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Endocrine Alterations Associated with Extended Time Interval Between Estrus and Ovulation in High-Yield Dairy Cows

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Short fertile half-lives of the male and female gametes in the female tract necessitate accurate timing of artificial insemination. We examined the possible association between extension of the estrus to ovulation (E-O) interval and alterations in concentrations of estradiol, progesterone, and the preovulatory LH surge before estrus and ovulation. High-yielding Holstein cows (n = 74 from a total of 106) were synchronized and were examined around the time of the subsequent estrus. They were observed continuously for estrual behavior. Blood samples were collected before and after estrus, and ultrasound checks for ovulation were made every 4 h. About three-quarters of the cows exhibited short (but normal) E-O intervals of 22 to 25 h (25%) or normal intervals of 25 to 30 h (47%); 17% of them displayed a long (but normal) E-O interval of 31 to 35 h, and about 10% exhibited a very long E-O interval of 35 to 50 h. Extended E-O interval comprised estrus-to-LH surge and LH surge-to-ovulation intervals that were both longer than normal. Pronounced changes in hormonal concentrations were noted before ovulation in the very long E-O interval group of cows: progesterone and estradiol concentrations were reduced, and the preovulatory LH peak surge was markedly less than in the other 3 groups. Postovulation progesterone concentrations during the midluteal phase were lesser in the very long and the long E-O interval groups compared with those in the short and normal interval groups. Season, parity, milk yield, and body condition did not affect the estrus to LH surge, LH surge to ovulation, and E-O intervals. The results indicate an association between preovulatory-reduced estradiol concentrations and a small preovulatory LH surge, on the one hand, and an extended E-O interval, on the other hand. Delayed ovulation could cause nonoptimal timing of AI, a less than normal preovulatory LH surge that may be associated with suboptimal maturation of the oocyte before ovulation, or reduced progesterone concentrations before and after ovulation. All may be factors associated with poor fertility in cows with a very long E-O interval.
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J. Dairy Sci. 89:4694–4702
© American Dairy Science Association, 2006.
Endocrine Alterations Associated with Extended Time Interval
Between Estrus and Ovulation in High-Yield Dairy Cows
A. Bloch,* Y. Folman,† M. Kaim,† Z. Roth,* R. Braw-Tal,† and D. Wolfenson*
1
*Department of Animal Science, Faculty of Agriculture, The Hebrew University, Rehovot 76100, Israel
†Institute of Animal Science, Agricultural Research Organization, Bet-Dagan 50250, Israel
ABSTRACT
Short fertile half-lives of the male and female ga-
metes in the female tract necessitate accurate timing
of artificial insemination. We examined the possible
association between extension of the estrus to ovulation
(E-O) interval and alterations in concentrations of es-
tradiol, progesterone, and the preovulatory LH surge
before estrus and ovulation. High-yielding Holstein
cows (n = 74 from a total of 106) were synchronized
and were examined around the time of the subsequent
estrus. They were observed continuously for estrual
behavior. Blood samples were collected before and after
estrus, and ultrasound checks for ovulation were made
every 4 h. About three-quarters of the cows exhibited
short (but normal) E-O intervals of 22 to 25 h (25%)
or normal intervals of 25 to 30 h (47%); 17% of them
displayed a long (but normal) E-O interval of 31 to 35
h, and about 10% exhibited a very long E-O interval of
35 to 50 h. Extended E-O interval comprised estrus-
to-LH surge and LH surge-to-ovulation intervals that
were both longer than normal. Pronounced changes in
hormonal concentrations were noted before ovulation
in the very long E-O interval group of cows: progester-
one and estradiol concentrations were reduced, and the
preovulatory LH peak surge was markedly less than
in the other 3 groups. Postovulation progesterone con-
centrations during the midluteal phase were lesser in
the very long and the long E-O interval groups com-
pared with those in the short and normal interval
groups. Season, parity, milk yield, and body condition
did not affect the estrus to LH surge, LH surge to ovula-
tion, and E-O intervals. The results indicate an associa-
tion between preovulatory-reduced estradiol concentra-
tions and a small preovulatory LH surge, on the one
hand, and an extended E-O interval, on the other hand.
Delayed ovulation could cause nonoptimal timing of AI,
a less than normal preovulatory LH surge that may be
associated with suboptimal maturation of the oocyte
Received March 30, 2006.
Accepted June 26, 2006.
1
Corresponding author: wolf@agri.huji.ac.il
4694
before ovulation, or reduced progesterone concentra-
tions before and after ovulation. All may be factors
associated with poor fertility in cows with a very long
E-O interval.
Key words: estrus, ovulation, luteinizing hormone
surge, dairy cow
INTRODUCTION
Delayed ovulation in cows following estrus minimizes
the chances of successful fertilization. The short fertile
half-life of bovine gametes restricts the period during
which fertilization can occur (Dransfield et al., 1998;
Nebel et al., 2000). Fertilization rate of the oocyte de-
creases significantly 8 to 12 h postovulation, and insem-
ination 25 to 40 h before ovulation is associated with
a significant decrease in conception rates (Hunter,
1994). In most studies, mean intervals between onset
of estrus and ovulation (E-O) in beef and dairy cattle
ranged from 23 to 33 h (Renger et al., 1978; Mikeska
and Williams, 1988; Lemaster et al., 1999), and the
mean was reported to be about 27 h in lactating dairy
cows (Walker et al., 1996).
Wide variation among E-O intervals of individual
cows or heifers in older studies was attributed to inade-
quate frequencies of detecting estrus and palpation of
ovaries to determine ovulation. Even in more recent
studies, however, in which modern electronic devices
were used to detect the onset of estrus, and in which
the ovulation time was more frequently monitored by
ultrasonography, a wide variation in E-O intervals was
reported. For example, Walker et al. (1996) reported
that 78% of lactating cows ovulated within 40 h of the
onset of estrus, but that 22% had not ovulated by 40
h. In another recent study of lactating Holstein cows,
a mean E-O interval of 30 h, with a range from 18.5 to
48.5 h was reported (Roelofs et al., 2005). A mean inter-
val of 28 h (ranging from 12 to 36 h) from visual estrus
to ovulation was noted for Bos indicus cows (Cavalieri
et al., 1997). Notably, mean E-O intervals and ranges
were similar for cows exhibiting spontaneous estrus
and for those in which estrus was induced by PGF
2α
(Walker et al., 1996). A wide variation among E-O inter-
vals was recorded for heifers as well; 92% of Holstein
ENDOCRINE CHANGES ASSOCIATED WITH DELAYED OVULATION 4695
heifers ovulated within 36 h of the onset of estrus and
8% between 36 and 48 h after estrus (Hernandez-Ceron
et al., 1993). Lemaster et al. (1999) reported a mean
interval of 26 h and a range from 11 to 71 h in crossbred
Brahman heifers.
Despite extensive documentation over the years that
confirms large variation among E-O intervals of individ-
ual cows, the possible associations between extended
E-O intervals and endocrine traits are poorly docu-
mented. A single study by Saumande and Humblot
(2005) reported a negative correlation between the pre-
ovulatory peak in estradiol concentrations and duration
of the estrus-LH peak and E-O intervals. They hypothe-
sized an ovarian control of those intervals that was
related to a negative correlation between the size of the
preovulatory follicle and the E-O interval. The endo-
crine milieu, however, that is associated with delayed
ovulation and extended E-O interval has not been char-
acterized. The present study characterized groups of
cows that exhibited short, normal, long, or very long E-
O intervals. We focused on the exceptional group of
cows that exhibited a very long E-O interval because a
long E-O interval minimizes the chances of those cows
conceiving. We examined the possibility that the abnor-
mally large E-O interval in a group of high-yielding
cows was associated with alterations in steroid and
gonadotropin concentrations; namely, progesterone
concentrations during the preceding luteal phase, es-
tradiol concentrations before estrus, and LH concentra-
tions at the preovulatory peak.
