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Israel Journal of Veterinary Medicine  Vol. 70 (1)  March 2015 Goshen, T. 22
INTRODUCTION
Reproductive efcacy is a key element in dairy farm manage-
ment. A major component in reproductive management is
estrus detection and artifcial insemination (AI) of the cow at
the correct time in the estrus cycle. In Israel, the vast majority
of large dairy farms rely mainly on electronic estrus detection
by pedometry or activity meters (1, 2). Recently, automated
estrus detection aids have become more available and ad-
opted worldwide (3-5). In farms without automated estrus
detection, timed AI (TAI) has become widely accepted as a
reproductive management tool. Te Ovsynch protocol, frst
described by Pursley et al. in 1995 (6), is most widely used
either on its own or in combination with pre-synchronization
(7-10) or post insemination protocols (11, 12).Te Ovsynch
program consists of 2 injections of Gondotropin-releasing
hormone (GnRH), 7 days before, and 48 hours after an injec-
tion of Prostoglandin F2 alpha (PGF
2α). Cows are insemi-
nated 16 to 25 hours after the second injection of GnRH (6).
Te advantages of Ovsynch include the lack of need for estrus
detection by visual or by expensive electronic means, high
insemination rates, reduced losses due to trauma or mastitis
that are estrus related, and fexibility in the number of cows
to be synchronized. Additionally, AI at a fxed times allows
for on farm concentrated work efort for hormone injections,
for AI in a predicted time, and Ovsynch was also described
as a treatment for acyclic cows (13-15). It has been reported
that cows inseminated using the Ovsynch protocol conceived
in comparable rates to the conception rates (CR) of cows
Reproductive Performance in Dairy Cows Synchronized with the
Ovsynch Protocol at Diferent Stages of the Estrus Cycle
Goshen, T.,
1, 2
* Tsitrin, K.
1
and van Straten, M.
1, 2
1
Te Koret School of Veterinary Medicine, the Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel.
2
“HaChaklait” Veterinary Services, P.O. Box 3039 Caesarea Industrial Park 38900, Israel.
*
Corresponding Author: Dr. Tamir Goshen, Te Koret School of Veterinary Medicine, Te Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100,
Israel. Tel: +972 8 9489730. Email: goshen@agri.huji.acl.il
ABSTRACT
Te objectives of the study were to evaluate reproductive performance in cows synchronized with the Ovsynch
protocol at diferent stages of the estrus cycle as detected by pedometry, and to compare the reproductive
performance of cows inseminated by Ovsynch in diferent stages of the estrus cycle (no observed estrus, 0-4,
5-12, 13-17 and 18-24 days after estrus) to cows inseminated by pedometry in Israel. Timing the beginning
of Ovsynch protocol did not afect frst artifcial insemination (AI) conception rate, proportion of cows empty
at 150 days in milk (DIM) or the time from calving to conception. Cows without observed estrus 25 days or
more before initiation of the Ovsynch protocol had rate of cows not pregnant by 150 DIM in comparison to
the control group (Odds Ration (OR) = 1.885, P = 0.013) and longer calving to conception interval than the
control group (155.4 days and 135.7 respectively, P = 0.018). It was concluded that reproductive performance
cannot be improved by combination of pedometry and timed artifcial insemination (TAI); Ovsynch has
low efcacy as a treatment for anestrus. However, other anestrus treatment options should be compared to
Ovsynch.
Keywords: Bovine; Reproduction; Ovsynch; Anestrus; Estrus Detection; Reproduction; Timed
Artifcial Insemination; Pedometry; Ovsynch; Dairy; Anestrus.
Israel Journal of Veterinary Medicine  Vol. 70 (1)  March 2015 23 Ovsynch Protocol at Diferent Stages of the Estrus Cycle
detected in estrus, but with higher pregnancy rates (PR) due
to the higher insemination rates of the Ovsynch treated cows
(1, 6, 10, 16-18).. Te best conception rates of synchronized
insemination are achieved when the Ovsynch protocol is
initiated at days 5-12 of the estrus cycle. Pre-synchronization
protocols evolved to improve conception rates with the aim
of the most commonly used pre-synchronization protocol,
Presynch, to achieve higher proportions of cows that are 5-12
days post estrus at the beginning of the Ovsynch protocol.
Tis is done by injecting PGF
2α twice 14 days apart and ini-
tiation of the Ovsynch protocol 11-14 days after the second
PGF
2α treatment, thus contributing to higher conception
rates at TAI (7, 9).
