Content uploaded by Robert B Rucker
Author content
All content in this area was uploaded by Robert B Rucker
Content may be subject to copyright.
Developmental Changes in Composition of Cats'
Milk: Trace Elements, Minerals, Protein,
Carbohydrate and Fat1
CARL L. KEEN,* BO LONNERDAL,*
MICHAEL S. CLEGG,* LUCILLE S. HURLEY,*
JAMES G. MORRIS.H QUINTON R. ROGERSJ AND
ROBERT B. RUCKER*
'Department of Nutrition, ^Department of Animal Science
and ^Department of Physiological Chemistry,
University of California, Davis, CA 95616
ABSTRACT The concentrations of iron, copper, zinc, manganese, calcium, mag
nesium, protein, carbohydrate and fat were analyzed in cats' milk during the course
of lactation. Cats' milk is different from most species in that the concentrations of iron,
copper, zinc and manganese are lower during the first 2 days of lactation than on days
3-7. After the initial rise in the concentration of these elements, the concentration of
iron decreased from 5.9 ng/ml to 3.0 fig/ml, with most of the decrease occurring
between days 8 and 21. Copper concentration declined from 1.6 /ig/ml to 0.8 /tg/ml,
with most of the change occurring between days 8 and 28. Concentration of manganese
increased during lactation, from 0.14 fig/ml to 0.39 fig/ml. Calcium concentration
increased rapidly during the first 3 weeks from 550 fig/ml to 1500 /xg/ml, with little
change thereafter. The magnesium concentration (~100 jig/ml) and zinc concentration
(~6 Mg/ml) were not affected by stage of lactation. Protein increased during lactation
from 4% to 7%, and fat from 3% to 5%, whereas carbohydrate concentration (=:4%)did
not change significantly. These data demonstrate that the nutrient intake of the kitten
changes markedly during the early neonatal period and that these changes should be
taken into account in evaluating studies of suckling cats. J. Nutr. 112: 1763-1769,
1982.
INDEXING KEY WORDS lactation •cats' milk •trace elements •miner
als •milk
The developing cat is a potential model for (protein, fat, carbohydrate) in cats' milk,
several types of nutritional, physiological and very little is known about the quantitative
biochemical studies. The early neonatal pe- and qualitative requirements of the young
riod is characterized by rapid changes in cat for trace elements (Fe, Cu, Zn, Mn) and
body composition. To understand the origins minerals (Ca, Mg). We were able to find one
and significance of these changes in body report in which the mineral composition of
composition, it is essential to obtain detailed cats' milk is discussed, although the data in
knowledge of the composition of cats' milk that report was from only two milk samples,
and its variation during the course of lacta- both of which were mature milk (1). We
tion, as this is the only source of nutrients have therefore analyzed the developmental
during the neonatal period. In addition such
information is necessary for the formulation ©1982Americanlnstiluleo(Nu,ri,io„Receivedforpublic..™2«
OÕmilk Substitutes for kittens. December 1982
Although there is some information in the ' s"pp<>rtcdinp"rtbvN»«0"»1in*»ui«ofHealthresearchgrantHL-
18918 and HD-12547 from the National Institute of Child Health and Hu-
hterature witn regard to the major nutrients manDevelopment
1763
by guest on July 12, 2011jn.nutrition.orgDownloaded from
1764 KEEN ET AL.
changes in concentrations of the trace ele
ments iron, copper, zinc, and manganese, as
well as the major mineral elements calcium
and magnesium in the milk of domestic
short-hair cats. We have also determined the
concentrations of protein, carbohydrate and
fat in milk and the changes in these nutrients
during the course of lactation.
MATERIALS AND METHODS
Animals. Milk samples were obtained from
clinically healthy specific pathogen-free
domestic short-hair cats in the closed colony
at the University of California, Davis. Queens
were housed as a group in large (2.4 X 3.0
X 2.2 m) cages until the last trimester of preg
nancy when they were transferred to indi
vidual galvanized iron or stainless-steel cages
(0.9 X 0.9 X 0.9 m) and kept there until the
kittens were weaned. Queens were fed dry
cat food2 ad libitum during pregnancy and
lactation. During the third trimester and lac
tation, in addition to the dry food, approxi
mately 60 g of a canned food were offered
daily.
