Influence of dexamethasone administered to normal cycling mares either one day before
or on the day of mating, upon endometrial oedema, uterine fluid and pregnancy rates.
Abstract
This present study describes the effect of a single dose of (10 mg) dexamethasone administered subcutaneously
to TB mares either on the day before or the day of mating. A non treated control group was included. Every
mare which had to be mated was included in this study, belonging to either the treated or the non treated control
group. We distinguished between foaling, maiden and barren mares. Endometrial oedema and uterine luminal
fluid scores before and after the dexamethasone were recorded and the pregnancy rates were examined. The
author concluded that a single dose of dexamethasone, on a practical basis administered 24 hours before mating,
reduced oedema directly.. Pregnancy rates might be improved. Older mares are more difficult to get in foal.
When treated a day before mating, a significant improvement on pregnancy rate was found in mares older than
16 yrs. Oedema pre-mating, fluid pre-mating and status had no significant effect on pregnancy rate.
1. Introduction
In early oestrus it is common to visualise with ultrasound, free endometrial fluid accumulations often at the base
of the uterine horns. These may be due either to lymphatic stasis/ delayed uterine clearance and/or incomplete
cervical relaxation. Normally this disappears before the time of mating/AI. This fluid is a non-inflammatory
transudate produced by the endometrial glands rather than an inflammatory exudate. However a transudate may
quickly develop into an exudate if bacterial contamination occurs. It may therefore be preferable if this fluid has
been removed before mating [1]. In normal mares these small fluid accumulations in early oestrus appear to be
correlated with a degree of endometrial oedema. [1].
After mating, there is a naturally occurring inflammatory response to semen in combination with a humoral or
antibody- mediated defence mechanism. This is thought to be a physiological process to remove excess
spermatozoa, seminal plasma and contaminants, before the entry of the embryo into the uterus. Cytological
examination of the fluid shows it to be neutrophilic with evidence of phagocytosis of sperm and bacteria. There
is release of PGF2a which increases uterine contractility enhancing clearance of the uterine exudate. Mares
susceptible to persistent mating induced endometritis, PMIE) have a reduced response (either phagocytosis or
fluid clearance is impaired), most important is dysfunction of the uterus contractility [2]. Mares susceptible to
PMIE may have increased uterine oedema score with slower dissipation of the oedema as ovulation approaches.
They may even have an increased score due to an over-reaction to spermatozoa challenge. It has been suggested
that mares with prominent uterine oedema after ovulation should be suspected of being susceptible of
endometritis after mating. [3]
Reduced conception rate mares with PMIE may be due to the continued presence of neutrophils in the uterine
lumen which are cytotoxic for gametes and embryo’s [4].
Why dexamethasone?
Modulation of the inflammatory response at breeding time was tried to achieve using the glucocorticosteroid
dexamethasone. This should decrease oedema in the uterus, therefore reducing the post-breeding endometrial
fluid, which improves restore of the mucociliary flow and mucus composition and therefore improves uterine
clearance [7]. Dexamethasone has its antiflogistic effect by blockage of fosfolipase enzymes & change in
transcription of different kinds of (anti)-inflammatory proteins, decreasing the formation of TNF, interleukine1, PGF, tromboxanes and leukotrients and inhibiting the uptake of antigens by fagocytotic cells and the protein
formation in activated T and B- cells
It has its immunosuppressive proporties by inhibiting the migration of cells and fagocytosis .
The pharmaceutical drug Voren [24] is used as dexamethasone treatment. Voren contains an isonicotinate-form
which has higher glucocorticosteroids potency then dexamethasone on its own. Because of this we achieve a
higher blood-level and a longer working action (3-4 days) with a single injection.
Voren contains 1 mg of dexamathasone-21-isonicotinate per ml. It is a potent long acting corticosteroid with a
therapeutic effect lasting for approximately 4 days. Voren is easily stored at room-temperature, out of the light. It
is relatively cheap and easy to inject i.m. or s.c.
1
Previous investigation showed different results using the dexamethasone therapy. Bucca at al.(2008) [7] noted
reduced oedema when dexamethasone was administered at the time of mating in PMIE predisposed mares, but
did not find a significant increase in pregnancy results. On the other hand Samper J.C. 2011 [11] found
pregnancy rates to be increased when oedema at mating is reduced.
