURCE: FI. Rimeslatten,
Agricultural College of Norway, Vollebekk.
7000:
;
1 _
1 _
J ~I I I I
0 1 0 20 30 40 50 60
AG E (days )
6000 _
5000 _
/ o, _
/// 3
,7/ ~ 3000 _
/
_~~
Mild
FIGURE 2 Standard dark mink early growth curve. SOURCE: N.
Wehr, J. E. Oldfield, and J. Adair, Oregon State University, Cor-
vallis.
2000 _
1000
o
it//
//
//
//
//
//'
/
if'
//
//
//
~///-
M`~o /
0 2 4 6 8 10 12 14 16 18 20 22 24 26
AGE (weeks)
FIGURE 4 Blue fox growth curve. SOURCE: H. Rimeslatten, Agri-
cultural College of Norway, Vollebekk.
Representative terms from entire chapter:
growth curve