Milking procedure. Lactating cats (n = 26)
were given 5 lUof oxytocin (intramuscularly)
to stimulate milk flow and then milked by
gentle hand stripping of the teat. The free-
flowing milk was collected in disposable,
acid-washed 1 ml pipette tips (West Coast
Scientific, Oakland, CA). Collected milk was
stored frozen (—5°)in acid-washed plastic
vials until analyzed. Analyses were per
formed on single milk samples. About half
of the cats were milked only once. The other
cats were milked several times with at least
5 days separating each milking period. A to
tal of 106 samples were collected; in some
cases the volume collected was insufficient
for all the analyses. Data from cats milked
only once were grouped with those from cats
milked more than once. Although serial milk
ing may result in changes in milk composi
tion in the rat (2, 3), this was not found to
occur in the present study with cats. The day
of parturition was designated day 0 of lac
tation.
Analytical methods. Protein was deter
mined in milk samples (50 /il of a 1:30 di
lution) by a dye-binding method (Bio-Rad
Protein Assay Kit, Richmond, CA) (4). Car
bohydrate was determined by the orcinol-sul-
furic acid method described by Svennerholm
(5), with this technique, the sum of all pen-
toses and hexoses was estimated. Fat was de
termined by a calorimetrie method by using
the sulfuric acid-vanillin reaction described
by Zollner and Kirsch (6).
Atomic absorption spectrophotometry.
Milk samples (300 ¿tl)were wet ashed with
16 N nitric acid (2 ml of Ultrex grade, J. T.
Baker Co., San Francisco, CA), concentrated
by evaporation and diluted with distilled
deionized water (7). Calcium, magnesium,
iron, copper and zinc were determined by
flame atomic absorption spectrophotometry
(Perkin-Elmer Model 370, Perkin-Elmer
Corp., Norwalk, CT). For magnesium and
calcium analysis, the diluted ashed samples
were diluted further with 0.1% lanthanum
chloride in order to reduce matrix interfer
ence (8). Manganese was determined by
flameless atomic absorption (Models 157 and
555, Instrumentation Laboratories, Wilming
ton, MA). Standard addition of known con
centration of selected metal to the milk sam
ples indicated recoveries ranging between 98
and 102% for all elements.
Statistical methods. Changes in milk com
position that occurred throughout the 67 days
of the lactation were analyzed by linear
regression analysis (Statistical Package for the
Social Sciences-subprogram scattergram). For
this analysis cat was not included as a fixed
independent variable, because milk samples
from each animal were not available at all
time points. In addition to linear regression,
other modes of curve analysis were tested;
however, these approaches offered no con
sistent advantages. The regression equation
is shown, along with the r2 and P values, for
all analysis. To identify when changes oc
curred, data were grouped in 7-day periods
and analyzed by Student's i-test (BMDP/
Program P3D) (9). The first week of lactation
was further subdivided into days 0-2 and
days 3-7 to allow for the very low values
observed for some of the constituents during
the 0- to 2-day period. Comparisons were
"The cats received dry food (Crave, Kal Kan, Vernon, CA) containing:
84 ftg Fe; 6 fig Cu; 40 fig In; and 14 fig Mn (per gram dry weight) and
canned wet food (Kal Kan. Vernon, CA) containing: 318 fig Fe; 23 fig Cu;
64 fig Zn; and 18 fig Mn (per gram dry weight).