The present study evaluates the effects of the administration of a single dose dexamethasone (Voren10 ml s.c.)
and the optimal time around mating without distinguishing between mares to improve overall pregnancy rates.
2. Materials and methods
Animals
In this field trial during the months of February, March and April), we utilised 261 thoroughbred mares on a
commercial farm with a total of 317 cycles. Mares were divided in three groups: foaling, maiden and barren
mares, and then randomly assigned to different treatment groups:
1. Dexamethasone treatment 24h before mating
2. Dexamethasone treatment on the same day of mating
3. Control group
All the mares used in this study were mated naturally. The aim was to mate the mare once in the period of time
between 24 hrs before ovulation to 12 hrs after ovulation. For this reason mares were routinely examined by
palpation and ultrasound examination per rectum every other day (Monday-Wednesday- Friday), except for the
weekend. When a mare was examined for the first time, both vaginal and a rectal examination were made.
Mares apparently in seasonal anoestrus, were re-examined 7days later. Those in the transitional phase, with a
follicle larger than 20 mm were treated with an intravaginal progesterone releasing device (PRID, CIDR, CuMate). The mare was re-examined after 7 days and the device removed providing a follicle of at least 30mm had
developed, or was left in for another 2-3 days.
If at the first examination a CL was detected, according to its estimated age the mare was treated with between
0.3 – 1.0ml, (22-75mcg ) subcutaneously of the PGF 2α analogue d-Cloprostenol (Genestran or Dalmazin) to
induce luteolysis and shorten the interval to the next oestrus.
When the mare was found in oestrus with a mature follicle, she was mated either the same day, one or two days
later (depending on when ovulation was predicted). All mares were given a routine treatment of intrauterine
antibiotic (6cc of injectable procaine penicillin and 6cc framycetin sulphate) either one or two days after mating
followed one day later by 25 units oxytocin i.v. If necessary, to avoid a second mating, ovulation was induced
by an injection of hCG (1500 IU Chorulon) s/c. Mares were always re-examined to determine ovulation and the
possibility of multiple ovulation. Two mares were given Ovuplant rather than hCG.
All mares had their tail bandaged and the perineum washed with clean water before mating.
Mares which failed to ovulate were excluded of the project.
After ovulation, the mare was examined for pregnancy on either day 13 or 14 (12 days after detection of
ovulation).
Pregnancy diagnosis was made with a real-time, B-mode ultrasonography, using a 5 MHz linear array
transducer. When an embryonic vesicle was detected the mare was examined again 7 days later (day 20/21) to
detect an embryo proper (pulsating heart). Mares with twinembryos or known to have multiple ovulation were
re-examined at shorter intervals. On day 29-30 pregnant mares were re-examined to determine the normal
development of the embryo moving centrally due to formation of the allantois. The final pregnancy examination
was made about day 42, where the conceptus was about 55-70 mm diameter and the foetus located centrally,
hanging by the umbilical cord. After this check the mares were sent home.
Mares found with vesicle at 13-14 days, were noted as pregnant although the vesicle may have been found to
have resorbed by the next examination. The shape, size and position of all endometrial and lymphatic cysts,
which could be confused with embryonic vesicles, were recorded before the first examination for pregnancy.
If the mare was found to be not pregnant, or lost her vesicle for whatever reason (defected oocytes, failure
[25])the mare was mated again at the next oestrus. This mating was classified in a different group than the first
(if first mating was a ‘treated same day’ than the second was left untreated as a ‘control’ and vice versa).
Treatment
Either one day before or on the same day of mating (within 4 hours from the moment of mating), mares were
administered 10 cc of dexamethasone isonicatinate (Voren) by subcutaneous injection. Mares were chosen
randomly for treatment (there was no difference made between mares based on the oedema score or what so
ever). The dose of 10 cc is based on the mean weight of a middle-age Thoroughbred horse (500 kg 1 ml/ 50 kg
bw).
