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Lactation in the Dog: Milk Composition and Intake by Puppies

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The composition and intake of milk by mother-reared puppies was studied to compare protein and energy intakes of puppies with estimated requirements. Milk samples were obtained from five beagle bitches over the period of 7-37 days postpartum. Dog milk contained on average 22.7% dry matter, 9.47% fat, 7.53% protein, 3.81% sugar and 146 kcal gross energy per 100 g. Protein comprised 31% of milk energy. Nonprotein nitrogen averaged 0.054%, equivalent to 4.4% of total nitrogen. Milk intakes of puppies in the five litters were estimated from water kinetics following administration of deuterium oxide (D2O). D2O dilution indicated that body water comprised 72-73% of puppy body weight, and fractional turnover rate of body water averaged 0.15-0.17% per day in weeks 3 and 4 postpartum. Milk intakes were calculated as 160 +/- 5.4 g (mean +/- SEM) at 19 days and 175 +/- 5.3 g at 26 days, equivalent to 17.0 and 14.6% of body weight, respectively. Daily milk yields of the bitches averaged 964 g at 19 days and 1054 g at 26 days. Dry matter intakes of the puppies were equivalent to 3.9 and 3.3% of body weight at 19 and 26 days, respectively. Gross energy intakes averaged 223-224 kcal/ kg0 .75 per day, and protein intakes averaged 0.33-0.36 g per gram body weight gain at these ages. Estimates of the energy requirements of young puppies by the National Research Council appear to be too high.
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Lactation in the Dog: Milk Composition and
Intake by Puppies
OLAV T. OFTEDAL1
Division of Nutritional Sciences, Cornell University,
Ithaca, NY 14853
ABSTRACT The composition and intake of milk by mother-reared puppies was
studied to compare protein and energy intakes of puppies with estimated require
ments. Milk samples were obtained from five beagle bitches over the period of 7-37
days postpartum. Dog milk contained on average 22.7% dry matter, 9.47% fat, 7.53%
protein, 3.81% sugar and 146 kcal gross energy per 100 g. Protein comprised 31% of
milk energy. Nonprotein nitrogen averaged 0.054%, equivalent to 4.4% of total
nitrogen. Milk intakes of puppies in the five litters were estimated from water kinetics
following administration of deuterium oxide (D2O). D2O dilution indicated that body
water comprised 72-73% of puppy body weight, and fractional turnover rate of body
water averaged 0.15-0.17% per day in weeks 3 and 4 postpartum. Milk intakes were
calculated as 160 ±5.4 g (mean ±SEM) at 19 days and 175 ±5.3 g at 26 days,
equivalent to 17.0 and 14.6% of body weight, respectively. Daily milk yields of the
bitches averaged 964 g at 19 days and 1054 g at 26 days. Dry matter intakes of the
puppies were equivalent to 3.9 and 3.3% of body weight at 19 and 26 days, respec
tively. Gross energy intakes averaged 223-224 kcal/kg"" per day, and protein intakes
averaged 0.33-0.36 g per gram body weight gain at these ages. Estimates of the energy
requirements of young puppies by the National Research Council appear to be too
high. J. Nutr. 114: 803-812, 1984.
INDEXING KEY WORDS dogs •lactation •milk composition •milk
yield •water kinetics
Milk composition and yield vary greatly age or less are reported to consume the
among diverse mammalian species (1-3). equivalent of 10-14% of body weight per day
Estimation of the nutrient requirements of (7, 9). The effects of maternal nutrition (9,
both mother and suckling young requires 10), maternal size (2), breed (6), and litter size
quantitative information on lactation per- and mass on lactation performance in dogs
formance. Dogs are known to produce a need clarification.