by guest on July 12, 2011jn.nutrition.orgDownloaded from
COMPOSITION OF CATS' MILK 1765
TABLE 1
Composition of cats' milk during lactation1
Nutrient
Days of lactation
0-2 3-7 8-14 15-21
Iron
Copper
Zinc
Manganese
Calcium
Magnesium
4.01 ±0.48 (6)
1.35 ±0.29 (5)
4.66 ±0.55 (6)
0.14 ±0.04 (7)
545 ±96 (6)
86 ±10 (6)
5.93 + 0.49 (21)
1.63 ±0.13 (21)
6.24 ±0.30- (21)
0.18 ±0.02' (21)
950 ±49b (20)
96 ±3 (21)
4.30 ±0.282b (17)
1.34 ±0.09 (17)
6.18 ±0.39 (17)
0.27 ±0.03 (17)
1,325 ±79b (15)
104 ±4 (17)
3.87 ±0.41
1.08 ±0.09
6.70 ±0.27
0.24 ±0.02
1,520 ±66
103 ±4
(14)
(14)
(14)
(14)
(13)
(13)
Protein
Carbohydrate
Fat
3.97 ±0.64 (5)
3.57 ±0.15 (6)
3.39 ±0.74 (5)
4.36 ±0.31 (17)
3.69 ±0.18 (16)
3.49 ±0.38 (15)
4.89 ±0.25 (15)
3.62 ±0.19 (15)
3.68 ±0.42 (15)
5.53 ±0.39 (14)
3.85 ±0.18 (14)
4.80 ±0.32' (14)
Nutrient 22-28
Days of lactation
29-35 36-42 43+
Iron
Copper
Zinc
Manganese
Calcium
Magnesium
4.14 ±0.58 (11)
0.93 ±0.12 (11)
7.04 ±0.40 (11)
0.30 ±0.03 (11)
1,725 ±57' (10)
105 ±7 (10)
Hg/ml
3.65 ±0.35 (11)
0.91 ±0.16 (11)
5.56 ±0.26b (11)
0.29 ±0.03 (11)
1,565 ±62 (10)
99 ±5 (10)
3.02 ±0.36
0.85 ±0.15
5.86 ±0.59
0.28 ±0.05
1,570±74
91 ±9
(11)
(11)
(11)
(11)
(11)
(11)
3.21 ±0.62
0.61 ±0.12
6.08 ±0.37
0.39 ±0.07
1,370 ±82
105 ±9
(7)
(7)
(7)
(7)
(5)
(5)
Protein
Carbohydrate
Fat
6.49 ±0.56 (11)
3.44 ±0.17 (11)
5.08 ±0.28 (11)
6.16 ±0.34 (11)
3.91 ±0.15 (11)
5.86 ±0.47 (11)
6.55 ±0.45 (10)
4.10 ±0.22 (9)
5.47 ±0.43 (10)
7.46 ±0.41 (6)
4.29 ±0.24 (6)
5.31 ±0.91 (6)
1Values are means ±SEM.Number of samples analyzed shown in parentheses,
preceding time period *(P :£0.05); b(P s 0.01). '•Significantly different from
then made between one time period and the
one immediately following.
RESULTS
Iron concentration in cats' milk decreased
significantly during the course of lactation
(Fe in fig/mi = 5.33 - 0.05 X days; r 2 = 0.20;
P ^ 0.001), from values of 5-6 Mg/ml during
the early part of lactation to about 3 ng/m\
in late lactation. An unusual finding was that
the colostrum during the first 2 days con
tained significantly less iron than did milk
in the day 2-7 period. Most of the decrease
in milk iron concentration occurred during
the second week of lactation (table 1).
Copper concentration decreased signifi
cantly during the course of lactation (Cu in
/tg/ml= 1.57-0.02 X days; r2 = 0.29; P
¿0.001), from 1.5-3.0 Mg/ml in early lac
tation to 0.2-1.0 fig/ml in late lactation. As
in the case of iron, the concentration of cop
per in the colostrum, collected on day 0 of
lactation, was lower than milk collected later
in lactation. Most of the decline in copper
concentration occurred during the weeks 2
and 3 of lactation (table 1).
The zinc concentration of milk did not
exhibit a strong developmental pattern, (Zn
in ¿ig/ml= 6.83 - 0.01 X days; r2 = 0.01;
P ^ 0.12). Zinc concentration, similar to that
for iron and copper, increased during the
by guest on July 12, 2011jn.nutrition.orgDownloaded from
1766 KEEN ET AL.
first two days of lactation (table 1). However,
a trend towards lower levels was observed in
late lactation with levels of approximately 6
Mg/ml at the end of lactation.