Te extensive use of estrus detection systems in Israeli
dairy farms makes the sweeping use of TAI protocols redun-
dant. However, cows not detected in heat or repeat breeders
are synchronized in some farms. Te intelligent use of TAI
in cows that are detected in estrus and are not inseminated
due to technical reasons (religious considerations – Saturdays
and holidays, or other reasons) according to the known estrus
date may yield better reproductive performance. Knowledge
of the estrus date (recorded by pedometry) could be used as
a substitute to the Presynch protocol in order to time the
beginning of the Ovsynch protocol to days 5-12 in the estrus
cycle.
Te objectives of this study were to compare conception
rates between cows treated with Ovsynch protocols initiated
at diferent periods of the estrus cycle detected by pedometry
and to compare these to conception rates in cows inseminated
by pedometry alone. Finally, we attempted to evaluate the
efcacy of Ovsynch as a treatment for anestrus.
MATERIALS AND METHODS
Study design and animals
Te study was designed as a retrospective cohort study in
a sample of cows that were inseminated for the frst time
in lactation between January 2006 and December 2007.
Te study was conducted in two commercial Israeli dairy
herds consisting of 450 and 550 Israeli Holstein cows. Cows
were housed in loose housing systems in large, completely
covered open sheds and fed total mixed ration (TMR)
ad libitum. In both herds, cows were milked three times
daily in computer controlled milking parlors. Mean 305
day milk production was approximately 11,500 kg per cow.
All cows were identifed by ear tags, electronic identifca-
tion tags (SAE, Afkim, Israel) and freeze marking. Te
herds were within the practice area of the Ambulatory
Clinic of Te Koret School of Veterinary Medicine, which
provided a complete herd-health service. Both herds were
visited at least three times weekly during the trial period.
Clinical, reproduction, production and management data
were recorded to the farm management software (“NOA”,
Israeli Cattle Breeders Association). Both farms performed
monthly milk recordings through the Central Laboratory
for Milk Recording. Reproductive management was solely
based on AI performed by highly trained technicians em-
ployed by the Artifcial Insemination Service of the Israel
Cattle Breeders Association (ICBA). In both herds, cows
were equipped with computerized pedometry systems
(SAE, Afkim, Israel). Pregnancy diagnosis was performed
by transrectal palpation of the uterus and its content 45-51
days post insemination.
Clinical Examination
All cows were examined routinely between 5 and 12 days
after calving by trained veterinarians, who diagnosed, treated
and recorded periparturient diseases as described previously
(19).
Body condition scoring (BCS scale: 1 = thin, 5 = obese)
was recorded before dry-of, at the routine post-partum
examination (5-12 days after calving) and between 40 to 60
days after calving (peak yield BCS).
Ovsynch and treatment groups
Te Ovsynch group (OS) included cows treated with the
Ovsynch protocol. Hormonal synchronization was used on
the farms as part of a study evaluating the efcacy of Ovsynch
in comparison to pedometry, or for re-synchronization of
animals detected in heat during Saturdays or holydays (the
farms did not inseminate cows during Saturdays for religious
reasons). OS Cows were treated with IM injection of 150
µg Gonadorelin Acetate (Gonabreed, Parnell Laboratories,
New Zealand) followed seven days later by IM injection of
500 µg Cloprostenol Sodium (Estrumate, Schering-Plough,
Germany), followed two days later with another IM injection
of 150 µg Gonadorelin Acetate. OS cows were insemination
16-24 hours after the last GnRH injection regardless of heat
signs.
Research Articles
Israel Journal of Veterinary Medicine  Vol. 70 (1)  March 2015 Goshen, T. 24
Cows from the OS group were individually matched
to the control cows by farm, calving year and parity. When
possible, the calving season, calving diseases and calving to
frst AI interval (voluntary waiting period) of the matched
control cow were also similar.
In the second part of the study the cows were divided
into six groups:
1. Control (CO) – cows inseminated at the detected
heat.
2. Anestrus (AN) – cows inseminated after treatment
with Ovsynch protocol with no detected estrus in the previ-
ous 24 days.
3. Ovsynch at days 0-4 (OS4) – cows inseminated after
treatment with Ovsynch protocol 0-4 days after detected
estrus.
4. Ovsynch at days 5-12 (OS12) – cows inseminated
after treatment with Ovsynch protocol 5-12 days after de-
tected estrus.
5. Ovsynch at days 13-17 (OS17) – cows inseminated
after treatment with Ovsynch protocol 13-17 days after
detected estrus.