rather concentrated milk containing 21-26% The following study was undertaken to
total solids, 8-12% fat and 7-10% protein measure milk composition and milk yield at
(4-7), although lower levelsof fat and protein peak lactation in well-nourished dogs of the
have recently been reported (8). Little in- beagle breed. This study is part of a larger
formation is available on milk yields in dogs, project in which lactation performance is
Several litters of various breeds have been compared among several species, and nutri-
studied by weighing puppies before and after ent intakes of suckling young are related to
suckling (6, 7). A German shepherd was esti- body size, growth rates and estimated re-
mated to produce 1.7 kg milk per day at the quirements (3, 11). Milk production was
lactation peak at 3 weeks postpartum, where-
aS bitches Of Smaller breeds produced leSS ©1984 American Institute of Nutrition. Received for publication
milk but were only studied in the first 9 days 27,]une1983M
,„. ^ ... , . J - Current address: Department of Zoological Research, National
(b). bUCkling pUppieS 4 WeekS Or Zoological Park, Smithsonian Institution, Washington, DC 20008.
803
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804 OFTEDAL
measured from the dilution and turnover of
deuterium oxide (D2O) administered to
puppies. Hydrogen isotopes have been
shown to yield valid estimates of milk
production if corrections are made for
changes in body water pool size and for
isotope recycling via maternal milk (11-15).
Peak lactation was assumed to occur in week
3 or 4 postpartum since puppies do not
initiate feeding on semisolid food until the
emergence of deciduous dentition at 21 to 35
days postpartum (16-18). Milk alone will
support normal growth up to 4 weeks post
partum; thereafter, withholding of supple
mental food may result in a reduced growth
rate (19).
MATERIALS AND METHODS
Experimental animals. Five bitches \\ere
studied at the long-established beagle re
search colony at Cornell University (20).
The bitches were 1.5-3.7 years of age, had
postpartum weights of 9.3-15.2 kg (mean
= 12.7 kg) and were producing their first or
second litters. One week prior to the ex
pected parturition date each dog was
removed from the main colony to an isolated
whelping room. They were individually
housed in 1.2- x 1.1-m cages (horizontal
dimensions) with 0.7- x 0.7-m heated
whelping boards, and were fed a commer
cial dry dog food (Wayne Dry Dog Food,
Allied Mills, Inc., Chicago, IL) containing
about 26% crude protein, 9% fat, 4% crude
fiber and 2.75 kcal metabolizable energy
(ME) per gram.2 Water was provided ad
libitum in elevated stainless-steel bowls that
were too high for the puppies to drink from.
At birth litter size ranged from 5 to 10 pup
pies; 5 to 7 puppies per litter survived
beyond 1 week postpartum. The puppies
were first offered supplemental feed [dry
dog food (Wayne Dry Dog Food) soaked in
evaporated milk and water] at 29-30 days
postpartum. Puppies were weighed to the
nearest gram at least three times per week
over the course of the study.
Milk sampling and analysis. Milk samples
were collected at weekly intervals from 7-37
days postpartum. Additional samples were
also taken during weeks 2 and 5 post
partum. Bitches were removed from their
litters for 2-3 hours prior to milking. Oxy-
tocin (5 IU) was administered by intramus
cular injection, and one or two teats evacu
ated as completely as possible by gentle
manual expression. An average of 21 ml
( ±6.3 SD) was obtained in 10-15 minutes.
Samples were frozen in sealed vials until
analyzed.
Milk samples were thawed quickly, ho
mogenized in a Potter-Elvehjem tissue
grinder and subsampled. The weekly sam
ples were assayed in duplicate for major
constituents. Total solids were determined
by oven drying, total nitrogen (TN) and
nonprotein nitrogen (NPN) by a Kjeldahl
procedure, fat by the Roese-Gottlieb method
(21) and sugar by the phenol-sulfuric acid
colorimetrie method, as previously described
(21). Sample size did not permit NPN deter
mination on eight samples. In such cases an
additional sample collected from the same
bitch within 2 to 3 days was substituted.
Both TN and NPN were measured on these
additional samples. Protein was calculated
as 6.38 x (TPN - NPN). Gross energy
was estimated from an equation developed
by Perrin (22), as previously presented (21).