The concentration of manganese in milk
significantly increased during the course of
lactation (Mn in Mg/ml = 0.20 + 0.002
Xdays; r2 = 0.08; P <, 0.002) from about
0.10 Mg/ml on the first day of lactation to
more than 0.25 Mg/ml after the first week.
Most of the increase occured during the first
and second weeks of lactation (table 1).
The concentration of calcium in milk sig
nificantly increased during the course of lac
tation (Ca in Mg/ml = 203 + 31 X days; r2
= 0.36; P <, 0.001) from slightly above 500
Mg/ml in early lactation to more than 1500
Mg/ml in late lactation (table 1).
Magnesium concentration was not signif
icantly influenced by the progression of lac
tation (Mg in Mg/ml = 99 + 0.03 X days; r2
= 0.001; P ^ 0.40; the average concentration
was approximately 90 Mg/ml (table 1).
The protein concentration increased steadily
during lactation (protein percentage = 4.32
-I-0.06 X days; r2 = 0.30; F =s 0.001), from
less than 4% during early lactation to about
7% in late lactation (table 1).
Carbohydrate concentration increased
slightly during lactation from 3.5 to 4%, how
ever, there was considerable scatter in the
data (carbohydrate percentage = 3.59
+ 0.008 X days; r2 = 0.036; P <; 0.04)
(table 1).
Fat concentration increased significantly
during lactation (fat percentage = 3.20 + 0.67
X days; r2 = 0.33, F <; 0.001) from 1.4% to
about 5% in later lactation (table 1).
DISCUSSION
Iron
The iron concentration of cats' milk (ap
proximately 4/tg/ml) was found to be con
siderably higher than that of human milk,
which normally ranges from 0.2 to 0.5 Mg/
ml, and that of milk from most dairy animals,
which ranges between 0.2 and 0.3 Mg/ml
(10). Although it was lower than that re
ported for some marsupials, the rat, and the
dog (approximately 10 Mg/ml) (2, 11), the
iron concentration of cat milk is similar to
that reported for the rabbit (10). An unusual
finding in this study was that the colostrum
during the first 2 days contained considerably
less iron than did milk at the end of the first
week of lactation. This observation is in con
trast to reports for other species (10). Our
observation that the concentration of iron in
cats' milk is strongly influenced by the stage
of lactation, with values decreasing with
time, is similar to the findings for other spe
cies (2, 10, 11) including humans (12-15),
except for the first 2 days of lactation.
Like the dog, the rat, and some marsupials,
the cat is able to secrete milk in which the
concentration of iron may be several times
higher than that in plasma (normally about
0.5 Mg/ml). This finding suggests that trans
fer of iron into, or retention by, the mam
mary tissue of the cat occurs through mech
anisms different from those in species where
milk iron content is equal to or lower than
its plasma concentration. Physiological dif
ferences in mammary iron uptake between
species with iron-rich milk and those with
milk low in iron (such as the human) should
be elucidated to ascertain whether the cat is
a valid model for milk studies from which
correlations to humans may be drawn.
It is not known whether the iron in cat
milk is absorbed well by the kitten. The in
fants of other species with iron-rich milk,
such as the rat, can absorb almost 100% of
the iron ingested (10). Since anemia occurs
rarely in young kittens, it has been suggested
that the relatively slow growth rate of the
kitten compared to the young of other species
prevents depletion of its iron stores before
consumption of iron-rich solid food begins
(16). However, in comparison to the growth
rates of other small mammals, that of the
kitten is not unusually slow. Therefore, the
observation that anemia is found rarely in
the kitten may suggest that bioavailability of
the milk iron may be high.
Copper
The copper concentration of cats' milk,
ranging from approximately 2.0 Mg/ml in
early milk to 0.5 Mg/ml in late milk, is slightly
higher than that found for humans (0.3-0.6
Mg/ml colostrum, 0.2-0.3 Mg/ml mature milk)
and most dairy animals (0.1-0.5 Mg/ml) (17),
but similar to that of the dog (~2.0 Mg/ml)
by guest on July 12, 2011jn.nutrition.orgDownloaded from
COMPOSITION OF CATS' MILK 1767
(11), and lower than that of the rat which
has a relatively copper-rich milk (3-13 fig/
ml) (2). As with iron, the copper concentra
tion of cats' milk was very low in early co
lostrum as compared to milk 2-3 days post-
partum, which is in contrast to reports for
other species (17). It has been suggested that
colostrum is rich in copper because of a high
concentration of protein-bound copper, in
particular, immunoglobin-bound copper (18).