2
Diagnostic variables considered:
The independents variables are:
- Age (1=0-5 yrs; 2=6-10 yrs; 3=11-15 yrs; 4=16-20 yrs; 5= >20 yrs); [8nieuw]
- Status (1= maiden mare; 2= barren mare; 3= mare with foal);
- Treatment (1= the 24 hrs before mating; 2= the SD (same day); 3= control);
- Depth of fluid before mating (1 = 0-5 mm; 2= 6-20 mm; 3=21-30mm based on the amount of mares
available), the last measurement before mating was used;
- Intensity of oedema before mating (1=0-0.5; 2=1.0-2.0; 3=2.0-3.5 based on the amount of mares
available), the last measurement before covering was used.
The dependent variables were:
- pregnancy rate (0= pregnant; 1= not pregnant)
- Depth of fluid on day 1, 2 or 3 after mating (1 = 0-5 mm; 2= 6-20 mm; 3=21-30mm based on the
amount of mares available);
- Intensity of oedema on day 1,2 or 3 after mating (1 = 0-0,5; 2= 0,51-2; 3=2,1,3,5 based on the amount
of mares available);
Endometrial oedema score [21]
Uterine oedema was assessed subjectively as per transrectal ultrasonography of the horns and uterine body. The
oedema score was scaled from 0 – 4 in 0.5 increments:
0
a homogenous endometrium coincident with that of a ‘dioestrus-like echotexture.
0.5
slight oedema
1
definite but mild oedema
1.5
mild to moderate
2
moderate oedema, often the maximum level seen during normal oestrus
2.5
moderate to heavy
3.0
heavy oedema, occasionally seen during normal cyclicity
3.5
gross, possibly pathological oedema
Oedema scores are averages of findings of the whole uterus.
Endometrial fluid score:
Fluid scores were made from measurements of the depth of the largest pocket of fluid. If only small amounts of
fluid were present, they tended to distribute in several pockets.[1].
Statistical analysis
Data are presented in pregnancy results (% and total). All variables are made categorical and were compared
using Chi2 – test and Odds-ratio (logistic regression).
3
3. Results
a. Overall- Pregnancy results
Maiden mares and mares with foal had a non significantly higher pregnancy rate than barren mares. A slightly
higher percentage of pregnancies was found in the mares treated on the day before mating (24 hrs) group when
compared with the control group and the mares treated the same day of mating.
Table 2. Overall Pregnancy results
Total % preg
Status
Maiden
Barren
Mare with foal
Treatment
24 hrs before
The SD
Control
Fluid pre covering
0-5 mm fluid pre
> 5 m fluid pre
Oedema precovering
0-0.5 oedema pre
0.5 -2 oedema pre
> 2 oedema pre
Age
0-5 yrs
6-10 yrs
11-15 yrs
16-20 yrs
> 20 yrs
52
115
150
73.1 %
60.0 %
69.3 %
91
83
143
69.2 %
66.3 %
65.0 %
287
28
67.5 %
64.3 %
120
186
8
65.0 %
67.2 %
75.0 %
37
113
91
32
11
78.4 %
69.9 %
64.8 %
53.1 %
27.3 %
Chi2
0.155
Sig.
0.436
0.801
0.406
0.189
0.225
0.863
0.771
0.011
0.023
The only independent variable with statistically significant (.011) influence on pregnancy is age. A decrease in pregnancy results is seen in
the table.
According to the Chi2- test there were no significant influences from any of the factors investigated, except for
the ‘age’. An ascending line in the odds ratio of ‘not getting pregnant’ and the age of the mare was found in the
final model of logistic regression. Especially in the groups from 16-20 yrs (53.1% pregnant, p=.024) and older
than 20 yrs (27.3% pregnant, p=.003) there was a significant influence on the pregnancy rate (0.024 and .003
respectively).
Only age (p= 0.023) stayed in the final model of logistic regression for pregnancy results, treatment (p=0.406)
was forced to stay in. Oedema pre-mating (p=0.771), fluid pre-covering (p = 0.225) and status ( p=0.436) were
not significant (table 2). No significance correlation between age and treatment can be seen (table 3). But the
difference in Odd-ratio indicates a higher odd of getting pregnant in the treated 24 hrs group.
