Progesterone, 2OfLHydroxypregn4en3one, and Luteinizing Hormone ...

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Feb 20, 1973 - john Company,. Kalamazoo,. MI 49001. 'Present address: Department ... Armour-Baldwin. Labs) given intravenously to induce ovulation. They.
BIOLOGY

OF

9,

REPRODUCTION

Progesterone,

116-124

(1973)

2OfLHydroxypregn4en3one,

Hormone

Levels

in Superovulated Postpuberal

C.

H.

SPILMAN,2 C. R.

Department

G. E. VUKMAN,

of Animal

and

Science,

Prepuberal

and

Cattle1

SEIDEL,

JR.,3 L. L. H. FOOTE

R.

AN])

Cornell

Accepted

Luteinizing

University,

February

20,

LARSON,4

Ithaca,

New

York

14850

1973

Pituitary and plasma luteinizing hormone (LH) and luteal and plasma progesterone were measured in 47 prepuberal Holstein calves and in eight postpuberal heifers for 30 days after induced ovulation or superovulation. Mean pituitary LH in six of the eight heifers sacrificed 30-31 days after superovulation averaged 1.1 mg LH/g of pituitary tissue. Plasma LH rose to 7.2 ng/ml the day after PMSG injection and gradually declined to normal levels of about 2 ng/ml. Plasma progesterone peaked at 63 ng/ml 10 days after LH injection to induce superovulation and declined to nearly undetectable levels in three of the heifers by Day 24. These three heifers ovulated spontaneously, plasma progesterone rose to 8.3 ng/ml by Day 28, and each had a new active corpus luteum at slaughter. The others had not ovulated when slaughtered on Day 30, and still had some old active luteal tissue. Mean pituitary LH in control calves was 5.0 mg/g of wet pituitary tissue and ranged from 0.7 to 1.6 mg/g during the 30 days after superovulation. Plasma LH in calves rose from 1.5 ng/ml before injection of pregnant mare serum gonadotropin (PM SC) to 5.5 ng/ml the day after PMSG and returned to the original level by 10 days after PMSG. Calf corpora lutea had a maximum average progesterone concentration of 43 g/g of luteal tissue 10-11 days after ovulatory LH. This declined to a minimum on Day 28, but some calves had as much as 36 g progesterone/g of luteal tissue on Day 30. Plasma progesterone rose to nearly 100 ng/ml 8-10 days after superovulation, and peak progesterone was correlated with the number of corpora lutea (r = 0.76, P .( 0.01). Plasma progesterone declined after Day 15, but detectable levels were present

throughout

the

experiment.

Plasma

progesterone

and

20p-hydroxypregn-4-en-3-one

rose and fell simultaneously in eight superovulated calves. The major difference among the prepuberal and postpuberal animals was the fact that plasma progesterone in the prepuberal animals never declined to essentially undetectable levels and none ovulated spontaneously. Whether this reflects a difference between uteri of immature and mature cattle in regulating corpus luteum function has not been investigated.

No

information

ture

was

concerning

1This

work

was

found

in

possible

cyclical

partially

supported

litera-

the

in

by

Grant

itary

from the National Institute of Child Human Development. ‘ address: Fertility Research, The Upjohn Company, Kalamazoo, MI 49001. ‘Present address: Department of Physiology and HD 03471 Health and

Biophysics, CO

Colorado

State

University,

“Present

address:

Department

of Nebraska,

of Lincoln,

#{174} 1973 by of reproduction

The

Society for in soy form

they

Ft. Collins, Animal SciNB 68503.

the Study reserved,

levels

of LH

of Reproduction.

can

(LH)

ovulation cattle, in dairy

(Desjardins

Calves normally at about 8-12

116 Copyright All rights

hormone

after induced in prepuberal

measured

80521.

ence, University

luteinizing

terone lation

changes

be

start months induced

or

calves and

Hafs,

to ovulate of age. to

proges-

or superovualthough pitu-

ovulate

ogenous

gonadotropin

treatment

month of and Hafez,

age (Marden, 1970; Seidel

1953;

have

been 1968).

and cycle However,

with

exat

Lineweaver et a!., 1971). Pro-

1

PROGESTERONE

AND

LII

IN

SuPEROvULATED

cor-

-15#{176}C for

pora lutea by Marden (1953). The in vitro steroidogenic capabilities of luteal tissue from superovulated calves have been deter-

determination.