MATERIALS AND METHODS
Cows
Holstein cows in their first to fifth lactations were
used. The experiment, which was designed with 9 clus-
ters of cows grouped according to their calving dates,
was performed during spring (March to May), summer
(July to August), and fall (October to November). Cows
were kept in an open shed with access to an adjacent
yard. During summer, a sprinkling and ventilation cool-
ing system was used (Flamenbaum et al., 1986). Maxi-
mum and minimum air temperature and relative hu-
midity were as follows: spring, 22.9 and 12.6°C, 67 and
52%; summer, 32.7 and 22.5°C, 69 and 53%; and fall,
27 and 15°C, 68 and 52%, respectively. Cows were fed
ad libitum a TMR containing 1.74 Mcal of NE
L
per kg
of DM and 17% protein. Cows were milked 3 times daily.
Monthly milk yields were recorded, and percentages of
fat and protein were determined by the central labora-
tories of the Israeli Cattle Breeding Association. Body
condition score on a 5-point scale was determined (Wild-
man et al., 1982) by the same person immediately after
calving and at 70 DIM. The experiment was conducted
Journal of Dairy Science Vol. 89 No. 12, 2006
in accordance with the guidelines of the local ethics
committee.
Experimental Protocol
Estrus was synchronized in lactating cows at about
50 to 60 d postpartum by inserting an intravaginal
insert containing progesterone (CIDR, Eazi-Breed,
Hamilton, NZ) for 9 d and treating cows with PGF
2α
analog (Cloprostenol, Estrumate 500 g i.m., Coopers,
Berkhamsted, UK) 2 d before removal of the insert.
To prevent any possible effects of the synchronization
procedure [e.g., the persistent follicle syndrome that
could be induced in cows that receive exogenous proges-
terone in the absence of endogenous corpus luteum (CL;
Smith and Stevenson, 1995)], we began the experimen-
tal examinations during the estrus subsequent to the
synchronized estrus (about 70 to 80 DIM), 3 wk after
terminating the initial estrus-synchronization protocol.
A total of 106 cows (one-third primiparous and two-
thirds multiparous) that had been subjected to the syn-
chronization protocol were observed for estrus 4 times
daily at the time they were expected to manifest estrus.
Cows that were not observed to be in estrus within 4 d
after CIDR removal (during the initial synchronization)
were treated with a single dose of PGF
2α
20 d after CIDR
insert removal. Thus, 2 groups of cows were included in
the experiment: those that manifested estrus following
initial synchronization and those that did not; the latter
were treated with PGF
2α
. A 5-d period of intensive ex-
perimental examinations began 20 d after the synchro-
nized estrus, or 36 h after PGF
2α
. Of the 106 cows sub-
jected to the initial synchronization protocol, 74 cows
(70%) manifested estrus about 3 wk after the initial
protocol within the period of continuous observations
and were included in the study. Of these, 47 cows exhib-
ited spontaneous estrus and 27 exhibited PGF
2α
-in-
duced estrus.
Data Collection
During the experiment, visual indications of estrus
were monitored continuously (24 h daily during 5 d) by
a team of 2 people. Exact onset of estrus was determined
by recording the time of the first standing event, provid-
ing that the individual cow went on to manifest several
standing events and exhibited other behavioral signs
typical of a cow in estrus. Transrectal ultrasonography
of the ovaries was conducted by using a 7.5-MHz probe
(Aloka 210, Tokyo, Japan). It was carried out once at the
beginning of the 5-d period to detect the preovulatory
follicle and to confirm that the ovarian structures were
typical of that found in a normal follicular phase. Com-
mencing 20 h after standing estrus, ultrasonography
BLOCH ET AL.4696
of the ovaries was carried out every 4 h until ovulation
was detected, or until 50 h after the onset of estrus for
cows that failed to ovulate by that time. Based on the
4-h interval of ultrasonographic monitoring, the time
of ovulation was considered to be 2 h before the time
when ovulation could be discerned (Kaim et al., 2003).
From 10 d before expected estrus, blood samples were
collected every other day for progesterone determina-
tion. During the 5-d period of continuous observation,
blood samples for later estradiol determination were
collected every 8 h until the onset of estrus. From the
onset of estrus, samples for LH determination were
collected every 3 h for 24 h. Following ovulation, blood
samples for progesterone determination were collected
every other day fromd1to20ofthecycle.
Hormonal Determinations
Plasma samples for estradiol determination were ex-
tracted with diethyl ether as described previously (Bad-
inga et al., 1992), and extracted samples were analyzed
by RIA as validated in our laboratory (Shaham-Alba-
lancy et al., 2000). The antibody (Diagnostic Products
Corp., Los Angeles, CA) did not cross-react significantly
with other major steroids. Assay sensitivity was 0.5 pg/
mL, and the intra- and interassay coefficients of varia-
tion were 8.5 and 9.5%, respectively. Plasma progester-
one concentrations of unextracted samples were ana-
lyzed by using a solid-phase radioimmunoassay kit (Di-
agnostic Product Corp.) against a standard curve
prepared in our laboratory by dissolving progesterone
in plasma from an ovariectomized cow, as described
previously (Shaham-Albalancy et al., 2000). Assay sen-
sitivity was 0.2 ng/mL and the intra- and interassay
coefficients of variations were 3.9 and 8.6%, respec-
tively. Plasma LH concentrations were measured by
enzyme immunoassay with a biotin-streptavidin ampli-
fication and validated for bovine plasma as described
previously (Mutayoba et al., 1990). The procedure was
validated recently in our laboratory (Kaim et al., 2003).
Intra- and interassay coefficients of variation in the
assay were 8.5 and 10.6%, respectively, and its sensitiv-
ity was 7.8 pg/well. Values for LH are expressed in
nanograms of bovine LH (USDA bLH-B-6) per mil-
liliter.
Data Analyses
Data were analyzed by ANOVA (procedure GLM;
SAS Inst. Inc., Cary NC). Cows were sorted into 4
groups according to the E-O interval range (Figure 1A)
and on the basis of previous publications, as follows:
The first group, with intervals between 22 and 25 h,
was designated as having a short (but normal) interval
Journal of Dairy Science Vol. 89 No. 12, 2006
(Figure 1B). The second group, with an E-O interval of
26 to 30 h (most common range reported in the litera-
ture), was designated as normal (Walker et al., 1996;
Rajamahendran et al., 1998, Roelofs et al., 2005). The
third group comprised cows having E-O intervals be-
tween 31 and 35 h; this range was considered long (but
normal), and the group was designated as having a long
interval. Finally, a fourth group of cows with an E-O
interval greater than 36 h was designated as having a
very long interval (Figure 1B). Sorting the experimental
cows into 4 groups according to the E-O interval range
enabled us to efficiently characterize the extended E-
O interval syndrome. This syndrome has been described
(Walker et al., 1996), but little is known about its endo-
crine characteristics. This syndrome was represented
in the present study by the group of cows with a very
long E-O interval. We tested the effects of the type of
estrus (spontaneous or PGF
2α
-induced) on the distribu-
tion of cows among the 4 groups, and on hormone (estra-
diol, progesterone, and LH) concentrations. On the ba-
sis of these analyses, type of estrus was ignored in
subsequent analyses because it had no significant effect
on any outcome of interest, and the results for cows
exhibiting the 2 types of estrus were combined, as in
studies by other workers (Walker et al., 1996). Data
related to intervals from estrus to the LH surge, the
LH surge to ovulation, and the E-O intervals, peak
concentration of the LH surge, milk yield and composi-
tion, and BCS were analyzed by one-way ANOVA. Ef-
fects of season and parity on distribution of cows among
the 4 E-O interval groups was tested by χ
2
. The statisti-
cal models for hormonal concentrations included the
effects of E-O interval groups, cows (within a group),
time (hours or days from estrus), milk yield, body condi-
tion, parity, and season.