Milk intake estimation procedure. Milk
intake was estimated from water kinetics of
25 puppies in the five litters. D2O (99.8%
purity) was administered by stomach tube
to puppies at 15-16 days and 22-23 days
postpartum at a rate of 2.3 g/kg body
weight. One young in each litter was not
given D2O so that correction could be made
for isotope recycling. Two hours were al
lowed for isotope equilibration prior to
collection of about 2 ml of blood by jugular
puncture; in young puppies hydrogen iso
topes equilibrate in 1.5 hours (23). Each
puppy was bled at 2- to 3-day intervals such
that four samples were collected during
each weekly study period for determination
of water turnover. The second isotope
administration immediately followed the
final bleeding of the preceding period such
that residual isotope levels could be mea
sured. Blood water was isolated by heat
distillation and assayed for deuterium con
centration by infrared spectrophotometry
(24) using matched barium fluoride cells
(0.11-mm path length) in a double beam
"Nutritional information supplied by manufacturer.
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LACTATION IN THE DOG 805
grating infrared spectrophotometer (Model
521, Perkin-Elmer Corp., Norwalk, CT).
Assayed deuterium levels were corrected
for body weight changes in computations of
fractional turnover rate (k) and body water
fraction (F)(ll). Isotope recycling via mater
nal ingestion of the excreta of suckling
young, followed by transfer of isotope in
milk water from mother to young (12),
necessitated an additional correction. The
accumulation of deuterium in an unin-
jected, control puppy in each litter was
monitored. On the assumption that these
levels are representative of recycled isotope
in littermates, the deuterium levels in con
trol puppies were subtracted from the
deuterium levels of their littermates prior to
regression of corrected log D2O concentra
tion against time after administration.
Daily water loss, water gain and water
intake were computed as previously de
scribed (21). The proportions of milk
constituents catabolized to produce meta
bolic water were estimated by iterative
calculations detailed elsewhere (11). Sta
tistical analyses were performed using
programs of the Statistical Package for the
Social Sciences (SPSS) on a Honeywell
computer at the Smithsonian Institution.
Mean values are presented as mean ±SEM
unless otherwise indicated.
RESULTS
Milk composition. Over the period of 7 to
37 days postpartum (table 1) there were no
significant differences in total solids, fat,
protein or gross energy content among
sampling times [P > 0.05, analysis of vari
ance (ANOVA)]. Sugar content did differ
among sampling times (P < 0.05, ANOVA),
the mean value rising from 3.47% at 7 to 9
days postpartum to 4.13% at 29 to 30 days
postpartum. The mean values for all sam
pling times were: 22.7 ±0.41% total solids,
9.47 ±0.386% fat, 7.53 ±0.123% protein,
3.81 ±0.079% sugar and 146 ±3.6 kcal
gross energy per 100 g. If converted to a dry
matter basis dog milk was found to contain
41.4 ±0.87% fat, 33.4 ±0.60% protein,
17.0 ±0.049% sugar and 641 ±3.9 kcal/
100 g dry matter. Fat, protein and sugar
provided 58.7 ±0.86%, 30.5 ±0.66% and
10.5 ±0.33% of total gross energy, respec
tively. There were no significant differences
in milk composition among the five bitches,
whether compared on a whole-milk, dry
matter or gross energy basis (P > 0.05,
ANOVA). NPN ranged from 0.045 to 0.068%
(mean = 0.054 ±0.0012%), equivalent to
3.4-5.2% of total nitrogen. NPN did not
differ significantly among bitches or sam
pling times (P > 0.05, ANOVA).
Water and milk intakes. Water and milk
intakes were calculated for the midpoints of
each study period, i.e., for 19 and 26 days
postpartum (table 2). Growth rates and esti
mated body weights at these ages derive
from regressions of puppy weight on post
natal age These regressions were highly
linear (mean r2 = 0.990). Regressions of the
logarithm of corrected deuterium concen
tration on time after isotope administration
were also highly linear (mean r2 = 0.996).