The cat may be an excellent model for study
ing this hypothesis by characterizing the pro
tein profile of milk from day 0 to day 5 of
lactation.
Except for the first 2 days of lactation, the
levels of copper decreased throughout lac
tation. This type of developmental pattern
is similar to that observed for most species
(10), although in the dog, concentrations of
copper in milk were not influenced by the
stage of lactation (11). Further, we have ob
served that liver copper concentration does
not decline in the growing cat (Keen, C. L.,
unpublished data). This may indicate that the
copper from cats' milk is highly bioavailable.
Zinc
The concentration of zinc in cats' milk
(~6 /ig/ml) is similar to that reported for
most species. However, in contrast to other
species studied, in the cat the milk concen
tration of zinc was not influenced by the stage
of lactation. This may in part be explained
by the fact that cats' milk contains a com
paratively high proportion of zinc associated
to a low-molecular-weight compound (17).
The proportion of zinc in milk associated
with this fraction in humans does not vary
greatly during lactation (17).
Manganese
In contrast to several other species (10)
cats' milk manganese increases during early
lactation. The concentration of manganese
in cats' milk is over 10 times higher than that
reported in human milk, but is similar to that
of the rat, dog, and some ruminants (2, 11,
17). Little is known at this time regarding
bioavailability or importance of milk man
ganese. The recent report by Dupont and co-
workers (19), which suggests the occurrence
of manganese deficiency in young children
with convulsive disorders, demonstrates the
need for further studies on milk manganese
and its nutritional role.
Calcium
Calcium concentrations of cats' milk are
similar to those reported for several species.
It was strongly influenced by the stage of
lactation, increasing over 200% during the
first 3 weeks. The pattern of calcium con
centration, increasing with lactation time,
was similar to that of protein concentration.
Since one of the major proteins of feline milk
is casein (20), well known for its calcium-
binding capacity, the good correlation be
tween calcium and protein concentration is
expected.
Magnesium
The concentration of magnesium in cats'
milk was similar to that reported for other
species (2,11), and was not influenced by the
stage of lactation. This observation is similar
to reports concerning dog milk and human
milk (11,14), but in contrast to those for cows
(21) and rats (2), in which the values de
creased with lactation time. Unlike calcium,
milk magnesium concentration was not sig
nificantly correlated to milk protein concen
tration. This is in accordance with findings
in human milk, where virtually all magne
sium is present in a low-molecular-weight
fraction and not bound to proteins (22).
Protein
The pattern for protein concentration in
cats' milk during lactation indicated that pro
tein increases from 2 to 4% in the first part
of lactation to about 6-8% by mid- to late
lactation. This pattern contrasts that of milk
proteins of humans (23) and cows (24), in
which the concentration decreases rapidly
during the first part of lactation. An increase
in milk protein concentration with lactation
time has been reported for the rat (2) and
dog (11).
The observation that the protein concen
tration of cats' milk is similar to that of rat
and dog was somewhat surprising. It is be
lieved that the cat has a requirement for pro-
by guest on July 12, 2011jn.nutrition.orgDownloaded from
1768 KEEN ET AL.
tein higher than that of most mammalian
species, especially considering its relative
growth rate. This relatively high requirement
is probably the result of an inability of the
cat to adapt from an ancestral high "carni
vore" protein diet to a low "noncarnivore"
protein diet. It has been shown that the ac
tivity of the urea cycle enzymes in cat liver
are nonadaptive (25). Thus, one might pre
dict that the protein content of cat milk
should be high relative to most species. By
calculation, the protein of cat milk at mid-
lactation contributes approximately 28% of
the total energy. This value is higher than
the determined value of the minimal protein
requirement for the growth of kittens re
ceiving an "ideal" protein.3 If cat milk does
not exceed the protein requirement of pre-
weaning kittens, the protein requirement of
preweaning kittens appears to be higher than
that of postweaning kittens. In the adult
stage, maintenance protein requirement has
been calculated to be about 12% (26). Other
species such as the rat and dog have a higher
protein requirement during the suckling pe
riod than in the postsuckling period. Since
the cat has a high requirement for the sulfur
containing amino acids, arginine and taurine,
the amino acids provided by cat milk may
be different from those of most species.