gesterone

was

mined progestin

have

secretion

postpuberal

in

uteri

superovulate with

were

similarly

sexually of

In

were

and

heifers,

comwhich plasma

group

AND

METHODS

The superovulation regimen for calves has been described in detail (Seidel et al., 1971). Briefly, 47 Holstein calves, 2-5 months old, were given 1250-2000 IU of pregnant mare serum gonadotropin (PMSG) intramuscularly, followed in 5 days by 75 mg LH (PLH, Armour-Baldwin Labs) given intravenously to induce ovulation. They were laparotomized 3 days after the injection of LH in order to examine the ovaries and to recover ova. The calves were subsequently sacrificed at regular intervals from 5-30 days after LH administration. Eight cycling postpuberal heifers were injected intramuscularly on Day 15 or 16 of the estrous cycle with 3000 IU PMSG followed in 4 days by 2500 IU human chorionic gonadotropin (HCG) given intravenously. They were sacrificed at

either

30

or

31

days

after

HCC.

The

pituitaries

from all animals were quickly removed and frozen. The ovaries were removed and approximately 0.5 g of luteal tissue was taken from several corpora lutea of each animal and stored at -15#{176}C for later extraction. Ten to fifteen milliliters of blood were collected from the jugular vein of calves 5 days before the PMSG injection and from calves and heifers on alternate days from the day of PMSG injection to the day of LH or HCC injection. On the days that PMSG and LH or HCG were injected, blood was collected prior to the injection and then not again for at least 24 h. For the next 5 days, 200-250 ml of blood were collected from each animal on alternate days and thereafter every 4 days. More frequent bleeding was avoided to minimize stress and hemodilution. After centrifugation, the plasma was removed, frozen, and stored at

in

a

and

(1:2,

developed

systems of Armstrong ples were transferred developed in isopropyl

was

of

alka-

times

silicic a

by

with

3

were spotted on plates prepared acid

Chemical

(Silic

at

in

two-dimensional

thickness

et al. (1964). to a second ether-ethyl

AR in dis-

Works)

w/v) the

made

funnel

Samples (tic)

slurry

plasma

(1970)

three

separatory

LH

the

Hansel

extracted a

and

from

and Plasma

and

Mailinckrodt

7CF,

of

0.25

solvent Usually,

tic

plate

acetate

samand (5:2,

v/v). After

in one

modification.

spreading

mm

extracted

diethyl ether. chromatography

tilled water

or

of calves. MATERIALS

vol of thin-layer

extraction

of Kazama

shaking

with

ovulate

was

NaOH

cattle

addition,

determined

a slight

with

TLC

20/3-hydroxypregn-4-en-3-one

(20$-OH-P)

with

line

by

steroid

procedure

with

to

mature

treated.

the

cattle

et a!., 1971)

(Seidel

pared levels

induced

later

Progesterone

by

vigorous

to compare posLH and proges-

Prepuberal

were

calf

1972), but plasma not been reported.

prepuberal

cattle.

infantile

in

was initiated changes in

study

cyclical

terone

identified

et a!.,

(Spilman levels

This

sible

first

117

CArrLE

the

final tic

separation,

progesterone

and

20k-OH-P spots were eluted with diethyl ether or chloroform and quantitated by gas-liquid chromatography (glc). The glass columns were packed with either 2.5% SE-30 or 3% OV-225 on GasChrom Q. Sample progesterone and 20p-OH-P peaks were identified by comparing their respective gic retention times against the retention times for authentic compounds. Plasma progesterone values obtained by this method in the same laboratories for mature cycling cattle were normal (Hansel and Echternkamp, 1972). All samples were corrected for procedural losses. Tritiated 20p-OH-P was obtained by enzymatic reduction of [7-’HJ progesterone. Luteal tissue was minced and extracted by refluxing in ethanol (Seifart and Hansel, 1968). Progesterone was isolated by the same tic procedures used for plasma and quantitated by uv absorption at 240 nm. Corrections were made for background from 225-255 nm (Allen, 1950). Plasma LH levels were determined by radioimmunoassay (RIA) following the procedure given in detail by Harms et al. (1969). This method, in simultaneous studies on mature cycling cattle (Hansel and Echternkamp, 1972; Hobson and Hansel, 1972), measured about 1.5-2.0 ng LH/ml plasma during the estrous cycle. Three aliquots of 0.2 ml were used to determine plasma LH in each sample. Triplicate NIH-LH-B7 standards were run with each assay. To determine whether injected PMSG might affect the LH assay, levels of PMSG likely to be found in blood plasma after

an

intramuscular

injection

were

also

assayed.