Deuterium content in body water of unin-
jected control puppies reached levels equiva
lent to 11.5 ±0.45% and 10.6 ±0.30% of
the levels in injected littermates by the final
TABLE 1
Composition of dog milk1'*
Time of milk sampling, days postpartum
Constituent3Total
solids,%Fat,
%Protein,
%Sugar,
%Gross
energy,kcal/100
g7-923.5
±1.31*10.90
±1.370*7.17
±0.092'3.47
±0.087*155
±12.3*15-1622.9
±1.41'9.67
±1.171*7.59
±0.275*3.61
±0.111*b147
±11.9*22-2322.1
±0.51*8.73
±0.230*7.72
±0.390*4.04
±Q.nS**141
±3.4*29-3022.3
±0.64*8.89
±0.410*7.49
±0.303*4.13
±0.149C142
±4.5*36-3722.6
±0.72*9.16
±0.482*7.70
±0.281*3.81
±o.ise'1*144
±5.0*Total22.7
±0.419.47
±0.3867.53
±0.1233.81
±0.079146
±3.6
'Mean ±SEM;n = 5 for each time period; n - 25 for total. "Means with the same superscript in a row do not differ by
more than the shortest significant range at the 0.05 significance level (Duncan's multiple-range test). 'Percentage values
represent gram per 100 g.
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806 OFTEDAL
blood sampling in the first and second study
periods, respectively. Correction for isotope
recycling was therefore warranted.
Fractional turnover rate of body water (k)
declined from 0.168 ±0.0036 per day for
the first study period to 0.152 ±0.0034 per
day for the second (P < 0.001, paired i-test).
By contrast body water fraction (F) did not
differ significantly (P > 0.05, paired f-test)
between the two periods (table 2). Calcu
lated water losses, water gains and water
intakes at 19 and 26 days postpartum are
presented in table 2. Water intake was
equivalent to 15.1 and 13.9% of body weight
at 19 and 26 days, respectively.
Water intake derives from both preformed
milk water and metabolic water from the
catabolism of milk solids. Body composition
data presented by Sheng and Huggins (25)
indicate weight gain comprises 12% protein
and 13% fat in the period of 16-33 days
postpartum. On the basis of these values,
combined with milk composition, growth
rate and water intake data, one can calcu
late that the amounts of fat and protein
catabolized are equivalent to 69 and 72% of
ingested fat and 63 and 67% of ingested
protein at 19 and 26 days, respectively. It
was assumed that 100% of ingested sugar
was catabolj^ed. Ingestion of 100 g milk will
then yield 77.3 g preformed and 11.7 g meta
bolic water at 19 days and 77.3 g preformed
and 11.7 g metabolic water at 26 days.
Milk intake was estimated as water intake
x 1.129at 19days and water intake x 1.124
at 26 days (table 3). Individual milk intakes
of puppies ranged from 126 to 239 g/day at
19 days and from 134 to 229 g/day at 26 days.
TABLE 2
Body water turnover in suckling puppies
Time after parturition, day
Measure 19 26
Body wt, g
Wt gain, g/day
Fractional
turnover, (k)
Wt fraction,1 (F)
Water loss, g/day
Water gain, g/day
Water intake, g/day
942±25.4
36.8±1.28 1199±33.3
36.8±1.28
0.168±0.00360.152±0.0034
0.726±0.00680.716±0.0084
115±4.2 130±4.1
26.6±0.80 26.1•0.68
142±4.8 156±4.7
'Grams body water per gram body weight.
Milk intakes of puppies were compared
among litters and between the two post
natal ages by two-way ANOVA. Whether
expressed as a daily amount, as a percentage
of body weight per day, or per gram body
weight gain, mükintake was significantly
influenced by both litter and age effects
(table 3). Although the absolute amount of
milk consumed per day at 26 days (175
±5.3 g) was greater (P < 0.01) than that at
19 days (160 ±5.4 g), this amount repre
sented a smaller percentage of body weight
(14.6% at 26 days vs. 17.0% at 19 days, P
< 0.001). Since the same estimate of growth
rate was used for both age categories, milk
intake per gram body weight gain was of
course greater at 26 days (table 3). The
mean milk intakes in four litters were rela
tively similar (147-156 g/day at 19 days;
159-178 g/day at 26 days), but the puppies in
the litter of bitch BR 82 consumed appre
ciably more milk on average (203 g/day at
19 days and 221 g/day at 26 days). Puppies
in the larger litters tended to be smaller and
grow at a reduced rate but did not appear to
ingest substantially less milk than the pup
pies in smaller litters at these ages (table 3).