Table 3. Multivariate logistic regression result on only treatment x age
Sig.
Odds ratio
Age: 6-10 yrs
.244
1.700
Age: 11-15 yrs
.114
2.063
Age: 16-20 yrs
.024
3.348
Age: > 20 yrs
.003
10.274
Treatment: 24 hrs
.268
.704
Treatment: Same Day
.837
.938
The code of reference for age is 0-5 yrs, the code of reference for treatment is the control group. Support of table 3 is seen her. Higher
pregnancy rates in younger mares are visible. Treatment doesn’t have an effect on pregnancy rate (as showed in table 3).
b. Pregnancy results in the individual groups: maiden mares, barren mares, mares with foals.
In both the barren as the maiden mare groups a higher although not significant pregnancy rate was seen in both
the treated (24hrs as SD) groups if compared with the control group.
In the barren mares group the odds ratio of not getting pregnant in the treated Same Day group is very close to
the control group. The treated 24 hrs group showed a lower although not significant odds ratio of not getting
pregnant (0.488) and therefore twice a higher odd of getting pregnant (1/ 0.488 =2.049).
4
In the maiden mares group the treated 24 hrs group showed a lower although not significant odds ratio of not
getting pregnant (.290) and therefore 3½ higher odds of getting pregnant (1/ 0.290 =3.45). This is (1/.516 = 1.94)
almost twice in the treated SD group.
In the foaling mares groups both the treated groups have higher although not significant odds of not getting
pregnant than the control group. The treated 24 hrs ago group has almost the same odd as the control group.
Table 4. Pregnancy results in the individual status groups.
% Preg
Total Chi2
Sig.
Barren mares
Treatment:
0.691
0.396
Control
65.4%
26
Treated 24 hrs
63.0%
27
0.175
Treated same day 56.5%
62
0.757
Age:
0.072
0.119
0-5 yr
100%
2
6-10 yr
76.7%
30
0.999
11-15 yr
52.3%
44
0.999
16-20 yr
47.4%
19
0.999
21-25 yr
37.5%
8
0.999
Maiden mares
Treatment:
Control
Treated 24 hrs
Treated same day
Age:
0-5 yr
6-10 yr
11-15 yr
Foaling mares
Treatment:
Control
Treated 24 hrs
Treated same day
Age:
0-5 yr
6-10 yr
11-15 yr
16-20 yr
21-25 yr
73.7%
75.0%
71.4%
19
12
21
76.9%
57.1%
0%
26
14
1
69.6%
65.9%
71.7%
46
44
60
77.8%
69.6%
76.1%
61.5%
0%
9
69
46
13
3
Odds ratio
0.488
0.851
5.516*10^8
1.678*10^9
2.073*10^9
3.127*10^9
0.975
0.478
0.290
0.516
0.342
0.240
0.456
0.267
0.104
0
4.198
0
0.820
0.778
1.062
1.386
0.074
0.898
0.498
0.845
0.614
0.913
0.425
0
1.537
1.101
2.197
0
The code of reference for age is 0-5 yrs. The code of reference for treatment is the control group. No statistical significant changes are
showed. The treated 24 hrs ago mares show higher odds ratios of getting pregnant in the barren and maiden mares (1/.488 = 2.049 and
1/.290 = 3.448 resp. In the foaling mares no difference in treatment is seen at all. Age seems to make difference on pregnancy results in all 3
group (barren, maiden, foaling), again: younger mares have better pregnancy results.
c. Pregnancy rates in treated mares older 16 yr.
In contrast to the mares younger than 16 yrs old (p=0.956) a significant higher pregnancy rate (p=0.032; Odds
ratio of 0.140 times ‘not pregnant’ in comparison with the control group) was achieved in the group op mares
older than 16 years who got treated the day before covering. No significant difference was found in the mares
older than 16 years treated the same day of mating.
Tabel 5 Pregnancy in older mares
% Preg
Total
Mares > 16 yr
Control
38.1 %
21
Treated 24 hrs
72.7%
11
Treated same day 36.4%
11
Sig.