Carbohydrate
Values obtained in this study for milk car
bohydrate (3-5%) are similar to those re
ported for most species (2, 11). No strong
developmental pattern for milk carbohydrate
concentration was found, although there was
a trend for values to increase with lactation
time. A similar weak pattern was found for
the dog (11) and the rat (2).
Fat
An important constituent in cat milk quan
titatively is fat, since it supplies most of the
kitten's energy. The observation that fat con
centration increases during lactation is sim
ilar to that found for the cow (17) and the
dog (11), but is in contrast to reports for hu
man (27) and rat milk (2) in which fat con
centrations are not significantly influenced
by lactation stage.
In conclusion, the composition of cats' milk
was found to vary considerably with the stage
of lactation. The concentrations of iron, cop
per, manganese, calcium, protein, carbohy
drate and fat showed patterns that were in
fluenced by the stage of lactation, whereas
concentrations of zinc and magnesium, were
not significantly affected. These data show
that the nutrient intake of the suckling kitten
changes markedly during the early neonatal
period. Such changes should be taken into
account when evaluating the trace element
status of the growing kitten. Furthermore,
lactational patterns should be considered
when evaluating the cat as a model for trace
element nutrition in humans with specific
attention given to similarities and differ
ences.
LITERATURE CITED
1. Kataoka, K., Nakae, T. & Imamura, T. (1972)
Comparative studies on the milk constituents of var
ious mammals in Japan. V. Comparison in mineral
composition of the milk from various mammals. Jpn.
J. Dairy Sci. 21, A142-A156.
2. Keen, C. L., Lonnerdal, B., Clegg, M. & Hurley,
L. S. (1981) Developmental changes in composi
tion of rat milk: trace elements, minerals, protein,
carbohydrate and fat. J. Nutr. Ill, 226-236.
3. Keen, C. L., Lonnerdal, B., Sloan, M. V. & Hurley,
L. S. (1980) Effects of milking procedure on rat
milk composition. Physiol. Behav. 24, 613-615.
4. Bradford, M. M. (1976) A rapid and sensitive method
for the quantitation of microgram quantities of pro
tein utilizing the principle of protein-dye binding.
Anal. Biochem. 72, 248-254.
5. Svennerholm, L. (1956) The quantitative esti
mation of cerebrosides in nervous tissue. J. Neuro-
chem. 1, 42-53.
6. Zollner, N. & Kirsch, K. (1962) Ãœberdie quanti
tative Bestimmung von Lipoiden (Mikromethode)
Mittels der vielen naturlichem Lipoiden (allen be
kannten Plasmolipoiden) gemeinsamen Sulfophos-
phovanillin-Reaktion. Z. Gesamte Exp. Med. Õ35,
545-561.
7. Clegg, M. S., Keen, C. L., Lonnerdal, B. & Hurley,
L. S. (1981) Influence of ashing techniques on the
analysis of trace elements in animal tissue. I. Wet
ashing. Biol. Trace Element Res. 3, 107-115.
8. Christian, G. D. & Feldman, F. J. (1970) Atomic
Absorption Spectroscopy: Applications in Agricul
ture, Biology, and Medicine, Wiley-Interscience,
New York.
9. Dixon, W. J. & Brown, M. B. (1979) BMDP
Biomedicai Computer Programs P-Series, chapter
9, University of California Press, Berkeley, CA.
'We have found (unpublished. Smalley, K., Rogers, Q R. and Morris,
J. C.) that the protein requirement ("ideal protein") of the growing kitten
is 16.0)6of calories.
by guest on July 12, 2011jn.nutrition.orgDownloaded from
COMPOSITION OF CATS' MILK 1769
10. Lonnerdal, B., Keen, C. L. & Hurley, L. S. (1981)
Iron, copper, zinc and manganese in milk. Annu.