As reported by Niswender et al. (1968), no cross reactivity was found between PMSG and the LH antibody used in the RIA. Pituitary LH was determined in the initial group of calves by the ovarian ascorbic acid depletion (OAAD) method (Parlow, 1981). Two levels of each pituitary, 0.4 and 1.6 mg wet weight, and

118 0.4, in

SPILMAN

1.6, 1.0

and

ml

6.4 g

were dissolved into rats (five

of NIH-LH-B5

of saline and injected which had been primed

per level), with PMSC and HCG. Statistical analysis of the assay data was done by the methods described by Finney (1952). Subsequently, additional calves were examined for a longer interval of time after superovulation. The pituitaries from these calves and from all heifers were analyzed for LH by RIA. They were homogenized in phosphate-buffered saline-1% egg white. Appropriate dilutions were made and the samples were assayed in triplicate. NIH-LH-B7 was used as the standard.

RESULTS

AL.

six

Pituitary

and

Mature

after of

to

the

heifers

was

nearly

be present

sacrificed

about 2 study, 30

or

averaged

pituitary.

content

Thus,

of adult

1.1

pituitary

tissue

superovulated

normal

after

animals

superovulation

Plasma (Fig. 1)

LH in sexually rose sharply after

and

declined

Day

5 the

at three

gradually

for

normally

had 15

et a!., 1972).

spontaneous

and

slaughter of

levels

cycling

1969; Henricks Echternkamp,

these

LH

although

26,

on

Days had

heifers injection

thereafter.

LH

plasma

mature PMSG

(Harms

1970; Five

Hansel of the

peaks it was

30 ovulated

or

After

similar

were cattle

31

between observed

that

only

recently.

S E 0, C C Ui

z 0 U)

Ui I-. U) Ui

A-

0 0 A.

U,

A.

DAYS

Fxc.

1. Blood

ovulated

with

AND

AFTER

OVULATORY

LII

progesterone concentrations in sexually mature heifers superThe number of samples assayed are noted at each point. After Day 22 the progesterone values for the three heifers that ovulated are shown separately (solid dots) from the rest (open circles). PMSG was injected on Day -4 and HCG on Day 0 after taking blood on those days. The standard errors for plasma LH were 0.2, 3.3, 0.1, 0.5, 0.2, 0.7, 0.3, 0.4, 0.3, 0.2, 0.3, 0.4, 0.4, 0.5, 0.1, 0.2, 0.2, and 0.3. The standard errors for plasma progesterone were 1.2, 5.7, 22.7, 20.3, 13.8, 24.4, 31.2, 8.5, 3.2, 3.2, and 1.0 ignoring the separation into two groups after Day 22. plasma

PMSG

LH

and

and

BEFORE

HCC.

31 mg

treatment.

Days

sexby

(1966) In

superovulation

LH

heifers

LH concentration of cattle has been reported

tissue.

postpuberal

days LH/g

and

LH

Plasma

The pituitary ually mature

Heifers

a!.

of fresh

et a!., Superovulated

et

Desjardins

mg/g

to those

DISCUSSION

AND

ET

PROGESTERONE

LH

AND

IN

SUPEROVULATED

TABLE LH

CONTENT

OF

ANTERIOR

1

PITUITARIES

LH

119

CATTLE

FROM

SUPEROVULATED

concentration,

CALVES

Total

LH

No. Treatment Untreated Days

_________________

calves

Mean

4

5.0

3.7-7.0

2.3

1 .6-3.3

controls after

of

content,

m g’