Odds ratio
0.077
0.032
0.997
0.140
1.003
The code of reference for treatment is the control group. Mares older than 16 and treated 24 hrs before covering have statistically higher
odds ratio of getting pregnant (1/.140 = 7.143 times) than the other treatment groups.
d.Oedema post mating
The oedema scores measured on day 1, 2 and day 3 were used in the statistics. Table 7 shows on how many
measurements the graphs are based. No significance influence from one of the independent variables on the
oedema post mating on day 1,2 or 3 was found.
5
Table 6. Relative frequency table for oedema post covering measurements.
24 hrs
Same day
Control Maiden Barren
With foal
Total
Day 1
0-0,5 mm
>0,5 -2 mm
>2 mm
Day 2
132
75
54
3
110
0-0,5 mm
>0,5 -2 mm
>2 mm
Day 3
49.3%
40.7%
0
4.0%
1.9%
0
46.7%
57.4%
100.0%
20.0%
13.0%
0
32.0%
48.1 %
66.7%
48.0%
38.9%
33.3%
20.9%
29.2%
22.7%
45.3%
29.2%
41.8%
33.7%
41.7%
35.5%
15.1%
20.8%
0
30.2%
50%
0
54.7%
29.2%
0
86
24
0
101
0-0,5 mm
21.2%
31.3%
47.5%
13.1%
39.4%
47.5%
99
>0,5 -2 mm
0
50.0%
50.0%
0
50.0%
50.0%
2
>2 mm
0
0
0
0
0
0
0
Mares in the control group have the highest edema score, which reduces the slowest in the 3 days.
Maiden mares have the lowest percentages of edema after covering.
Figure 1. Average edema development from 3 days before till 3 days after covering
Treated 24 hrs ago
Edema score before/ after covering
Treated Same Day
Control
Avarage Edema score
1,4
1,2
1
0,8
0,6
0,4
0,2
0
-3
-2
-1
0
1
2
3
Days (-3, mating, +3)
Oedema seems to decrease directly after administering the dexamethasone, but theo edema score after 3 days appears to be the same in all
three treatment groups. On day 0 (mating day) only 3 measurements were available in the treated 24 hrs group (table 8).
Table 7. Numbers of mares used in the calculation of average in figure 1.
OEDEMA
Same day
Day:
24 hrs
Control
Average:
Total
Average
Total
Average
Total
-3
0,75
8
0,766
32
0,648
28
-2
0,931
58
1
3
1,095
63
-1
1
3
1,094
85
1,246
57
0
1,025
80
0,167
3
0,923
52
1
0,8
5
0,588
57
0,761
69
2
0,337
43
0,463
27
0,321
39
3
0,121
33
0,067
20
0,136
44
Very low number of measurements is available at day -2 and mating in the 24 hrs group and at day -1 and day1 in the treated same day
group.
In all groups a decrease in the oedema after mating was seen. Although not significant a decrease in the oedema
was seen directly after treatment, both in the mares treated 24 hrs before mating and in the mares treated the
same day of mating.
e. Fluid postrmating
The fluid scores measured on day 1, 2 and day 3 were used in the statistics. The table shows on how many
measurements the graphs are based. No significance influence from one of the independent variables on the
fluid post covering on day 1, 2 or 3 was found.
6
Table 8. Relative frequency table for fluid post covering measurements.
24 hrs
Same day
Control Maiden Barren
Day 1
With foal
Total
130
0-5 mm
47.1%
7.1%
45,7%
15.7%
37.1%
47.1%
70
>5 -20 mm
41.7%
2.1%
56.2%
22.9%
37.5%
39.6%
48
>20
33.3 %
0
66.7 %
8.3%
58.3%
33.3%
12
Day 2
112
0-5 mm
22.8%
47.4%
29.8%
10.5%
33.3%
56.1%
57
>5 -20 mm
25.0%
32.7%
42.3%
21.2%
38.5%
40.4%
52
>20
33.3%
33.3%
33.3%
33.3%
0
66.7%
3
Day 3
103
0-5
21.7%
28.9%
49,4%
10.8%
42.2%
47.0%
83
>5 -20
15.0 %
40.0%
45%
20.0%
30.0%
50.0%
20
>20
0
0
0
0
0
0
0
Mares in the control group have the highest fluid score, which reduces the slowest in the 3 days.