Total milk output of lactating bitches
(milk intake per puppy x litter size) was
estimated as 964 ±57.6 g/day (n = 5) at 19
days and 1054 ±57.7 g/day at 26 days
(table 3). These estimates are not signifi
cantly different (P > 0.05, paired i-test).
These yields correspond to 7.6% of maternal
weight or 143 g/kg°75at 19 days and 8.3%
or 157 g/kg°7Sat 26 days.
Nutrient intakes. By combining mean
milk composition (table 1) and mean milk
intake (table 3) data, the intake of various
constituents can be calculated. At 19 days
suckling puppies ingested 36.3 g dry matter
(3.86% of body weight), 15.2 g fat, 12.0 g
protein, 6.1 g sugar and 234 kcal (224
kcal/kg0 7S).At 26 days intakes were 39.7 g
dry matter (3.31% of body weight), 16.6 g
fat, 13.2 g protein, 6.7 g sugar and 256 kcal
(223 kcal/kg075). For each gram of body
weight gain, puppies ingested 0.33 g protein
and 6.4 kcal at 19 days and 0.36 g protein
and 7.0 kcal at 26 days.
DISCUSSION
Milk composition. Milk collected from
beagle bitches contained on average 22.7%
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LACTATION IN THE DOG 807
TABLE 3
Milk intakes of suckling puppies'
BR82
BR50
CA46
CD 18
CA45
All litters
BR82
BR50
CA46
CD 18
CA45
All litters
5
5
6
7
7
Milk intake of puppies
Bitch
designationLitter sizeDaily intakeAs ÕÕwtPer gram
wt gainMilk output
of bitch
203152154156147160
±5.221166178165159175
±519
dayspostpartum18.714.816.717.317.34
17.0 ±0.3026
ilnu\postpartum15.712.815.114.414.83
14.6 ±0.22
4.51
4.02
4.13
4.54
4.55
4.37 ±0.074
4.91
4.39
4.80
4.82
4.92
4.79 ±0.071
Analysis of variance
1015
760
924
1092
1029
964 ±57.6
1105
830
1068
1155
1113
1054 ±57.7
Litter effect
F(4,44)
Age effect
F(l,44)P
< 0.001
P < 0.01P
< 0.001
P < 0.001P
< 0.001
P < 0.001—
'Milk intakes are litter means. Values after ± are SEM.
total solids, 9.5% fat, 7.5% protein and
3.8% sugar. Mean values from prior studies
on dog milk are tabulated for comparison
(table 4). This list includes 19th century
results of questionable analytical accuracy
as well as studies involving only a few sam
ples from one or two dogs. Samples collected
very early or late in lactation have been
excluded as not representative of established
lactation. Despite variation in sampling and
analytical procedures, most reports fall
within the ranges of 21-26% total solids,
8-12% fat, 7-10% protein and 3-4% sugar
(table 4). The results reported herein are
consistent with these values. By contrast the
recent data of Lönnerdaland colleagues (8)
indicate much lower fat (4.8%) and protein
(5.2%) levels in beagle milk collected 11-40
days postpartum. This discrepancy may
stem from inappropriate application of
rapid spectrophotometric methods. Color
development in the sulfuric acid-phosphoric
acid-vanillin reaction employed in the
determination of fat depends on the degree
of unsaturation of the lipids (34). Binding of
Coomassie brilliant blue G250 dye to pro
tein is likewise a function of the amino acid
composition of the protein (35, 36). These
methods are valid only if standardized to the
particular mix of lipid and protein constitu
ents found in dog milk. It appears that this
was not done
The variation among the remaining
studies may be a function of sampling or
analytical bias or may represent real differ
ences among dogs. Dog breeds vary tre
mendously in body size and conformation,
but no correlation to the gross composition
of milk could be determined by Russe (6)
who studied breeds ranging in size from
dachshunds to Saint Bernards. Beagle milk
collected by Luick and colleagues (5) con
tained more total solids, fat and protein, but
less sugar (table 4) than was found in the