mg/gb

Range

Mean

flange

LH

5

3

1.2

0.7-1.5

0.6

0.4-0.7

10

4

1.6

0.9-2.5

0.9

0.5-1.2

15

4

1.3

0.9-1.6

0.7

0.4-0.9

20

5

0.9

0.5-1.3

0.5

0.3-0.9

22

6

1.0

0.2-2.2

0.3

0.1-0.5#{176}

24

6

0.9

0.2-1.7

0.6

0.1-1.2

26

6

0.7

0.3-1.0

0.5

0.3-0.7

28

5

1.5

0.6-2.4

1.0

0.4-1.6

30

4

1.6

0.8-2.2

0.8

0.3-1.0

Samples from control calves and from treated calves taken for 20 days after LH were assayed by the OAAD method. Subsequent samples were assayed by RIA. There were no differences (P > 0.10) among the LH-treated groups, but the untreated controls were different from all other groups (P < 0.005). ‘The

mean

lost from

total LII

the other

Luteal

and

At

Plasma

slaughter,

two

for this group

three

corpora

heifers,

again,

lutea

which

averaged

g progesterone! the progesterone lutea in some

is based

0.8,

from

had

9.5,

not

and

21.4

g of corpus luteum. Thus, concentration of corpora animals was maintained

longer than in normal cycling heifers (Hafs and Armstrong, 1968) in which luteal progesterone declined sharply after Day 18. Three

other

heifers

each

had

corpus Days

luteum formed before 30 or 31. The progesterone

tion

was

measured

was 52.1 Plasma by Days (P

in

two

between

Days

days

sampled.

Lamond

(1972)

study heifers. reported

found

values

similar

in

the

present

higher

than

normally

cycling

or

(Henricks

kamp,

single

slaughter on concentraof

these

10-22

than

and to the

those pregnant

are

reported dairy

et a!., and

The lutea

calves,

three when

since

some

pituitary

heifers that slaughtered

undergoing

a nearly

progesterone nearly

in

tissue

increased

Day

23.

was

that

reported

animals. into

by

during Three

(1972)

estrus

Hansel

and

midcycle heifers

in that

ovulate

levels

Day of

slightly

on Day

slaughtered

ng/ml

Plasma

declined

on

is

and

plasma

tectable

6.3

value

corpora were

cycle.

animals levels

to

This

had new apparently

normal

these

undetectable

then

to

24

and

plasma higher

by than

Echternkamp mature did not

dairy come

maintained

de-

of progesterone

until

30 or 31.

Superovulated

Pituitary The

on of

Caddy present

study

et a!., 1970; Plotka et a!., 1968; Hansel 1972).

three

and

luteum. had risen greater

on Day 15 in superovulated beef The levels of plasma progesterone

nificantly

Shemesh

a new

of corpus (Fig. 1) significantly

and 84.3 zg/g progesterone 3 to 5 and was

< 0.01)

other

on

at slaughter.

Progesterone

postpuberal

ovulated

content

calves

sig-

for cows

1967; Echtern-

and

calves ously (Desjardins ovulation,

LH

Plasma

mean

pituitary

LH tissue

(Table published

1)

Calves

concentration for

of 5.0

untreated

agrees with for calves

mg/g

prepuberal

values previof this age

and Hafs, 1968). After superpituitary LH levels decreased

markedly (P < 0.005), approximating those found in mature animals (Desjardins et al., 1966). Levels remained low,

al-

though

it appears

in-

creasing

slightly

they

may

by 30 days.

have

been

120

SPILMAN

ET

AL.

12 .

5.5 5.0

7-\

!16

100

/

4.5 4.0

14

/

E

/

01 C

18

.

:

3.0

-J

Ill

\

/

9o

\

0)

\

Ui

z

\

/

2.0

:

28

U, Ui

0

50

0

:

:

..

25

A.

9

40

‘C

..

:

26

....#{149}.. 39

12

Ui

I-.

25

13

60

.

29

18

0

:

-i

0.

C

:

Progesterone

-

2.5 .1l

S -_

80

: U)

110

26

16. ...I#{149}

18

18

30

U,

:

A.

‘C

0

#{149}k#{149} II

0

III

III

-10

5

DAYS

Fic. 2. and LH. -5 and were 0.1, and 2.7. 26.1, 9.3,

Plasma

values

postpuberal Henricks

ment

a!.,

the

1970;

and

AND

the

declined

et

(Harms Hansel

gradually

(P < 0.01).

levels

control

6 and 26. The observed due calves sions

rise

injection solely

(Fig.

to LH

creases tration.

LH

apart

in plasma Levels

of

plasma after not detectable

LH

assay Niswender

used.

in

plasma

1)

is believed

30

LH

on

two

LH after PMSG

PMSG likely

intramuscular when checked agrees

This

et

a!.