6. Ovsynch at days 18-24 (OS24) – cows inseminated
after treatment with Ovsynch protocol 18-24 days after
detected estrus.
Statistical analysis
Computerized data were retrieved from the farm comput-
ers and ICBA central computer and analyzed using Excel
(version 2010, Microsoft, Redmond, WA) and SPSS 17.0.1
(SPSS Inc., Chicago IL, USA). Lactation Incidence Risk
(LIR) for all recorded diseases and reproductive performance
parameters were evaluated for Control and Ovsynch cows.
Te same evaluation was done for cows in the diferent
Ovsynch timing groups.
Reproductive performance parameters included frst arti-
fcial insemination conception rate (1
st
AI CR), the interval
from calving to pregnancy (Days Open), time from 1
st
AI
to conception (Waste days) and the proportion of cows not
pregnant > 150 days after calving (Empty at 150 DIM ie.
Days in Milk = Days from Calving).
Te efect of Ovsynch on dichotomous outcome variables
was evaluated using conditional multivariable logistic regres-
sion modeling.
Separate analysis was done for Ovsynch versus Control
cow and for Ovsynch timing groups as an independent vari-
able. Various parameters and disease conditions were tested
in the models as possible confounders. Tese included: farm,
calving season (May to September = Summer; October to
April = Winter), twin calving, retained placenta (RP, retained
fetal membranes ≥ 24 hrs. post calving), clinical metritis
(CM), ketosis, displaced abomasum, body condition loss
≥0.5 between calving and peak milk yield, mastitis at calving,
mammary edema at calving, stillborn calves and induction of
calving. Crude bivariate associations of outcome and potential
confounding variables with treatment were initially assesses
by use of Pearson χ
2
asymptotic 2-sided tests of signifcance
for reproductive dichotomous parameters and student’s T test
for waiting period and days empty. To build the models, the
Control versus Ovsynch timing group variables were forced
into the model and subsequent covariates with signifcance
of P ≤ 0.25 were included in primary multivariate models. Te
fnal models were built with entry criteria set at P < 0.05 and
exit criteria set at P > 0.10. For all analysis, values of P < 0.05
were considered signifcant. Te Odds Ratios (OR) were
calculated for all variables in the model.
Te conditional logistic multivariate analysis was done
using the Cox regression procedure for dichotomous out-
come variables with pairing as strata, and linear regression
procedure was used for scale outcome variables. Te efects of
Ovsynch treatment and its timing in the estrus cycle on days
open were evaluated using Kaplan-Meier survival analysis.
As the segmentation of the waste days is not equal, there is
an association between specifc period of times and elevated
risk for conception. Also the risk of conception is higher on
the frst AI and declining later. To compensate for these facts,
the efect of the treatment was analyzed using a Proportional
Odds model as proposed by Cox.
For all survival analyses, days open were limited to 200
days, cows not pregnant at 200 DIM were considered as empty.
RESULTS
Descriptive statistics
During the study period 267 cows were treated by Ovsynch
in the study farms. Control cows were matched and difered
from the Ovsynch cows only in waiting days (Table 1).
Reproductive performance
Te Ovsynch protocol and the timing of its beginning in the
estrus cycle did not afect signifcantly the 1
st
AI CR (Table 2).
Research Articles
Israel Journal of Veterinary Medicine  Vol. 70 (1)  March 2015 25 Ovsynch Protocol at Diferent Stages of the Estrus Cycle
Te control cows Empty at 150 DIM rate was lower
than in the Ovsynch cows (36.7% and 44.9 respectively;
OR = 0.817, P = 0.0321, table 2). Te timing of the Ovsynch
protocol in the estrus cycle afected the probability of groups
1 and 5 to be Empty at 150 DIM.
Only group 1 (Anestrus group) difered from the other
Ovsynch groups. For further analysis of cows Empty at 150
DIM, the cyclic Ovsynch groups (3-6) were united. Te cyclic
status of the cows at the initiation of the Ovsynch protocol
afected signifcantly the Empty at 150 DIM rates. Cows in-
seminated by Ovsynch protocol without a detected estrous 24
days before the initiation of the protocol had higher Empty
at 150 DIM rate in comparison to the control group (OR
to be empty at 150 DIM = 1.885, P = 0.013, table 3). Cyclic
cows inseminated by Ovsynch protocol did not difer from
cows inseminated in pedometry detected estrus (Table 3).