present study. By contrast the recent data of
Mundt and colleagues (7) are very similar to
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808 OFTEDAL
TABLE 4
Published data on the composition of dog milk at midlactation
Source Females
milked Days after
birth No. of
samples Total
solids Fat Protein Sugar
Ssubotin 1866(26)Tolmatscheff
1867(27)Abderhalden
1898(28)Abderhalden
1899(29)Dijkstra
1910(30)Grimmer
1915(31)Daggs
1931(10)Deniges
1935(32)Anderson
et al. 1940(4)Luick
et al. 1960(5)Russe
1961(6)Lauer
et al. 1969(33)Mundt
et al. 1981(7)Lönnerdal
et al. 1981(8)Present
study312111321372716512-38?355-1110-146-205-2621-35?18-3015-365-35307-2811-407-3712'2913222'8122-4'3032-63'218-28'62-71'2520.8————20.823.924.222.626.022.026.422.0—22.78.811.811.511.66.58.512.410.68.312.311.112.39.74.89.58.8s8.227.027.3s6.837.2'8.039.337.559.8*6.958.2*7.3"5.2"7.5'2.73.23.33.12.6—3.22.73.73.33.32.93.64.53.8
'Early and/or late lactation samples excluded. 2Protein determined by precipitation and weighing. 'Assay
method not specified. 4Protein calculated as protein nitrogen (Kjeldahl) x 6.38. 'Protein calculated as total
nitrogen (Kjeldahl) x 6.38. 'Protein measured by dye-binding procedure.
the present results although four breeds as
well as mongrels were included. Breed dif
ferences in the composition of dog milk
must be minor if they exist at all.
An elevation in total solids and protein at
both the beginning and the end of lactation
has been noted in prior reports (4, 6, 31). In
the present study there were no substantial
changes in milk composition from 7 to 37
days postpartum, a week after supplemental
feeding of puppies commenced. Marked
compositional changes are apparently asso
ciated with mammary involution at about
39—49days (4, 6). Weaning is of course
influenced by feeding and management
practices, and perhaps by breed as well (6).
Lonnerdal et al. (8) have reported a rise in
fat and protein contents of beagle milk from
0 to 40 days, and a subsequent decline in fat
content. These trends are at odds with other
findings and could reflect sensitivity of the
spectrophotometric assay procedures to
qualitative as well as quantitative changes
in milk constituents. Canine caseins and
whey proteins certainly differ in amino acid
composition (37) such that varying propor
tions during lactation (6) will affect protein
content as measured by dye-binding.
The NPN content of dog milk averaged
0.054%. The data of Grimmer (31) and
Russe (6) indicate mean NPN values of 0.068
and 0.112%, respectively. In the present
study NPN accounted for only 4.4% of total
nitrogen, as compared to 5.7 (31) and 9.3%
(6). Protein estimates based on total nitro
gen (e.g., see refs. 4, 5, 7, 33) will over
estimate true protein by an amount equal to
NPN x 6.38, i.e., by about 0.3 to 0.7
percentage points.
In 100 g milk, 1.88 ±0.062 g of solids
was not accounted for by the summation of
fat, protein and sugar. Part of the residual is
due to ash and part to NPN constituents. If
published data on the ash content of dog
milk in the period of 5 to 35 days postpartum
(4, 7, 10, 28, 30-33) are considered collec
tively, a mean ash content of 1.15% can be
calculated (n = 57). Assuming the NPN
constituents of dog milk to be similar in
proportion to those of cow's milk (38), NPN
X 5.34 = 0.29% gives an approximation of
the combined weight of NPN constituents
(11). The remaining 0.44 g ( = 1.88 - 1.15
- 0.29) represents minor organic and
inorganic compounds not included in the
various analytical fractions (38) as well as
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LACTATION IN THE DOG 809
analytical error. On this basis it would
appear that any such error was small.