RESULTS
Length and Distribution of Intervals Between
Estrus, LH Surge, and Ovulation
Distribution of the E-O interval ranged from 22 to at
least 50 h (Figure 1A). The group having normal E-O
intervals (26 to 30 h) comprised about half (47%) of the
examined cows (Figure 1B). The group with short E-O
interval (22 to 25 h) comprised 25% of the cows. These
2 groups taken together represented nearly three-quar-
ters of the cows that exhibited short or normal E-O
intervals of 22 to 30 h. The group with long E-O inter-
vals (31 to 35 h) comprised 17% of the cows. The fourth
group with very long E-O intervals (>36 h) comprised
7 cows (i.e., 10% of the experimental cow population
examined in this study). Three cows of this group failed
to ovulate by 50 h after the onset of estrus (scanning
ENDOCRINE CHANGES ASSOCIATED WITH DELAYED OVULATION 4697
Figure 1. A) Distribution of the experimental cow population (n = 74) sorted by estrus to ovulation intervals. Individual values are
subject to an estimated error of ±2 h. B) Distribution (%) of the experimental cow population among 4 groups of cows, sorted according to
their range of estrus-ovulation interval into short, normal, long, and very long intervals.
was not continued after 50 h), and these 3 cows were
designated as having an E-O interval of at least 50 h.
Further evaluation of these 3 cows clearly indicated
that each eventually ovulated and subsequently devel-
oped a CL. First, ultrasound examinations performed
twice, at about 8 to 10 d and 13 to 15 d after estrus,
indicated that in all 3 cows, the largest follicle disap-
peared and a new, normal-size CL was present in the
expected ovary. These CL were much larger than the
average size (about 17 mm in diameter) of correspond-
ing ovulatory follicles, and their average calculated vol-
ume (about 7,300 mm
3
) was within normal range for
CL at that stage of the cycle. Second, progesterone con-
centrations in 2 of these cows exhibited a normal post-
ovulatory pattern that did not differ from those shown
in Figure 3. In the third cow, the progesterone pattern of
increase was similar, but was delayed by 4 d. Individual
midluteal-phase concentrations of progesterone of the
3 cows were 4.8, 5.1, and 7.5 ng/mL. They were typical
and within the normal range for high-yielding cows and
were indicative of steroidogenically active CL. Collec-
tively, these findings confirmed that the 3 cows that
failed to ovulate by 50 h after the onset of estrus did
so eventually.
The mean interval between the onset of estrus and
the peak LH surge was later (P < 0.01) at9hinthe
very long E-O interval group, compared with 3.5 h in
the normal interval group (Table 1). Interval from the
LH surge to ovulation was greater (P < 0.01) by about
4 h in the long and very long groups than in the normal
group (Table 1).
Journal of Dairy Science Vol. 89 No. 12, 2006
Milk, milk fat, and protein yields during the experi-
mental period did not differ among the 4 experimental
groups (Table 2). Similarly, BCS at calving or during
the experimental period (70 DIM) did not differ among
the 4 experimental groups (Table 2). Effects of season
on distribution of cows among the 4 E-O interval groups
were minor and not statistically significant. Likewise,
we did not find any significant effect of parity on distri-
bution of cows among E-O interval groups (neither pri-
miparous compared with multiparous cows, nor com-
parisons among multiparous cows with differing num-
bers of lactations had any effect on the above). It is
noteworthy that the time of onset of estrus (day or
night) did not have any significant effect on the E-O in-
terval.
Ultrasound examination of the ovaries at the begin-
ning of the 5-d period of intensive experimental exami-
nations indicated that, similar to experimental cows
with a normal E-O interval, the ovaries of the cows with
a very long E-O interval exhibited a normal appearance,
typical of the follicular phase, consisting of 1 or 2 large
follicle(s), a few medium-size follicles, and a regressing
CL. Likewise, later ultrasound examinations (during
the 5-d period, intended to determine the time of ovula-
tion) confirmed the presence of a dominant follicle and a
CL in an advanced stage of regression. All experimental
cows ovulated, as indicated by the growth of new CL
and elevated concentrations of plasma progesterone.
Proportions of cows having spontaneous or induced es-
trus (63 and 36%, respectively) were similar in the
short, normal, long, and very long E-O interval groups.
BLOCH ET AL.4698
Table 1. Intervals between estrus and LH surge, LH surge and ovulation, and estrus and ovulation in the
4 groups of cows, sorted by range of intervals between estrus and ovulation (mean ± SE)
Interval from estrus to ovulation groups
Short Normal Long Very long Overall
Estrus to LH surge, h 0.0 ± 0.6
a
3.5 ± 0.5
b
3.9 ± 0.8
b
9.0 ± 3.5
c
2.8 ± 0.4
LH surge to ovulation, h 24.0 ± 0.5
a
24.7 ± 0.5
a
28.4 ± 0.8
b
28.2 ± 3.2
b
25.5 ± 0.5
Estrus to ovulation, h 23.9 ± 0.2
a
28.2 ± 0.2
b
32.3 ± 0.4
c
42.6 ± 2.6
d
28.6 ± 0.6
a–d
Means of the 4 interval groups within a row having different superscript letters differ (P < 0.01).
Among the last group, 4 and 3 of 7 cows (57 and 42%,
respectively) exhibited natural and induced estrus, re-
spectively.
Hormonal Concentrations
A weak correlation was detected between the E-O
interval and mean progesterone concentration during
the 10-d period before the examined estrus (r = 0.27;
P < 0.04). Correlations between the E-O interval and
peak estradiol concentration before estrus (r = 0.17;
P < 0.15) or peak LH surge concentration (r = 0.21;
P < 0.09) were slight and not statistically significant.
Further analyses, described below, were applied after
the experimental cows had been sorted into 4 groups
according to their E-O interval range.
Progesterone concentrations before the examined es-
trus are presented in Figure 2. The very long interval
group exhibited reduced (P < 0.05) progesterone concen-
trations during the 10-d period before estrus than those
in the short, normal, and long groups (2.8 ± 0.6 vs. 4.2
± 0.2 ng/mL; pooled value for the latter 3 groups). Luteal
regression in the very long interval group started ear-
lier than in the other 3 groups, as manifested in the
decline in progesterone on d 5 rather than on d 3
(Figure 2). As in the cycle preceding ovulation, proges-
terone concentration curves during the midluteal phase
of the cycle following the examined ovulation (d 11 to
18; Figure 3) were less (P < 0.04) in the very long inter-
Table 2. Milk and milk component yields during the experimental period, BCS, and cycle durations of the
4 groups of experimental cows, sorted by range of intervals between estrus and ovulation (mean ± SE)
1
Interval from estrus to ovulation groups
Short Normal Long Very long
Milk yield, kg/d 47.1 ± 2.8 43.9 ± 1.4 44.7 ± 2.3 47.1 ± 3.5
Milk fat, kg/d
2
1.51 ± 0.11 1.55 ± 0.06 1.46 ± 0.11 1.67 ± 0.17
Milk protein, kg/d
2
1.35 ± 0.08 1.29 ± 0.03 1.30 ± 0.07 1.38 ± 0.08
BCS at calving 3.3 ± 0.1 3.1 ± 0.1 3.2 ± 0.1 3.3 ± 0.2
BCS at 70 DIM 2.6 ± 0.1 2.5 ± 0.1 2.5 ± 0.1 2.4 ± 0.1
Estrous cycle length, d 22.0 ± 0.6 21.6 ± 0.4 22.2 ± 0.5 22.3 ± 0.8
1
Means did not differ among the 4 groups of cows.