Rev. Nutr. 1, 149-174.
11. Lonnerdal, B., Keen, C. L., Hurley, L. S. & Fisher,
G. L. (1981) Developmental changes in the com
position of Beagle dog milk. Am. J. Vet. Res. 42(4),
662-666.
12. Khurana, V., Agarwal, K. N. & Gupta, S. (1970)
Iron content of breast milk. Indian Pediatr. 7, 659-
661.
13. Picciano, M. & Guthrie, H. (1976) Copper, iron
and zinc contents of mature human milk. Am. J.
Clin. Nutr. 29, 242-254.
14. Sûmes,M. A., Vuori, E. & Kiutunen, P. (1979)
Breast milk iron—adeclining concentration during
the course of lactation. Acta Paediatr. Scand. 68, 29-
31.
15. Vaughan, L. A., Weber, C. W. & Kemberling, S. R.
(1979) Longitudinal changes in the mineral content
of human milk. Am. J. Clin. Nutr. 32, 2301-2306.
16. Loeb, W. F. (1975) Blood and blood forming or
gans. In: Feline Medicine and Surgery, 2nd ed.
(Catcott, E. J., ed.), chapt. 11, Am. Vet. Publications,
Inc., Santa Barbara, CA.
17. Lonnerdal, B., Keen, C. L. & Hurley, L. S. (1981)
Trace elements in milk from various species. In:
Trace Element Metabolism in Man and Animals
(TEMA-4) (Howell, J. McC., Gawthorne, J. M., &
White, C. L., eds.), pp. 249-252, Griffin Press Ltd,
Netly, South Australia.
18. Prins, H. W. & Van den Hamer, C. J. A. (1978)
Cu-content of the liver of young mice in relation to
a defect in the Cu-metabolism. In: Trace Element
Metabolism in Man and Animals-3., (Kirchgessner,
M., éd.),pp. 397-400, Technischen Universität
München,Freising-Weihenstephan, West Germany.
19. Dupont, C., Harpur, E. R., Skoryna, S. C. & Tanaka,
Y. (1977) Blood manganese levels in relation to
convulsive disorders in children. Clin. Biochem. 10,
11.
20. Kataoka, K. & Nakaeg, T. (1972) Comparative
studies on the milk constituents of various mammals
in Japan. III. Comparison of composition of milk
proteins from non-ruminants. Jpn. J. Dairy Sci. 21,
A27-A34.
21. Linden, G. & Maraval, B. (1979) Colostrum de
vache: composition minerale et activitéde la phos-
phatase alcaline. Ann. Biol. Anim. Biochem. Bio-
phys. J9(2A), 337-341.
22. Lonnerdal, B. & Fransson, G.-B. (1981) Distribu
tion of copper, zinc, calcium and magnesium in hu
man milk. Proceedings of XII International Congress
of Nutrition (in press).
23. Lonnerdal, B., Forsum, E. & Hambraeus, L. (1976)
A longitudinal study of the protein, nitrogen, and
lactose contents of human milk from Swedish well-
nourished mothers. Am. J. Clin. Nutr. 29, 1127-
1133.
24. Parrish, D. B., Wise, G. H., Hughes, J. S. & Atkeson,
F. W. (1950) Properties of the colostrum of the
dairy cow. V. Yield, specific gravity and concentra
tions of total solids and its various components of
colostrum and early milk. J. Dairy Sci. 33, 457-465.
25. Rogers, Q. R., Morris, J. G. & Freedland, R. A.
(1977) Lack of hepatic enzymatic adaptation to low
and high levels of dietary protein in the adult cat.
Enzyme 22, 348-356.
26. Burger, I. H., Biaza, S. E. & Kendall, P. T. (1981)
The protein requirement of adult cats. Proc. Nutr.
Soc. 41, 361A.
27. Hytten, F. E. (1954) Clinical and chemical studies
in human lactation: II. Variation in major constitu
ents during a feeding. Br. Med. J. 1, 175-182.
by guest on July 12, 2011jn.nutrition.orgDownloaded from
