Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

IV. Clinical Aspects of Reproductive Endocrinology
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days 20 and 26 of pregnancy. Horne et al. (1983) found litter
size on days 20 to 26 of pregnancy to be positively correlated
with estrone sulfate values but such a relationship
was not found later in pregnancy. During the latter part of
pregnancy, the maternal blood concentrations of estrogens
(estrone sulfate, estrone, and estradiol-17 β ) are very high
and can thus be used to confirm pregnancy at this stage of
gestation ( Fig. 21-6 ).
In the pregnant sow, the concentration of estrogen in
urine and feces follows the same pattern as in blood ( Choi
et al. , 1987 ). Szenci et al. (1993) compared ultrasonography
and the determination of unconjugated estrogen in
feces, 25 to 30 days after insemination, for the diagnosis
of pregnancy in pigs. Based on farrowing data the positive
and negative predictive values for the ultrasound were 93%
and 100%, respectively. For the determination of unconjugated
estrogens, the corresponding predictive values were
94% and 55%, respectively.
D . Horse
1 . Equine Chorionic Gonadotropin
Although pregnancy diagnosis has been done in mares
through the measurement of equine chorionic gonadotropin
(eCG) formerly named pregnant mare serum gonadotropin
(PMSG), the main drawback to its use is that the presence
of eCG does not guarantee the presence of a fetus but indicates
that a viable fetus was present at the time of endometrial
cups formation. This is because endometrial cups have
autonomy of function and continue to secrete PMSG for
a period of time in spite of loss of the fetus ( Allen, 1969 ).
This means that both mares with normal pregnancies and
mares that experience embryonic mortality after day 40 of
gestation will have elevated eCG concentrations in blood.
The use of eCG determinations as a positive pregnancy
diagnosis test will consequently yield some mares to have
been diagnosed pregnant but not delivering a foal ( Fig. 21-8 ;
Jeffcott et al. , 1987 ; Mitchell, 1971 ). Complementation with
estrone-sulfate measurements after 100 days of pregnancy
can compensate for this shortcoming.
2 . Progesterone
Progesterone analysis is useful for establishing the presence
or absence of ovarian activity in animals with puzzling
behavioral patterns. Agitated or aggressive behavior,
often interpreted as sexual in orientation, occurs without
regard to luteal status. Progesterone analysis can be helpful
because elevated values directly indicate the presence of
a CL and, additionally, are evidence that folliculogenesis
and ovulation are normal. Relatively low luteal phase values
for progesterone (1 to 3 ng/ml; 3 to 10 nmol/liter) versus
normal luteal phase values ( 3 ng/ml; 10 nmol/liter)
are often associated with the presence of a persistent CL
( Stabenfeldt et al. , 1974a ). Progesterone values of mares
with persistent luteal activity are low because some PGF 2 α
synthesis and release often occurs about 14 days postovulation,
albeit insufficient to cause complete luteolysis ( Neely
et al. , 1979 ).
Progesterone analyses can also be useful in mares that
fail to manifest sexual receptivity yet have cyclic ovarian
activity. Progesterone analysis at 5-day intervals over
20 days (approximately one estrus cycle length) can verify the
presence or absence of cyclic ovarian activity. The time of
ovulation can also be predicted within a 2- to 3-day interval,
a prediction that can be helpful to the veterinary practitioner
anticipating the next time of ovulation. Breeding may have
to occur by artificial means in these situations. Hinrichs
et al. (1988) compared the accuracy of determining day
of ovulation 1 day using three different methods: (1) an
immediate, qualitative ELISA for progesterone in blood;
(2) a quantitative ELISA for progesterone in blood; and
(3) daily teasing to detect estrus. Ovulation was detected by
ultrasound examination per rectum. The accuracy in determining
day of ovulation 1 day using the three methods
was 72% for the qualitative progesterone assay, 88% for the
quantitative progesterone assay, and 86% for teasing.
3 . Conjugated Estrogens
Estrone in its unconjugated form (free estrogen) reflects
important physiological events in the mare beginning
at about day 75 of gestation when the fetoplacental unit
begins to produce estrone in rapidly increasing amounts
(Nett et al. , 1975 ). More important, it has been shown
that estrone is rapidly conjugated after secretion to watersoluble
estrogen conjugates and the ratio between free
and conjugated forms is 1:100 ( Terqui and Palmer, 1979 ).
Terqui and Palmer (1979) and Kindahl et al. (1982) have
both shown that significant increases in estrone conjugate
concentrations occur between days 35 and 40 of gestation
(Fig. 21-8 ). Kindahl et al. showed the increase to be 10-
to 20-fold between days 35 and 40. Concentrations then
decline slightly with a further increase noted at the same
time that free estrone concentrations begin to increase. The
initial source of increased estrone production during gestation
days 20 and 70 is the ovaries ( Daels et al. , 1990 ); later
on its occurrence is likely driven by the attachment of the
embryo and the production of eCG (PMSG). A study in
miniature mares showed that the determination of estrone
sulfate concentrations in blood after day 100 of pregnancy
is a reliable method for determining pregnancy status, as
well as eliminating “ false-positive ” diagnosis by eCG measurements
between day 40 to 100 ( Henderson et al. , 1998 ).
Also estrone conjugate concentrations in urine can be
used to document pregnancy in the mare and, in fact, may
be more accurate than plasma analysis because of the concentrating
aspects associated with urine formation ( Daels
et al. , 1991 ). Increased amounts of fecal estrogens and