2
Mean percentages of milk fat and milk protein were 3.40 ± 0.06% and 2.92 ± 0.02%, respectively.
Journal of Dairy Science Vol. 89 No. 12, 2006
val group, and also in the long interval group, than in
the short or normal groups (4.4 vs. 5.6 ng/mL). As in
the preceding cycle, luteolysis started earlier in the
groups with longer intervals than in those with short
or normal intervals (Figure 3). Cycle durations were
similar in the 4 groups of cows (Table 2).
Concentrations of estradiol during the follicular
phase before the LH surge were less (P < 0.06) in the
very long interval group than in the other 3 groups
(Figure 4). Interestingly, mean diameters of the preovu-
latory follicles on the day before ovulation did not differ
between the short, normal, long, and very long interval
groups (16.8 ± 0.6, 17.0 ± 0.3, 16.3 ± 0.6, and 17.7 ± 0.5
mm, respectively).
Concentrations of LH at the time of the preovulatory
surge were normalized to the peak concentration of the
LH surge in each of the 4 groups of cows. As shown in
Figure 5, the peak of LH surge concentration in the
very long interval group was about 2.5 times less (P <
0.03) than those in the other 3 groups. Mean peak LH
surge concentration in the short, normal, and long
groups was 10 ng/mL, with no significant difference
among them, and that in the very long interval group
was 4 ng/mL (Figure 5).
DISCUSSION
Short fertile half lives of the oocyte after ovulation
and of the spermatozoa in the female tract (Hunter,
ENDOCRINE CHANGES ASSOCIATED WITH DELAYED OVULATION 4699
Figure 2. Concentrations of plasma progesterone in the 4 groups
of cows sorted by estrus-ovulation (E-O) interval during 10 d before
estrus. Concentrations in the very long E-O interval group were less
(P < 0.03) than in the other groups before estrus. Pooled SEM = 0.73.
1994) narrow the optimal time window for maximal
fertilization. In the present study, we characterized an
abnormal group of cows that exhibited delayed ovula-
tion and an extended E-O interval. This group formed
one-tenth of the total number of cows. The present study
sheds light on changes in the endocrine milieu that
may be partly associated with reduced fertility in cows
having extended E-O intervals. These changes included
low concentrations of progesterone and estradiol and a
low LH surge before ovulation.
The proportion of cows found to exhibit an extended
E-O interval varies among studies. In the present
study, the very long interval group comprised 10% of
Figure 3. Concentrations of plasma progesterone in the 4 groups
of cows sorted by estrus-ovulation (E-O) interval during the cycle
following ovulation. Data were normalized according to time of ovula-
tion. Concentrations in long and very long E-O interval groups during
midluteal phase were less (P < 0.04) than in the other groups. Pooled
SEM = 0.69.
Journal of Dairy Science Vol. 89 No. 12, 2006
Figure 4. Concentrations of plasma estradiol before ovulation
in the 4 groups of cows sorted by estrus-ovulation (E-O) interval.
Concentrations in the very long E-O interval group were less (P <
0.06) than in the other groups. Pooled SEM = 0.49.
the experimental cows, whereas in earlier studies it
ranged from 8% in heifers (Hernandez-Ceron et al.,
1993) to 15 to 22% in cows (Walker et al., 1996; Roelofs
et al., 2005). The number of cows used in the present
study provided a sufficiently large study population to
support adequate statistical analyses. Continuous ob-
servation for estrus and frequent ultrasonographic
monitoring enabled us to accurately determine the time
of ovulation and the E-O interval for each cow, with an
estimated error of ±2 h. In this respect, repeated rectal
ultrasound examinations of dairy cows (as performed
herein for determination of ovulation) did not alter the
timing of estrus, durations of the E-O, and estrus to
Figure 5. Concentrations of plasma preovulatory LH surges in
the 4 groups of cows sorted by estrus to ovulation (E-O) interval.
Data were normalized according to peak LH in each group and are
presented relative to the onset of estrus. Concentration of peak LH
in the very-long E-O interval group was less (P < 0.01) than in the
other groups. Pooled SEM = 0.68.
BLOCH ET AL.4700
LH surge intervals, or the periovulatory concentrations
of plasma steroids and LH (Roelofs et al., 2004).
The present study provides clear evidence that an
extended E-O interval is associated with alterations in
the concentrations of progesterone, estradiol, and LH
surge in plasma. We found markedly different hor-
monal profiles in the extended E-O interval (very long
E-O) group of cows than in the other 3 “normal” groups
of cows. Saumande and Humblot (2005) found correla-
tions between the preovulatory estradiol concentra-
tions, the preovulatory follicle size, and the E-O inter-
val. The present study, however, indicated that alter-
ations in progesterone, estradiol, and LH surge
concentrations before ovulation were evident only in
cows with an extended E-O interval and not in the
entire population of experimental cows. Although pre-
ovulatory follicle size in the very long E-O interval
group did not differ from that in the normal interval
groups, the reduced estradiol concentrations found in
the former group were presumably due to development
of a less steroidogenically active, preovulatory follicle.
Reduced estradiol concentrations before estrus proba-
bly delayed the LH surge so that the estrus to LH surge
interval was about 6 h longer in the very long interval
group than in the normal interval group. Although it
is generally accepted that most of the variation in the
E-O interval can be attributed to variation in the estrus
to LH surge interval (Saumande and Humblot, 2005),
the present findings indicate that extension of the inter-
val from LH surge to ovulation also contributed to
that variation.
The markedly small preovulatory LH surge ampli-
tude in the very long E-O group, which is reported for
the first time in our study, could be related to low pre-
ovulatory estradiol concentrations. Indeed, we found a
close association between low preovulatory estradiol
concentrations and low-amplitude LH surges, which
occurred only in the group of cows with a very long E-
O interval, and not among the entire population of cows.
A less-than-normal LH surge peak could be associated
with a delayed timing of ovulation, which caused, in
turn, a significant 4-h extension of the LH surge to
ovulation interval in the very long E-O interval group.
This interpretation is strengthened by findings that
induction of stress in sheep or cows by endotoxin (LPS)
administration during the follicular phase or at the
onset of estrus was associated with a decline in the LH
surge amplitude and with delayed ovulation (Battaglia
et al., 1999; Suzuki et al., 2001; Lavon et al., 2004). It
should be mentioned, however, that a similar extension
of the LH surge to ovulation interval also was noted in
the long E-O interval group. Collectively, the present
findings suggest that extension of the E-O interval is
probably associated with 1) delayed secretion of the
Journal of Dairy Science Vol. 89 No. 12, 2006
preovulatory LH surge relative to onset of estrus, possi-
bly because of inadequate concentrations of estradiol;
and 2) extension of the time between the LH surge and
the occurrence of ovulation, possibly because of limited
secretion during the preovulatory LH surge.
Luteal insufficiency in cows with a very long E-O
interval, which is reported here for the first time, is
characterized not only by low progesterone concentra-
tion curves, but also by an earlier luteal regression
before estrus. The reason for this insufficiency is not
yet clear. Interestingly, the reduced luteal progesterone
concentration curve does not seem to be a random event
because this pattern was repeated in the next cycle
after ovulation. Low progesterone curves could result
from low estradiol concentrations and a consequently
smaller LH surge, which could be associated with sub-
optimal luteinization of the growing CL after ovulation.
This relationship has been found in primates (Zelinski-
Wooten et al., 1997). Studies in cows (Ambrose et al.,
1998; Less et al., 1998; Rajamahendran et al., 1998)
showed that an induced small LH surge was associated
with inadequate postovulation plasma progesterone
concentrations. Likewise, granulosa cells that were ex-
posed to an inadequate or short-lived LH surge at the
beginning of culture secreted less progesterone at the
end of luteinization (Biger et al., 2000). An alternative
reason for suboptimal progesterone secretion in these
cows does not necessarily involve a small LH surge. A
suboptimal CL could result from ovulation of a subopti-
mal preovulatory follicle, as indicated by the reduced
concentrations of estradiol during the follicular phase
in those cows. This hypothesis is supported by previous
findings that a less-well-developed preovulatory follicle
yielded a poor progesterone-secreting CL (Vasconcelos
et al., 1999), and also that heat-stress–impaired follicles
yielded poor progesterone-secreting CL (Wolfenson et
al., 2002).