Water and milk intakes. Suckling beagle
puppies were estimated to consume 142 g
water, equivalent to 160 g milk, at 19 days
postpartum, and 156 g water, equivalent to
175 g milk, at 26 days postpartum (table 2).
These values are only as accurate as the
estimates of body water fraction (F) and
water turnover rate (fc)on which the calcu
lations are based. Isotope dilution proce
dures have been reported by Sheng and
Huggins (23, 25) to overestimate body water
content in growing beagles when compared
to values obtained by direct dessication.
Dilution of tritiated water indicated body
water percentages of 75-92% at 8-21 days
(23), whereas direct dessication values were
65-74% at the same sampling times (25).
These results have been contested with al
legations that the analytical procedures
must have been in error (39). Neither the
mean values obtained in the present study
(72-73%) nor the values reported by Romsos
and colleagues (9) for 4-week-old puppies
administered tritiated water (74-76%) ap
pear to be greatly in excess of expected
values. Widdowson (40) reported that
3-week-old puppies contain 68% water. It
appears that isotope dilution may over
estimate body water in puppies by a few
percentage points but not to the degree
reported by Sheng and Huggins (23).
The decline in water turnover rate from
0.168 in the first week of study to 0.152 in
the second may reflect in part that puppies
were not allowed supplemental water or
feed prior to 29 to 30 days postpartum.
Maternal régurgitationof feed to puppies
was not observed; disgorging of food has
been reported as early as 21-24 days post
partum by Martins (41). Any ingestion of
water from sources other than mother's milk
would lead to overestimation of milk intake.
Fractional turnover rates of 0.168 and 0.152
correspond to body water half-lives of 4.1
and 4.6 days. Four-week-old beagle puppies
suckling bitches fed canned, semipurified
diets of high or low carbohydrate content
had somewhat longer half-lives of 5.0 and
6.8 days, respectively (9). These data were
not corrected for either isotope recycling or
changing size of the body water pool, how
ever. Baverstock and Green (12) calculate
that at least 47% of the isotope lost by dingo
puppies is ingested by the mother; some of
this is recycled to the young in milk. Isotope
recycling was not measured directly in the
present study although accumulation of
D2O in uninjected control puppies indicated
that it did occur.
The milk intakes determined herein are
much higher than the 81 ±13 ml/day and
59 ±13 ml/day reported by Romsos et al.
(9) for beagle puppies suckling bitches fed
two semipurified diets. Aside from the
methodological problems mentioned above,
these puppies exhibited abnormally low
growth rates, gaining on average only 13
and 11 g/day in the two groups. Normal
growth rates for beagle puppies are 35-40
g/day (17, 19, 42, 43). Records for the
Cornell dog colony for 1975-1976 indicate
average growth rates of 34.9 ±0.99 g/day
for puppies in litters of five (n = 25 pup
pies), 29.9 ±1.23 g/day for puppies in
litters of six (n = 30) and 27.2 ±1.08 g/day
for puppies in litters of seven (n = 35). The
growth rates observed in the present study
(36.8 ±1.28 g/day) for puppies suckling
bitches fed a commercial dry dog food are
somewhat above the colony norms, but
within the normal range for beagle puppies.
The semipurified diets used by Romsos et al.
(9) apparently did not support normal milk
yields.
The milk intake of 26-day-old puppies
was equivalent to 14.6% body weight, a
decline from the 17.0% of body weight
consumed at 19 days. Mundt and colleagues
(7) reported that milk intakes of puppies in
three litters of various breeds averaged
10.0-13.5% of body weight in the first 4
weeks postpartum. These data derive from
weights taken before and after puppies were
allowed to suckle. The experimental regi
men of separation and periodic, controlled
access of young to mother may cause a
reduction in secretion rates, may interfere
with normal maternal nursing behavior, or
may result in the accumulation of amounts
of milk that young are unable to consume in
relatively short suckling bouts (3). Hence
weight differential procedures tend to
underestimate milk consumption rates.
