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

IV. Clinical Aspects of Reproductive Endocrinology
649
diagnosis, pregnancy status needs to be verified again at
about 40 days postbreeding. In spite of the limitations of
progesterone analysis as concerns pregnancy diagnosis,
this is the most common clinical use of any of the reproductive
hormones. Progesterone analysis can also be used
for the retrospective confirmation of the absence (or presence)
of a CL at the time of insemination in cattle. Because
inadequate detection of estrus is the most common cause
of low fertility in herds utilizing artificial insemination, the
determination of progesterone concentrations at the time of
insemination can be a useful tool when herds with fertility
problems are encountered. The use of progesterone determinations
in milk obtained at the time of insemination in cows
with questionable heat signs and inconclusive genital tract
findings can serve as a valuable tool for educating the staff
responsible for insemination ( Garcia and Edqvist, 1990 ).
A potential important area for the diagnostic use of
progesterone analysis concerns the elucidation of clinical
syndromes in the postpartum period in which cows fail
to show sexual receptivity for extended periods of time.
Animals that have reestablished ovarian activity can often
be distinguished from those that have ovarian inactivity;
elevated progesterone values indicate that significant ovarian
activity is present. Cows that have luteal activity can
be manipulated through PGF 2 α treatment with a reasonable
expectation of response as concerns the initiation of
a new cycle. Progesterone determinations could also be
used to verify the presence of luteal tissue in conjunction
with endometritis/pyometra ( Pepper and Dobson, 1987 )
and ovarian cysts ( Booth, 1988 ; Sprecher et al. , 1990 ).
Both conditions should respond to prostaglandin therapy.
As concerns ovarian cysts in cattle, differentiation of luteal
versus follicular cysts is usually not done because it is
technically difficult by palpation per rectum and because
the same gonadotropin treatment can be used in both situations;
luteinization of the structure with a luteotropin is
followed in 10 to 14 days with prostaglandin treatment. In
both cases though, the use of progesterone analysis would
be useful in establishing the therapeutic response.
2 . Estrone Sulfate
High concentrations of estrone sulfate are found in blood
beginning at about day 80 of pregnancy and in milk from
about day 100 ( Fig. 21-6 ). In a study measuring estrone
sulfate concentrations in milk samples as an indicator
for pregnancy status, an overall accuracy rate of 95%
in milk samples collected at 120 days or later was found
( Henderson et al. , 1994 ) . When comparing peripheral
blood concentrations of estrone sulfate between three
breeds of cattle, it was found that the breed giving birth
to the lightest calves had lower estrone sulfate concentrations
in the interval 101 to 200 days of gestation ( Abdo
et al. , 1991 ). Estrone sulfate measurements cannot be used
to predict time of calving ( Shah et al. , 2006 ) .
3 . Other Substances
Proteins of placental origin, bovine pregnancy-specific
protein B (bPSBP), and bovine pregnancy-associated
glyco-protein 1(bPAG-1) have been observed in the blood
of pregnant cows beginning between days 16 and 21 of
gestation ( Sasser and Ruder, 1987 ). The existence of proteins
that are present only if an embryo is present opens
the way for an early and definitive pregnancy diagnosis in
cattle by blood analysis. Humblot et al. (1988) compared
diagnosis of pregnancy in Frisian cattle by determination
of progesterone and bPSBP in blood. The study revealed
the accuracy (number positive and pregnant/number of
positive diagnoses) of the positive forecast to be 67%
(82/122) for progesterone on day 24 after insemination.
The accuracy of the negative forecast for progesterone
was 98% (52/53). The accuracy of the positive forecast for
bPSPB increased with gestation age from 86% (50/58) on
day 24 to 99% (83/84) on day 70. The accuracy of the negative
diagnoses by bPSPB increased from 72% (84/117) on
day 24 to 100% (83/83) on days 30 to 35. The authors concluded
measurement of bPSPB 30 days after insemination
to be an efficient test both for the positive and the negative
pregnancy diagnoses. A cardinal principle of pregnancy
detection is that the test should be effective by the time the
estrus cycle would end if the animal was not pregnant. This
reemphasizes the main point of early pregnancy detection
(i.e., it is done so the animal can be rebred if not pregnant).
The test fulfilling this criterion has yet to be found.
A comparison of ultrasonography with bPSBP and
bPAG-1 RIA assays showed no difference in accuracy
diagnosis of pregnant cows compared to calving results.
However, the accuracy of detection of nonpregnant cows
by the bPSBP and bPAG-1 measurements was limited by
the relatively long half-life of these proteins after calving
and early embryonic death ( Szenci et al. , 1998 ). On-farm
tests to detect bPAG-1 (early conception factor) have been
developed to be used within 48 h of conception. Although
the test appears to function well, it also has been criticized
for not being reliable for determine nonpregnancy in cattle
( Cordoba et al. , 2001 ).
B . Sheep
1 . Progesterone
Progesterone analysis as an early test for pregnancy has
been used in sheep ( Robertson and Sarda, 1971 ). In the
ewe, the progesterone analysis has to be carried out on
blood samples, as most breeds of sheep are not lactating
at the time of breeding. Maximal luteal phase progesterone
concentrations in the ewe are approximately 2 to 4 ng/ml
(6 to 13 nmol/liter), whereas the concentrations at estrus
range from 0.15 to 0.25 ng/ml (0.5 to 0.8 nmol/liter)
( Stabenfeldt et al. , 1969c ). Using an amplified enzyme