The likelihood that cows having the very long E-O
intervals will conceive seems improbable for several
reasons. First, as mentioned previously, the weaker
association between time of AI and time of ovulation
minimizes the probability of successful fertilization.
Second, a small preovulatory LH surge may impair the
normal process of resumption of meiosis and nuclear
maturation (Tsafriri et al., 2005), and therefore could
lead to development of an incompetent oocyte before
ovulation. Third, cows with a long E-O interval exhib-
ited low progesterone concentration curves, both before
and after ovulation, which occasionally have been found
to be associated with poor fertility (Kimura et al., 1987;
Folman et al., 1990). These points are supported by a
recent study (Kaim et al., 2003) in which lactating cows
treated with GnRH at onset of estrus exhibited im-
proved fertility. Greater conception was associated with
ENDOCRINE CHANGES ASSOCIATED WITH DELAYED OVULATION 4701
induction of a shorter, less variable E-O interval, as
well as with elevated postovulatory concentrations of
circulating progesterone.
In conclusion, a group of cows with an extended E-
O interval was characterized by reduced concentrations
of estradiol and a small LH surge before ovulation, and
by low concentrations of progesterone before and after
ovulation. The extended interval between estrus and
ovulation, and the depressed hormonal secretions prob-
ably minimize the likelihood that these cows could con-
ceive. No simple means exists presently to identify this
group of cows that have an extended E-O interval.
Therefore, hormonal treatments of cows having an ex-
tended E-O interval, intended to improve specifically
their fertility, rather than general treatment of the
whole herd, are currently not applicable to commercial
herds, and further research is needed to achieve a suit-
able treatment. Such treatments include administra-
tion of GnRH at onset of estrus, or delaying the applica-
tion of AI relative to time of estrus.
ACKNOWLEDGMENTS
The authors express their appreciation of the help
given by the staff of the dairy farm in Kibbutz Naan,
Israel, and to the USDA for the provision of bovine LH
and bovine LH antibodies.
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... This is because sperm lifespan after injection into the genital tract is limited [4], and the sperm needs to fertilize an oocyte before its lifespan ends. It has been reported that the interval from the onset and end of estrus to ovulation is 27-30 h [5][6][7][8][9] and 12-19 h [5, 7, 8], respectively, and the duration of estrus (from the onset to the end of estrus) is 7-16 h [5,6,8,10]. The optimal AI timing for high pregnancy rates was 5-16 h from the onset of estrus using conventional semen [11] and 23-41 h [12] and 16-24 h [13] using sex-sorted semen. ...
... The optimal AI timing for high pregnancy rates was 5-16 h from the onset of estrus using conventional semen [11] and 23-41 h [12] and 16-24 h [13] using sex-sorted semen. One of the challenges in considering the optimal AI timing is the large variation in the interval from the onset of estrus to ovulation [9]. When estrus continues for a certain period (e.g., 24 h) from the first AI, the second AI is commonly decided by herdsmen [14,15] to ensure that the animal is inseminated at the optimal timing in relation to ovulation; thus, the time of the end of estrus is occasionally used as a reference for the second AI implementation in the field. ...
... In contrast, other studies using the Jersey breed indicated that pregnancy rates were highest at 23-41 h [12] and 16-24 h [13] from the onset of estrus detected by the accelerometer and a pressure sensor system, respectively. The reason why the time of the onset of estrus did not indicate the optimal AI timing in the present study was the potentially large variation in the interval from the onset of estrus to ovulation [9] compared with that from the end of estrus to ovulation. The large variation in estrus duration from 8 to 28 h observed in the present study, which is consistent with previous findings [8,16], supports this explanation. ...
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... In this process, FSH stimulates the follicular growth, development, and function, while LH causes the follicle to rupture and the corpus luteum to develop. Several research articles have indicated endocrine impairment in estrogen (E 2 ), progesterone (P 4 ), or luteinizing hormone (LH) as the potential reasons for the repeat breeding problem [5][6][7]. In addition, usual levels of various biochemical constituents are indispensable for regular function of various systems of the body. ...
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... Additionally, the administration of buserelin, a GnRH analog, at the time of AI has also been reported not to affect the interval from the onset of estrus to ovulation (Ryan et al., 1994). The administration of GnRH is a direct link to ovulation due to its effects on LH secretion and pulse frequency (Bloch et al., 2006). Administration of GnRH at the onset of estrus in previous studies was found to increase the intensity (both the amplitude and the area under the curve) of the preovulatory LH surge and shorten the interval from the onset of estrus to the LH surge and subsequently ovulation (Kaim et al., 2003). ...
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Cows with reduced estrous expression have compromised fertility. The aim of this study was to determine whether the administration of GnRH at the time of artificial insemination (AI) would affect ovulation rates and the fertility of animals expressing estrous behavior of lesser intensity. Cows were enrolled at the time of estrus from 3 farms (n = 2,607 estrus events; farm A: 1,507, farm B: 429, farm C: 671) and randomly assigned to receive GnRH at AI or not (control). The intensity of estrous expression, monitored through leg-mounted activity monitors, was determined using the maximum activity during estrus; estrous expression was categorized as greater or lower relative to the farm median. On farm A, cows were assessed at alert, and 24 h, 48 h, and 7 d post-alert for ovulation using ultrasonography. Pregnancy per AI was confirmed at 35 ± 7 d post-estrus for cows that were inseminated. Differences between treatments were tested using the GLIMMIX procedure of SAS. Treatment with GnRH at the time of AI increased pregnancy per AI (41.3 ± 1.6 vs. 35.7 ± 1.7%). An interaction between treatment and estrous expression on pregnancy per AI was found. Control cows with greater estrous expression had greater pregnancy per AI than those with lesser expression, whereas GnRH administration increased pregnancy per AI for cows with lesser estrous expression but not those with greater expression (GnRH, greater intensity: 43.5 ± 2.1; GnRH, lesser intensity: 37.8 ± 2.2; control, greater intensity: 42.6 ± 2.2; control, lesser intensity: 31.0 ± 2.2%). A higher proportion of cows with greater estrous expression that were administered GnRH at AI were found to ovulate by 48 h and 7 d post-estrus; however, ovulation of cows with lesser estrous expression was unaffected by GnRH administration. In conclusion, fertility of cows with reduced estrous expression may be increased using GnRH at the time of AI; however, increased ovulation rates do not seem to be the direct mechanism behind this relationship.
... Mastitis may also interfere with corpus luteum regression, progesterone secretion, and endometrial functions (Gilbert et al., 1990;Mann and Lamming, 2001;Spencer et al., 2004). Furthermore, low magnitude of LH surge has been shown to be associated with impaired luteinization of the corpus luteum and low circulating progesterone after ovulation and insemination, which may be associated with low embryo survival and increase in services per conception (Zelinski-Wooten et al., 1997;Bloch et al., 2006). The exact mechanisms by which mastitis is associated with suppression of fertility have yet to be resolved. ...