Mundt et al. (7) note that puppies consumed
more than 95% of daily milk intake in four
or five of the six suckling bouts permitted
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810 OFTEDAL
per day; i.e., one or two suckling bouts per
day were relatively unsuccessful. These
puppies reportedly consumed 1.7-3.0 g milk
per gram body weight gain in weeks 3 and
4 (7). By contrast puppies in the present
study were calculated to consume 4.4 g milk
per gram gain during week 3 and 4.8 g milk
per gram gain during week 4. On this basis
it appears that the weight differential pro
cedure underestimated milk intake by about
one-third.
Peak milk yields of beagle bitches appear
to be about 1 kg/day in week 4 postpartum.
Milk yield is undoubtedly influenced by
body size (2, 3). Using a weight differential
procedure, Russe (6) estimated that at 6
days postpartum a German shepherd pro
duced 915 g as compared to 102 g and 184
g for two dachshunds. Only the German
shepherd was studied throughout lactation;
peak yield (about 1.7 kg/day) was observed
at 22-27 days (6). Assuming a body weight
of 30 kg, milk production of this dog was
about 130 g/kg075 as compared to 157
g/kg°75for beagle bitches at 26 days post
partum in the present study. Bias associated
with the weight differential method may
explain some or all of this 20% difference
Nutrient intakes in relation to estimated
requirements. The Subcommittee on Dog
Nutrition of the National Research Council
(NRC) (44), following Payne (45), listed the
daily ME requirement of 3- and 6-week-old
puppies as 274 kcal/kg0'75. In the present
study puppies ingested only 244 kcal gross
energy per kilogram0 75at 26 days. If conver
sion factors of 4.0 kcal ME per gram protein
or sugar and 9.0 kcal ME per gram fat are
adopted, dog milk can be calculated to
contain 131kcal ME/100 g. The ME intakes
would then be 219 kcal/kg"7S at 19 days and
200 kcal/kg0 7Sat 26 days. It appears that the
National Research Council (44) overesti
mated the metabolizable energy needs of
young puppies by 25-35%.
Recently Mundt et al. (7) estimated the
daily maintenance requirements of puppies
as 72 kcal gross energy per kilogram0 75from
a regression of gross energy intake of suck
ling puppies on growth rate. As the milk
intakes of the puppies were probably under
estimated by a substantial amount (see
above), this estimate cannot be considered
reliable
Weaned puppies have been estimated by
the Subcommittee on Dog Nutrition, NRC
(44) to require 22% protein in the dry
matter of a diet containing 3.5-4.0 kcal ME
per gram dry matter. Dog milk contains
about 131 kcal ME/100 g or 5.77 kcal ME
per gram dry matter, a value about 50%
above the NRC diet. If dog milk is to meet
NRC requirements it should contain 1.5
x 22 = 33% protein on a dry matter basis.
The protein content of dog milk was indeed
found to be 33.4% of dry matter.
Puppies ingested 0.33 g protein per gram
body weight gain at 19 days and 0.36 g
protein per gram body weight gain at 26
days. Payne (45) assumed weight gain in
puppies to contain 17% protein, whereas
carcass analyses by Sheng and Huggins (25)
indicate protein content to remain at about
10-12% of body weight from birth to 6
weeks postpartum. At peak lactation pup
pies apparently incorporate only one-third
to one-half of ingested protein into tissue
ACKNOWLEDGMENTS
I would like to thank Dr. Richard G.
Warner for authorizing use of the dog
colony at Cornell University, Dan Shattuck
and staff of the colony for care of the ani
mals and assistance with milk and blood
collection procedures, and Dr. Charles
Roberts and David Dance of the Smith
sonian Institution for performing statistical
analyses. Milk analyses were conducted in
the laboratory of Dr. John Sherbon. Drs.
Maiden C. Nesheim and Harold E Hintz
offered constructive criticism and support.
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