Objective—To evaluate changes in protein and nutrient
composition of milk throughout lactation in dogs.
Sample Population—Milk samples collected from
10 lactating Beagles.
Procedure—Milk samples were collected on days 1,
3, 7, 14, 21, 28, 35, and 42 after parturition and analyzed
to determine concentrations of nitrogen, nonprotein
nitrogen, casein, whey proteins, amino acids,
lipids, lactose, citrate, minerals, and trace elements.
Optimum conditions for separating casein from whey
proteins and distribution of milk proteins throughout
lactation were assessed by use of polyacrylamide gel
Results—Protein concentration was high in samples
collected on day 1 (143 g/L), decreased through day 21
(68.4 g/L), and increased thereafter. Concentration of
nonprotein nitrogen did not change throughout lactation
(5.7 to 9.9% of total nitrogen content). Casein-towhey
ratio was approximately 70:30 and remained constant
throughout lactation. Lactose concentration
increased from 16.6 g/L on day 1 to 34.0 to 40.2 g/L on
days 7 to 42. Lipid concentration ranged from 112.5 to
137.2 g/L. Citrate concentration increased from day 1
(4.8 mM) to day 7 (6.6 mM), then gradually decreased
until day 42 (3.9 mM). Iron, zinc, copper, and magnesium
concentrations decreased during lactation,
whereas calcium and phosphorus concentrations
increased. Calcium-to-phosphorus ratio remained constant
throughout lactation (approx 1.6:1). Energy content
of milk ranged from 1,444 to 1,831 kcal/L.
Conclusions and Clinical Relevance—Protein and
nutrient composition of milk changes throughout lactation
in dogs. These data can provide valuable information
for use in establishing nutrient requirements
of puppies during the suckling period. (Am J Vet Res
Objectives—To determine uptake of β-carotene by
ovarian and uterine tissues and influence of dietary β-
carotene on steroidogenesis and production of uterine
protein during the estrous cycle in cats.
Animals—56 female cats.
Procedure—Cats were fed diets containing 0, 0.4, 2,
or 10 mg of β-carotene daily for 8 weeks prior to
detection of estrus. At time of observed estrus, all
cats were manually induced to ovulate. Blood samples
were obtained at estrus and every 2 days until
day 14 after ovulation. On that day, cats underment
laparotomy, and the ovaries and uterus were
removed. Uterine contents were flushed, and luteal
and endometrial tissues were obtained.
Results—Concentrations of β-carotene in plasma and
luteal and endometrial tissues increased in a dosedependent
manner. Concentrations of plasma progesterone
were higher between days 6 and 10 after
ovulation in cats fed diets containing β-carotene and
continued to increase through day 14 after ovulation
in cats fed a diet containing 10 mg of β-carotene.
Plasma concentration of estradiol-17β also was higher
between days 0 and 4 after ovulation in cats fed
diets containing β-carotene. Cats fed a diet containing
10 mg of β-carotene had the highest plasma estradiol
concentration. Total uterine protein concentration
was higher in cats fed β-carotene, compared with values
for cats fed an unsupplemented diet.
Conclusion and Clinical Relevance—Cats readily
absorb β-carotene. Increased concentrations of progesterone,
estradiol, and uterine protein may provide
more optimal ovarian function or a better uterine environment
for embryonic survival and development.
(Am J Vet Res 2001;62:1063–1067)
Objective—To study the musculoskeletal development
of Great Dane puppies fed various dietary concentrations
of calcium (Ca) and phosphorus (P) in
fixed ratio by use of dual energy x-ray absorptiometry
(DEXA), determination of serum insulin-like growth
factor I and parathyroid hormone concentrations,
radiography, and blood chemistry analysis results.
Animals—32 purebred Great Dane puppies from 4 litters.
Procedure—At weaning, puppies were assigned randomly
to 1 of 3 diets. Blood was collected for biochemical
analyses and hormone assays, and radiography
and DEXA were performed through 18 months of
age. Changes in body weight, bone mineral content, fat
tissue weight, lean mass, result of serum biochemical
analyses, hormonal concentrations, and radius lengths
were analyzed through 18 months of age.
Results—Bone mineral content of puppies correlated
positively with Ca and P content of the diets fed.
Significant differences between groups in bone mineral
content, lean mass, and body fat were apparent
early. The disparity among groups increased until 6
months of age and then declined until body composition
was no longer different at 12 months of age.
Accretion rates for skeletal mineral content, fat, and
lean tissue differed from each other and by diet group.
Conclusions and Clinical Relevance—Ca and P concentrations
in the diet of young Great Dane puppies
are rapidly reflected in the bone mineral content of
the puppies until 5 to 6 months of age, after which
hormonal regulation adjusts absorption and excretion
of these minerals. Appropriate Ca and P concentrations
in diets are important in young puppies < 6
months of age. (Am J Vet Res 2002;63:1036–1047)