Article
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Compared with clinical mastitis, the subclinical form of mastitis (SCM) is more common and thought to cause more economic losses to the dairy industry. The current study aimed to investigate the prevalence, risk factors of SCM, and effects on reproduction of dairy cows in major milk-producing areas of Sri Lanka. A total of 1,357 cows of selected farms in 3 regions were examined in the study. California Mastitis Test was conducted for individual cows, and a score of 2 or more for any quarter without any clinical symptoms and abnormalities in milk was considered as positive for SCM. Samples from infected animals were collected and subjected to bacteriological analysis. A pretested questionnaire was used to collect data on individual cows and herds. Risk factors associated with SCM were analyzed using binary logistic regression in generalized linear mixed models. The effect of SCM on calving to conception interval and days from calving to artificial insemination were analyzed by survival analysis using Cox's proportional hazards regression and Kaplan-Meier survival function estimates, respectively. A Poisson regression model was run to determine the effect of SCM on number of artificial inseminations per conception. The prevalence of SCM was 57.5, 11.8, and 45.5% in the regions A, B, and C, respectively. The most common pathogen was Staphylococcus aureus, with 87.1, 56.5, and 92.3% in the regions A, B, and C, respectively. Logistic regression analysis showed that parity, farming system, milking area, region, and herd significantly affect the prevalence of SCM. Subclinical mastitis during the pre-breeding period was associated with 14% increase in the chance of having a greater number of artificial inseminations per conception. Likewise, median days from calving to artificial insemination was longer in cows with SCM compared with normal cows (79 and 64 d, respectively). Therefore, SCM affected the inseminated proportion of studied cows. However, SCM was not associated with the calving to conception interval. The results revealed that the cow factors and milk hygiene play a significant role in the prevalence of SCM.
... Among the major functional causes, hormonal insufficiency and dysfunction contribute about 40.1% cases of repeat breeding. There is altered levels of hormones such as estrogen, progesterone, luteinizing hormone (LH) in repeat breeders associated with prolonged estrus and extended estrus-to-ovulation interval (Bage et al., 2002;Bloch et al., 2006). Approximately 30-40 % of the total numbers of repeat breeding cattle showed prolonged estrus (37-60 vs. 24-36 hours) and 70 % recorded marginally elevated progesterone levels (0.3 to 0.35 ng/ml) during or around estrus (Singh et al., 2012) In repeat breeder cattle with prolonged estrus, the use of single insemination along with administration of GnRH analogue, is sufficient, however, in the absence of hormonal treatment, delayed insemination (Villarroel and Lane, 2010) or double insemination at 24 h interval (Sharma et al., 2006) also gives optimal results. ...
Article
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The present study was conducted to determine the hormonal profile and fertility response in prolonged estrus affected repeat breeder crossbred cows by using modified ovsynch protocol. Total 20 crossbred cows, not conceiving even after more than four services were selected from the semi-arid area of Banaskantha district in Gujarat. They were divided into two equal groups: Group-I (n=10)-cows with prolonged estrus period (> 28 hrs) and Group-II (n = 10)-cows with normal estrus period (18 to 28 hrs). The animals of both groups were treated with modified ovsynch protocol using double dose of GnRH (@ 20 μg) starting from 5 th day of estrous cycle. The blood was collected on day 0, 7 th , 9 th and 25 th (15 th day post-FTAI) of the treatment for determination of plasma progesterone and estradiol hormones. The conception rates in group I and II were 60 and 70%, respectively. The cows with prolonged estrus had non-significantly higher mean plasma progesterone (3.51 ± 0.45 vs 2.97 ± 0.38 ng/ml) and lower estradiol (44.36 ± 1.74 vs 54.56 ± 2.49 pg/ml) as compared to normal estrus cows on day 0 of protocol. The progesterone levels were significantly (p < 0.05) higher on day 7 th (day of PG injection) and 9 th (day of second GnRH injection) of protocol in prolonged estrus cows than normal estrus group. The plasma estradiol concentration was significantly (p < 0.05) lower at all the periods in prolonged estrus cows than those of normal estrus group, except on 25 th day. In repeat breeding cows with prolonged estrus, the plasma progesterone concentration was significantly higher on day 25 (day 15 post-AI) of treatment in conceived as compared to non-conceived cows, whereas in normal estrus cows, there was no significant difference. While, estradiol concentration was significantly lower in conceived than non-conceived cows in both the groups.
... Thus, it is possible that GnRH administration shortly after OE improves the timing and amplitude of the LH surge, thereby leading to ovulation, resumption of meiosis of the ovulated oocyte and increased fertilization rate. In addition, GnRH-induced normal LH surge may improve normal CL formation and progesterone secretion [30], which is important in supporting the formed embryo. ...
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We examined gonadotropin-releasing hormone (GnRH) administration at onset of estrus (OE), determined by automatic activity monitoring (AAM), to improve fertility of dairy cows during the summer and autumn. The study was performed on two dairy farms in Israel. The OE was determined by AAM recorded every 2 h, and a single im dose of GnRH analogue was administered shortly after OE. Pregnancy was determined by transrectal palpation, 40 to 45 d after artificial insemination (AI). Conception risk was analyzed by the GLIMMIX procedure of SAS. Brief visual observation of behavioral estrus indicated that about three-quarters of the events (n = 40) of visually detected OE occurred within 6 h of AAM-detected OE. Accordingly, the GnRH analogue was administered within 5 h of AAM-detected OE, to overlap with the expected endogenous preovulatory LH surge. Overall, pregnancy per AI (P/AI) was monitored over the entire experimental period (summer and autumn) in 233 first, second or third AI (116 and 117 AI for treated and control groups, respectively). Least square means of P/AI for treated (45.8%) and control (39.4%) groups did not differ, but group-by-season interaction tended to differ (p = 0.07), indicating no effect of treatment in the summer and a marked effect of GnRH treatment (n = 58 AI) compared to controls (n = 59 AI) on P/AI in the autumn (56.6% vs. 28.5%, p < 0.03). During the autumn, GnRH-treated mature cows (second or more lactations), and postpartum cows exhibiting metabolic and uterine diseases, tended to have much larger P/AI than their control counterparts (p = 0.07–0.08). No effect of treatment was recorded in the autumn in first parity cows or in uninfected, healthy cows. In conclusion, administration of GnRH within 5 h of AAM-determined OE improved conception risk in cows during the autumn, particularly in those exhibiting uterine or metabolic diseases postpartum and in mature cows. Incorporation of the proposed GnRH treatment shortly after AAM-detected OE into a synchronization program is suggested, to improve fertility of positively responding subpopulations of cows.
... Several studies have indicated the endocrine impairment in progesterone, estrogen and luteinizing hormone levels as putative cause for the repeat breeding in cows (Bage et al., 2002, Saumande and Humbolt, 2005, Bloch et al., 2006. Sustained adrenal stimulation associated with environmental or social stress could be one of the factors that contribute to these hormonal imbalances in repeat breeders (Bage et al., 2000). ...
Article
Background: The effect of systemic cortisol on pregnancy rate during early pregnancy in repeat breeding cows was estimated.Methods: Oestrus synchronisation was done in 20 repeat breeders and samples were collected on different days of post-insemination to estimate cortisol.Result: Trans-rectal ultrasonography on 26th day of post insemination revealed a pregnancy rate of 45%. When two groups were compared, serum, salivary and urinary cortisol level of non-pregnant animals were significantly (P less than 0.05) increased than that of pregnant animals on different days of post-insemination. Within non-pregnant animals, serum, salivary and urinary cortisol levels showed a significant (P less than 0.05) variation between different days of post insemination, but this variation was not observed in pregnant animals. Spearman rho correlation revealed positive association (P less than 0.05) of systemic cortisol with pregnancy rate. In non-pregnant animals, salivary and urinary cortisol levels were observed to be positively correlated (P less than 0.05) with serum cortisol. The results indicate that systemic cortisol has influence on pregnancy rate in repeat breeding cows, this may be due to its effect on embryo implantation and hormonal balance, which requires further validation. Association of salivary and urinary cortisol with serum cortisol indicates their use as non-invasive samples to monitor the hypothalamic-pituitary-adrenal axis activity in repeat breeders.