(1968),

with

of

LH

1971).

Estrogen

after

in-

release

of

1969;

PMSG

estrogen

and has

follicles.

was on

the

injection by the

this

injection

cattle

(Hobson

from

may

the

previous on

injection

be

3 h,

than

Since

plasma

injection, of the

on

the

day

because

The small LH due to residual of 75 mg of

be

day.

a!.,

phenomenon in superovu-

administered first.

1

24 h after in the blood less

et

and

collected Day

the

(Coding

A similar to occur

was

to a!.,

et causes

sheep

(Midgley et a!., 1968). peaks were observed LH

es-

calves

administration

in

et a!., 1971)

lated rats No LH blood

these (Seidel

by

Hansel, 1972). been reported

peak

secretion Sufficient

estrus

LH

Bolt

LH

found

following

behavioral

hormone

work

between

produced

exogenous

occa-

reactivity

PMSG-stimulated

administo be in

the who

release

was

to be

similar

cross

the antibody used in our RIA. The in LH presumably reflects endogenous

trogen induce

additional

showed

little

and rise

had in-

in one

LH

Four

PMSG

with

days

the were of

OVULATORY

by

to pretreat-

Plasma

secretion.

injected 32-33

AFTER

25

20

and

calf that did not ovulate after LH injection varied from 0.6 to 1.2 ng/ml between Days

PMSG

1111111

15

very

al.,

These values day after PMSG

1972).

considerably

jection

BEFORE

(Fig. 2) are for normally

cattle

et

Echternkamp,

risen

during

before superovulation to values reported

cycling 1969;

liii

JO

Blood plasma LH and progesterone concentrations in calves superovulated with PMSC The number of samples assayed are noted at each point. PMSG was injected on Day LH on Day 0 after taking blood on those days. The standard errors for plasma LH 0.1, 0.4, 0.6, 0.4, 0.3, 0.2, 0.3, 0.2, 0.1, 0.2, 0.1, 0.1, 0.2, 0.1, 0.3, 0.1, 0.1, 0.2, 0.5, The standard errors for plasma progesterone were 0.7, 0.4, 1.5, 9.9, 7.8, 14.7, 33.0, 13.3, 12.0, 8.2, 2.3, and 2.7.

LH

period similar

111111

.1111111

0

LH

the was

effect

of

minimal

the half-life of calf would appear

LH to

PROGESTERONE

Five 5.2,

to

had

calves

4.8,

and

20.

4.8

Owing

pling,

undetected

cured

in

contrast heifers

LH

peaks

calves.

had The

of

5.4, 15

blood

may

up

to

Day

in one

the these

of the

were

and

Plasma

Superovulation sive production tissue.

sg/g

rise in an LH

calves

days

lutea

slaughtered

after

LH

luteal

tissue

3,

10,

15,

respectively. lutea per

often

exceeded

PMSG

0.9,

Also,

With animal

an the

corpora maintenance. Plasma

Average

progesterone

concentration

luteal (Table

tissue from superovulated 2) was similar to that

cycling

cows

through

Armstrong,

1968).

Luteal

began Day 11

to and

tained tle

in which

than

of

progesterone decline reached

in most a mini-

cycling

levels

or about Day 18 (Armstrong 1966; Hafs and Armstrong,

decline and 1968).

on

CONCENTRATION

OF

CALF

Day Item

Number

5-8

10-11

and lutea

Hafez,

blood

the

1970;

flow

greatly

to

different

the

plasma

levels

indicating

not

a calf

that

4

and Peak

correlated 0.76, low at

=

to have lower titers just prior to slaugh-

was

from

of were

of CL (r Calves having concentrations

progesterone

Progesterone

were

high mass

Days times.

samples

calf lutea

were large

between at other

tended

prorest.

corpora levels

of

progesterone

Mar-

enlarged

affected

tissue

also

after

1971), thereby older than the

significantly higher 26 (P < 0.01) than

TABLE PROGESTERONE

days

Levels

ter.

Black, They

20

present.

slaughter of plasma

cat-

calf

et a!.,

a result

luteal

the

ovulaby the

have

as

calves,

progesterone/g

result from a few being induced

with the number P 0.05).