Cows inseminated by Ovsynch had longer open peri-
ods than control cows (mean days open = 146.1 and 135.7
respectively, P = 0.017). Tis diference was mainly due to
the cyclic status of the cows. Cyclic cows inseminated by
the Ovsynch protocol did not difer from the control (mean
days empty = 141.2, Figure 1), while the anestrus cows had
signifcantly longer empty period (mean days empty = 155.4,
Figure 1).
Table 1: Descriptive statistic of the calving diseases LIR and waiting
period of the Ovsynch and Control cows.
Parameter Ovsynch Control Overall P value
Farm:
A 197 197
394
(73.8%)
1
B 70 70
140
(26.2%)
1
Parity :
1 95 95
130
(35.6%)
1
2 61 61
122
(22.8%)
1
3+ 111 111
222
(41.6%)
1
Summer Calving’s 37.1% 35.2% 36.1% 0.652
RP
1
13.9% 17.2% 15.5% 0.282
CM
2
37.1% 36.3% 36.7% 0.857
Ketosis 19.1% 16.5% 17.8% 0.428
Waiting period
3
100.7 95.9 98.3 0.007
1 – Retained placenta, retained fetal membranes ≥ 24 hrs.
2 – CM – Clinical/Puerperal metritis.
3 – Waiting period – calving to 1
st
service interval.
Table 2: Descriptive statistics of diferent reproductive parameters
in the control (Inseminated at estrus) and the diferent study groups.
Ovsynch Group*
Over
all**
Control 2 3 4 5 6
N 267 93 32 98 25 19 267
1
st
AI CR
1
39.7% 35.5% 46.9% 34.7% 40% 31.6% 36.7%
Empty >150
DIM
2
36.7% 54.8% 46.9% 36.7% 48% 31.6% 44.9%
Days empty
3
144.9 169.4 163.1 147.5 161.5 145 158.1
Waste days
4
27.1 28.9 33.6 23.5 30.5 24.1 27.3
* group 2 – Ovsynch protocol started ≥25 days from estrus or no estrus
before Ovsynch, group 3 – Ovsynch protocol started 0-4 days after
estrus, group 4 – Ovsynch protocol started 5-12 days after estrus,
group 5 – Ovsynch protocol started 13-17 days after estrus and group
6 – Ovsynch protocol started – 18-24 days after estrus.
** Over all – all Ovsynch cows.
1
1
st
AI CR – the proportion of cows conceived from 1
st
artifcial
insemination.
2
Empty >150 DIM – the proportion of cows not pregnant > 150 d after
calving.
3
Days empty – Mean calving to conception interval. Maximum value is
250 days.
4
Waste days – Mean 1
st
AI to conception interval.
Table 3: Logistic regression model summaries of the relationship
between the cyclic status of the cows when Ovsynch is initiated
and the Empty at 150 DIM in cows inseminated by pedometry or
by Ovsynch.
Variable β S.E. df Sig. O.R.
95% CI for O.R
Lower Higher
Group:
Control
2 0.047 Reference
Anestrus
Ovsynch
1
0.634 0.256 1 0.013 1.885 1.141 3.113
Cyclic
Ovsynch
2
0.170 0.209 1 0.416 1.185 .787 1.786
Parity :1 2 <0.001 Reference
2 -0.045 0.278 1 0.871 1.885 1.141 3.113
3+ 0.861 0.232 1 <0.001 1.185 0.787 1.786
Calving
Diseases
3
0.353 0.202 1 0.081 1.423 0.957 2.117
Long Waiting
period
4
1.073 0.222 1 <0.001 2.923 1.890 4.520
Constant -1.403 0.266 1 <0.001 0.246
1 – Cows inseminated after treatment with Ovsynch protocol with no
detected estrus in the previous 24 days.
2 – Groups 3-6 combined. Te cows had a detected estrus 24 days or less
prior to the beginning of the Ovsynch protocol.
3 – Retained placenta, clinical metritis and ketosis.
4 – Calving to 1
st
AI interval ≥108 days (higher quartile).
Research Articles
Israel Journal of Veterinary Medicine  Vol. 70 (1)  March 2015 Goshen, T. 26
Higher lactation numbers and lower body condition
scores at peak yield were associated with reduced pregnancy
rates. Post-partum endometritis was associated with reduced
pregnancy rates, but the efect declined as DIM increased.