... This means that it may be more effective to use semen from some sires when cows are inseminated after detected oestrus, and from others when FTAI is used. The probability of getting pregnant is related to the relative time between the insemination and ovulation(Hockey et al., 2010), but the interval from oestrus to ovulation varies widely among different cows(Bloch et al., 2006;Hockey et al., 2010).Valenza et al. (2012) reported that even when using electronic devices to detect individual activities, ~25% of the cows were inseminated too early and ~ 20% too late. Both, semen lifespan and oocyte time viability interact to determine the final fertility(Gosálvez et al., 2011;Hockey et al., 2010). ...
Article
The first aim of this study was to determine the influence of the procedures [(hormonal treatments for fixed time artificial insemination (FTAI) vs insemination at spontaneous estrus (SEAI)] on several inseminations. A second aim was to determine the influence of some intrinsic and extrinsic factors and their interactions, including characteristics of the animals such as age, season, farm, sire, and AI technician on the response to both procedures. A retrospective analysis was performed from a data base of 120.807 inseminations of healthy cows with at least 40‐70 days post‐partum at first service. Overall, FTAI achieves slighter greater pregnancy rates than insemination after detected estrus. The second seems to be a key insemination as effects of sire and technician were greater than in the following inseminations. The use of FTAI or SEAI in one AI did not affect the results of the following services regardless if FTAI or SEAI procedures were used in that AI. Technician had greater variation than sire or farm on final pregnancy rate. The results of each sire for pregnancy rate varied according to the type of insemination, with sires achieving greater results with one or other procedure. Pregnancy rate was positively related to the days in milk in the first two AI. Results were greater in autumn than in spring services.
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To examine endocrine and biochemical differences between dominant and subordinate follicles and how the dominant follicle affects the hypothalamic-pituitary-ovarian axis in Holstein cows, the ovary bearing the dominant follicle was unilaterally removed on Day 5 (n = 8), 8 (n = 8), or 12 (n = 8) of synchronized estrous cycles. Follicular development was followed daily by ultrasonography from the day of detected estrus (Day 0) until 5 days after ovariectomy. Aromatase activity and steroid concentrations in first-wave dominant and subordinate follicles were measured. Intact dominant and subordinate follicles were cultured in 4 ml Minimum Essential Medium supplemented with 100 microCi 3H-leucine to evaluate de novo protein synthesis. Five days after unilateral ovariectomy, cows were resynchronized and the experiment was repeated. Follicular growth was characterized by the development of single large dominant follicles, which was associated with suppression of other follicles. Concentrations of estradiol-17 beta (E2) in follicular fluid and aromatase activity of follicular walls were higher in dominant follicles (438.9 +/- 45.5 ng/ml; 875.4 +/- 68.2 pg E2/follicle) compared to subordinate follicles (40.6 +/- 69.4 ng/ml; 99.4 +/- 104.2 pg E2/follicle). Aromatase activity in first-wave dominant follicles was higher at Days 5 (1147.1 +/- 118.1 pg E2/follicle) and 8 (1028.2 +/- 118.1 pg E2/follicle) compared to Day 12 (450.7 +/- 118.1 pg E2/follicle). Concentrations of E2 and androstenedione in first-wave dominant follicles were higher at Day 5 (983.2 +/- 78.2 and 89.5 +/- 15.7 ng/ml) compared to Days 8 (225.1 +/- 78.6 and 5.9 +/- 14.8 ng/ml) and 12 (108.5 +/- 78.6 and 13.0 +/- 14.8 ng/ml). Concentrations of progesterone in subordinate follicles increased linearly between Days 5 and 12 of the estrous cycle. Plasma concentrations of FSH increased from 17.9 +/- 1.4 to 32.5 +/- 1.4 ng/ml between 0 and 32 h following unilateral removal of the ovary with the first-wave dominant follicle. Increases in plasma FSH were associated with increased numbers of class 1 (3-4 mm) follicles in cows that were ovariectomized at Day 5 or 8 of the cycle. Unilateral ovariectomy had no effects on plasma concentrations of LH when a CL was present on the remaining ovary. First-wave dominant follicles incorporated more 3H-leucine into macromolecules and secreted high (90,000-120,000) and low (20,000-23,000) molecular weight proteins that were not as evident for subordinate follicles at Days 8 and 12.(ABSTRACT TRUNCATED AT 400 WORDS)
Article
Our objective was to examine the role of progestin type on serum concentrations of progesterone (P 4 ) and estradiol-17β (E 2 ), ovarian follicular dynamics, and fertility in cattle in the presence or absence of a corpus luteum (CL) in an estrus synchronization scheme using progestin and PGF 2α . In Exp. 1, 325 cows and heifers were given one injection of PGF 2α (d 0) and then assigned randomly within parity to five treatments : to receive a second PGF 2α injection 14 d later (control) ; to receive norgestomet (NORG) for 7 d beginning on d 8, with a second PGF 2α injection given either 1 d (NORG + no CL) or 6 d (NORG + CL) after insertion ; or to receive a P 4 -releasing intravaginal device (PRID) in lieu of norgestomet at comparable times. Presence or absence of a CL was based on concentrations of serum P 4 on d 14. Pregnancy rates after insemination were greater (P <.01) with luteal treatments than with nonluteal treatments. Embryonal survival between two stages of pregnancy was 87.6%. In Exp. 2, ovarian structures in 50 cows were examined daily using ultrasonography and the same five treatments. Diameter of the ovulatory follicle was greater (P <.05) with the nonluteal treatments (NORG and PRID + no CL) than with the control and luteal treatments (PRID and NORG + CL). Replacement of the dominant follicle during progestin treatment was altered by treatment (luteal status) and stage of the estrous cycle. Fertility was not enhanced by exogenous progestins when a CL was present. In the absence of a CL, progestin (P 4 less than NORG at the doses used) reduced fertility by increasing E 2 and the diameter of the ovulatory follicle and decreasing turnover of dominant follicles.
Article
To examine endocrine and biochemical differences between dominant and subordinate follicles and how the dominant follicle affects the hypothalamic-pituitary-ovarian axis in Holstein cows, the ovary bearing the dominant follicle was unilaterally removed on Day 5 (n = 8), 8 (n = 8), or 12 (n = 8) of synchronized estrous cycles. Follicular development was followed daily by ultrasonography from the day of detected estrus (Day 0) until 5 days after ovariectomy. Aromatase activity and steroid concentrations in first-wave dominant and subordinate follicles were measured. Intact dominant and subordinate follicles were cultured in 4 ml Minimum Essential Medium supplemented with 100 microCi 3H-leucine to evaluate de novo protein synthesis. Five days after unilateral ovariectomy, cows were resynchronized and the experiment was repeated. Follicular growth was characterized by the development of single large dominant follicles, which was associated with suppression of other follicles. Concentrations of estradiol-17 beta (E2) in follicular fluid and aromatase activity of follicular walls were higher in dominant follicles (438.9 +/- 45.5 ng/ml; 875.4 +/- 68.2 pg E2/follicle) compared to subordinate follicles (40.6 +/- 69.4 ng/ml; 99.4 +/- 104.2 pg E2/follicle). Aromatase activity in first-wave dominant follicles was higher at Days 5 (1147.1 +/- 118.1 pg E2/follicle) and 8 (1028.2 +/- 118.1 pg E2/follicle) compared to Day 12 (450.7 +/- 118.1 pg E2/follicle). Concentrations of E2 and androstenedione in first-wave dominant follicles were higher at Day 5 (983.2 +/- 78.2 and 89.5 +/- 15.7 ng/ml) compared to Days 8 (225.1 +/- 78.6 and 5.9 +/- 14.8 ng/ml) and 12 (108.5 +/- 78.6 and 13.0 +/- 14.8 ng/ml). Concentrations of progesterone in subordinate follicles increased linearly between Days 5 and 12 of the estrous cycle. Plasma concentrations of FSH increased from 17.9 +/- 1.4 to 32.5 +/- 1.4 ng/ml between 0 and 32 h following unilateral removal of the ovary with the first-wave dominant follicle. Increases in plasma FSH were associated with increased numbers of class 1 (3-4 mm) follicles in cows that were ovariectomized at Day 5 or 8 of the cycle. Unilateral ovariectomy had no effects on plasma concentrations of LH when a CL was present on the remaining ovary. First-wave dominant follicles incorporated more 3H-leucine into macromolecules and secreted high (90,000-120,000) and low (20,000-23,000) molecular weight proteins that were not as evident for subordinate follicles at Days 8 and 12.(ABSTRACT TRUNCATED AT 400 WORDS)
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A scoring system with 1 to 5 scale was devised to measure body condition of dairy cows at any point during the lactation cycle. Cows were scored on appearance and palpation of back and hind quarters only. Relationships of body weight, frame size measurements, milk production, and characteristics related to the body condition scoring system were determined. During 18 too, 28 cows in each of 29 dairy herds were used for body measurements and body condition scores. Data were obtained from each herd at 3-mo intervals. Body weight and frame size measurements could not be correlated with body condition score. Dairy cows of greatest efficiency of milk production showed no significant increase in body condition during lactation, had fewer days open, but had lower per- sistency of lactation. Dairy cows that in- creased significantly in body condition during lactation were less efficient pro- ducers, had a greater number of days open, and had high body condition scores at the end of lactation. The body condition scoring system is a means of accurately determining body condition of dairy cows, independent of body weight and frame size.