122

SPILMAN

not

cause

progesterone

absence

of luteal

Plasma Since

20/3-OH-P of

with

may

superovulated

clear

that

was

much peak

higher.

The to

(Hafs

(Fig.

3).

a

same as of pro-

data

indicate was

it was

reported

6-18%

and

It

et a!.,

in 20-OH-P have

The lation

Levels

from

that

of

progesterone

levels Woody

been

shown

that

after

plasma

tissue

heifers

1968;

1968)

recattle.

and in

there levels

of pro-

Discussion

level of indicates

pituitary

LH

that

after a rate

is

superovuof release to

similar

1.

130

E 110 C

A.

-Progesterone

I

20f1.OH.P

0 0

03

z Lii

z 0 :. U., I‘I,

\

.:

U.,

0 0 A.

‘C

‘C A.

..

1-2

3-5

10-11

5-7

DAYS Fic. OH-P) The

3.

Relationship

in blood standard

between plasma

errors

plasma

of eight

35.0, 23.7, and 9.4. Those 9.2, 12.1, 0.1, and 3.2.

for 20p-OH-P

8

were

after

20

22

OVULATORY

progesterone

calves

for progesterone

14-15

AFTER

and inducing

were

24

26

28

LH 20p-hydroxypregn-4-en-3-one

superovulation

0.1, 1.0, 0, 16.2,

the

is a sharp

fallen.

plasma of calves the

been

luteal

postpuberal

has

General

being

not

in

Armstrong, 1968).

gesterone

have

or postpuberal

20/3-OH-P

about

rise

It

the value

20/3-OH-P.

20/3-OH-P prepuberal

in

Ginther, rat (Wiest

followed

apparently

reduced

were

cattle,

progesterone

also

the

progesterone

continually

of

very

but

major

in

compared

calves

pattern

plasma

first

it were

20/3-OH-P

progesterone,

gesterone

the

concentrations

eight

of

however, levels of

20/3-OH-P

be of

is

that

and

progesterone

in

curvilinear

the

tissue.

concentrations plasma

in

AL.

ported

Progesterone

metabolite plasma

production

ET

4.4, 47.6,

3.2, 3.1, 3.2, 10.8,

(20p-

with

PMSG

and

56.5,

31.0,

20.0,

0.9, 21.9,

17.0,

47.3,

LH. 39.1, 7.7,

that

PROGESTERONE

in

normally

the 1)

calf was

cycling

AND

mature

pituitary content not replenished

LH

cattle.

of after

IN

Since

LH (Table superovula-

SUPEROVULATED

ovulations. Consequently, no “cycles” apparently were induced in these calves. It would be of interest to determine whether

tion, a reduced rate of LH synthesis is indicated. This is evidenced by the fact that the plasma levels of LH were very similar

the

before

waska

superovulation the

whereas

significantly superovulation. feedback of tion

of

Either progesterone

LH

in

some duction

higher would

itary

LH.

level, release

and

on

pituitary content higher before than

the

a

Days

5-25,

of LH it was

was after

direct on the

anterior

pituitary

In

spite

of

this

LH low

low

calves

32

or

33

days

after

on

for into

original

A plasma

LH peak from six each

by a terone.

sharp These

ovulation

calf,

was calves the

measured on Days

LH

decrease changes

precocious However,

unable

to

cycling if so, the

respond

since

The high plasma these superovulated

tissue,

culating the high

plasma

precipitously

mature

heifers,

terfered

with

gression. lay, three

PMSG

kindly

was

(Lukasze-

LH-B5

and

tion, C.

Inc.,

by

We E.

LH

concerning

tance

Mrs.

Cole,

Mr.

Trout NIH-

Study

grateful the

Sec-

to

LH

Dr.

antiserum

Jr. for supplying

Dr.

puri-

Hansel for suggestions The technical assisMiss J. Wiebold, Mr.

W.

manuscript.

Pierro,

R.

Lindsay

Dr. the

Endocrinology

Reichert,

L.

Dr. by

and

supplying

and

the

of

PLH

especially

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L.

to Dr.

the

are

Niswender

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by

the

Laboratories,

B7

NIH. D.

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Mr.

Ball

is

typical cyclical of progesterone a subsequent

might

no

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of calves

progesterone primarily not of

normal

progesterone and heifers production by the mass

elevated

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J. Gun.

ARMSTRONG,

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was no precise time after at which luteal regression

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