Summer calving tended to reduce the pregnancy risk
(OR = 1.079, P = 0.0607). Te OR to become pregnant of
cows inseminated by Ovsynch at 0-4 or 13-17 days after
estrus was reduced (OR = 0.706, P < 0.0001 and OR = 0.881,
P < 0.0001 respectively).
DISCUSSION
Te novelty of this study is in combining the TAI with
automated estrus detection systems, and by comparing the
conception rate of cows inseminated by Ovsynch protocol
started at diferent times of the estrus cycle. Te main fnding
in this study was that the timing of the beginning of the
Ovsynch protocol in the estrus cycle had no efect on 1
st
AI
conception rate. Tis fnding was unexpected as Presynch
protocols are widely used for CR improvement (7, 8, 20,
21). Te purpose of the Presynch protocols is to lower the
proportion of anovular cows (22), and to time the beginning
of the Ovsynch protocol to the period of time where maximal
reproductive efcacy can be achieved at days 5-12 of the
estrus cycle (20, 21). Te start of the Ovsynch protocol at
this timing is supposed to ensure the ovulation of smaller
follicles at the timed AI, with higher CR (20). Modifcation
of the Ovsynch protocol by adding presynchronization had
improved pregnancy rates in previous studies (7, 9, 10, 23).
However, the results of this study did not demonstrate advan-
tage (as refected in the measured reproductive parameter) to
the starting of synchronization protocol at days 5-12 of the
estrus cycle or to any other diferent timing. Te benefcial
efects of presynchronization with prostaglandin might be
due to efects on pyometra and subclinical endometritis (24),
hence not present in this study.
Te anestrus cows that were treated by Ovsynch did not
difer signifcantly from the other study groups in 1
st
AI CR.
Te Anestrus cow group was actually composed of two dif-
ferent populations of cows: cyclic cows which the pedometry
system failed to detect in estrus and acyclic cows. In some
of previous studies, cows with anovular follicles had low CR
when inseminated by Ovsynch (13, 25). As the anestrus cows
group included the cyclic cows not detected by pedometry
system, this sub-population may confound the efect of the
acyclic cow population on 1
st
AI conception.
Tis confounding efect was limited to the 1
st
AI, as
anestrus cows treated by Ovsynch, had longer calving to
conception interval (Figure 1), a fact that can be explained
by the continues efect of the acyclic cows sub-population on
pregnancy rate of the anestrus cows. Te longer calving to
conception interval demonstrates a low efcacy of Ovsynch
as a treatment for ovarian inactivity as was documented be-
fore (13, 26). However, as the control group was composed
of cyclic cows detected in estrus by pedometry, the efcacy
of Ovsynch as a treatment for ovarian inactivity should be
compared to other treatment options.
Over all, cows inseminated based on Ovsynch or by
pedometry did not difer in the 1
st
AI conception rate. Tis
fnding is similar to fndings in previous studies in Israel (1)
and worldwide (5, 6, 10, 17), suggesting that Ovsynch can
replace pedometry in farms without pedometers or activity
meters, or in farms where management conditions limits
the efcacy of estrus detection by electronic aids. Recently,
Neves et al. (5) found that in north American conditions
automated estrus detection systems are at least equal to TAI
in the reproduction efcacy, despite the fact that this study
was conducted in free stall commercial dairy herds (as op-
posed to the loose shade Israeli system). Tey also found
Figure 1: Survival plot of pregnancy rate in Control cows inseminated
at estrus detected by pedometry (
—
), Cyclic cows inseminated by
Ovsynch protocol (
....
) and Anestrus cows inseminated by Ovsynch (—).
Te mean survival time of the Anestrus cows difered signifcantly from
the Control cows in the Log Rank test (P = 0.018, mean survival time
of 155.4 and 135.7 respectively). Te Cyclic cows did not difer from
the Control group (mean survival time of 141.2 and 135.7 respectively).
Days In Milk
Research Articles
Israel Journal of Veterinary Medicine  Vol. 70 (1)  March 2015 27 Ovsynch Protocol at Diferent Stages of the Estrus Cycle
that herd level management may confound the efects of the
reproductive management system.
CONCLUSIONS
Timing Ovsynch with estrus detection did not improve the
reproductive performance of treated cows. In farms with con-
ditions allowing for high efcacy of estrus detection systems,
and where such systems are available, Ovsynch protocols may
be redundant as a reproduction management tool for all cows.
Te reproductive performance of anestrus cows treated
by Ovsynch is not comparable to the cyclic cows; however
the efcacy of Ovsynch as a treatment of anestrus should be
compared to other treatment options.
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Research Articles