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Using the biotin-streptavidin amplification technique, highly sensitive specific second-antibody enzyme immunoassays for determining LH in bovine plasma with long (48 h) and short (4 h) incubation periods were developed. Biotin was linked to bLH by the N-hydroxysuccinimide method and the product (biotinyl-bLH) used to bridge between streptavidin-peroxidase and the immobilised bLH antibody in competitive tests. The assays were validated and their performance compared with a radioimmunoassay currently in use. The sensitivities of the long and short incubation enzyme immunoassays (8 pg and 15 pg/well, respectively) were superior to that of 5-day incubation radioimmunoassay (100 pg/tube). Plasma interference in both assays were acceptable and volumes of 5 to 40 microliters gave parallel standard curves and comparable LH levels, 10-20 microliters plasma was sufficient to measure LH baseline levels by the long incubation enzyme immunoassay. The mean recovery of added standard bLH to plasma samples containing different endogenous LH was greater than 90% (range 91.7-112) in both assays. The intra- and inter-assay variations of both assays were less than 10 and 17%, respectively. When both enzyme immunoassay and radioimmunoassay were used to measure LH in cyclic cows, the basal levels measured by enzyme immunoassay were lower than that measured by radioimmunoassay. Enzyme immunoassay offers an attractive alternative to the lengthy radioimmunoassay in current usage, with an added advantage of employing non-isotopic label.
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Three experiments with 571 dairy cows indicated that significantly more primiparous cows given two prostaglandin F2 alpha injections 14 d apart conceived within 30 d of first AI than did cows given two injections 11 d apart (84 vs. 62%). Fewer multiparous cows given two injections 14 d apart and inseminated after estrus conceived than did cows given two injections and a progesterone intravaginal coil inserted 8 d after the first injection (42 vs. 66%). Fewer cows given one injection of prostaglandin and inseminated at estrus conceived than did cows given two injections 14 d apart and a progesterone coil (39 vs. 66%). Conception rates of cows given two prostaglandin injections were positively related to plasma progesterone concentrations 2 and 4 d before the second injection (r = .81 and .86). Cows with progesterone concentrations below 5 ng/ml, 2 d before the second prostaglandin injection, and synchronized by two prostaglandin injections or by two injections and a progesterone coil had conception rates of 36 and 63%, respectively. Cows with progesterone concentrations above 5 ng/ml had a conception rate of 75 and 46% in the two treatments, respectively. Conception after estrus synchronization depends on the method and on the plasma concentrations of progesterone. Progesterone coils may be used before AI to enhance fertility in cows with low progesterone concentrations.
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The purpose of these studies was to investigate the pattern and timing of preovulatory endocrine events, estrus and ovulation in Brahman X Hereford (F1) heifers synchronized with norgestomet and estradiol valerate. In Exp. 1, 66 nulliparous and 191 primiparous Brahman X Hereford (F1) heifers were used to estimate the interval from norgestomet implant removal to onset of estrus. The mean interval from implant removal to onset of estrus was 29.8 +/- .5 h, with 80.9% exhibiting estrus within 48 h. Endocrine and reproductive characteristics were examined in detail during Exp. 2 with 37 primiparous heifers. Continuous observation for estrus, 6-h or 2-h blood sampling and ovarian palpation per rectum were employed. All animals were artificially inseminated 48 h after implant removal. Mean interval from implant removal to onset of estrus and to onset of the luteinizing hormone (LH) surge were closely related (r = .91; P less than .0001). Mean intervals from implant removal to ovulation, onset of estrus to ovulation and onset of LH surge to ovulation were 59.1 +/- 2.5 h, 23.3 +/- 1.4 h and 23.1 +/- 1.6 h, respectively. Approximately 73% of heifers exhibited estrus within 54 h after implant removal (optimal timing); conception rate was 59.3% in this subgroup. Conception rate of heifers that did not exhibit estrus within 54 h after implant removal or exhibited an LH surge later than 12 h after estrus (delayed timing) was 10%. Assessment of plasma estradiol-17 beta concentrations suggested that retarded selection and(or) maturation of the preovulatory follicle following implant removal delayed estrus and lowered conception in up to 28% of females timed-inseminated at 48 h.
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The incidence of luteal phase dysfunction as indicated by milk progesterone profiles after artificial insemination (AI) and ovulation was investigated in 21 repeat-breeding dairy cows. Eight (38%) cows had a normal progesterone profile; progesterone levels in skim milk rose to 1·0 ng/ml or higher within five days after insemination (0 dayday of AI) and, thereafter, steadily increased to 2·0 ng/ml or higher at mid-luteal phase. Another 13 (62%) cows had an abnormal pattern of milk progesterone levels which indicated luteal phase defects after AI; seven (54%) of the 13 cows showed a delayed rise of the progesterone level until 6–11 days after AI, two (15%) had a comparatively low level of milk progesterone below 2·0 ng/ml through most of the luteal phase, and four (31%) had a combined pattern of a delayed rise and a low level of milk progesterone during luteal phase. After the AI, five (63%) of the eight cows with a normal progesterone profile conceived, while none of the 13 cows which had insufficient luteal function conceived. It is suggested that delayed formation of the corpus luteum, either combined or not combined with lowered secretion of progesterone during luteal phase is one of the causes of repeat breeding in dairy cows.
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A method for cooling dairy cattle based on repeated wetting to attain maximal water trapping in the coat, followed by its rapid evaporation by using forced ventilation has been examined. Effects examined include duration of wetting, duration of cooling, and density of the animals in the holding area. The coat was wetted by inverted static sprinklers. Also examined was the extent to which the diurnal increase in rectal temperature can be prevented. The maximal decrement of temperature was attained at 30 min after cessation of cooling in all trials. Wetting the coat for 10 s was less effective than for 20 or 30 s; the latter did not differ in their effects. Cooling animals for 15, 30, and 45 min produced decrements in temperature of .6, .7, and 1.0 degrees C, respectively. Maintaining animals at a density of 1.9 m2/cow in the holding area reduced to about half the decrement as compared with a density of 3.5 m2/cow. When cows were cooled 5 times per day for 30 min, temperatures were maintained within 38.2 to 38.9 degrees C during the day, which were significantly lower than for those not cooled.