Treated Same Day
Avarage Fluis scores
Fluid score before/ after covering
Treated 24 hrs ago
Control
16
14
12
10
8
6
4
2
0
-2
-3
-2
-1
0
1
2
3
Days (-3, mating, +3)
Figure 2. Average fluid development from 3 days before till 3 days after covering. No influence on the fluid is seen directly after the
administration of the dexamethasone.
Table 9. Numbers of mares used in the calculation of average in figure 2.
FLUID
Same day
Day:
24 hrs
Control
Avarage
Total
Avarage
Total
Avarage
Total
-3
0
6
0.667
30
1,84
26
-2
0,991
56
0
3
0,254
61
-1
0
3
0,703
86
0,757
63
0
3,389
79
15
12
4,678
49
1
3,5
6
8,169
56
8,901
70
2
6,216
43
7,782
28
7,742
38
3
4,071
32
1,938
21
3,01
46
Very low number of measurements is available at day -2 in the 24 hrs group and at day -1 and day1 in the treated same day group.
Fluid increases in all three groups the same day or just after mating. In the groups of mares treated 24 hrs before
mating it reaches the highest peak at the moment of mating, while in the mares treated on the same day of mating
it peaks 2 days after mating and in the control group it peaks 1 day after mating. Similarly to the oedema also the
intraluminal fluid decreases in all three groups 2 and 3 days after mating.
f. Correlation between oedema post-covering and fluid post-covering
The relationship between amount of fluid post- covering (day 1,2,3,) and amount of oedema post-covering (day
1,2,3) was investigated using a Spearmann product-moment correlation coefficient. Only the fluid after mating
on day 2 showed a significance correlation (rho=0.175) with the oedema after mating on day 2 (p= 0.036). But
with a coefficient of determination of 4% (r2=0.1752 =0.04) only 4% of the oedema post covering on day 2 can
be explained by the fluid postmating on day 2, which means that 96% can not.
Between the other variables no significance correlation was shown. The Rho- results were all between -0.10 and
+ 0.125.
7
Discussion
This study investigated the influence of 10 cc (10 mg) Dexamethasone on endometrial oedema and intra-luminal
fluid patterns around the time of mating , and on pregnancy rates.
All the mares used in this study were mated naturally, therefore the aim was to mate the mare once in the period
of time between 24 hrs before ovulation to 12 hrs after ovulation. Mares were sometimes mated as early as 48 to
72 hrs before ovulation. For this reason mares were examined every 2 or 3 days during estrus and after covering,
to see if she has ovulated. With natural mating, the engorgement of the glans penis causes dilatation of the
cervical canal to several fingers diameter and sperm is deposited directly into the uterine body as the stallion
ejaculates through the patent cervical canal. If the cervix is particularly relaxed (such as in foal heat) the end of
the penis may even enter the uterus [14]. The fresh semen contains seminal plasma, which depresses the
endometrial inflammatory response to spermatozoa through its suppressive effect on PMN chemotaxis and
migration. [5, 6]. Therefore the pregnancy rates are generally considered to be higher when mated than when
inseminated with frozen semen [15].
Also when mated at least a day before ovulation, the oestrogen levels are maximal, progesterone levels are
minimal and therefore the uterine defence mechanisms and physical drainage should be optimal.
The only significant influence on pregnancy rate from the individual independent variables was age. This is in
confirmation with earlier studies [8]. Several can be the causes of the lower fertility in older mares; such as delay
in the first ovulation, a longer interovulatory interval, slower growth rate of the developing follicles, less
contractility of the uterus with fluid accumulation in the uterus as a consequence and the uterus of older mares
contains more inflammatory cell infiltrations, fibrosis and less glandular density [9]. Also in the present study,
especially the barren mares (table 5) showed an obvious decrease in pregnancy rates when age increases. Overall
pregnancy rate doesn’t differ significantly between the 3 status groups. This is in agreement with previous
publications [10]. In the present study maiden and foaling mares did also show a very little decrease in
pregnancy rates when age increases. However in the maiden mares group there was no mare older than 15 years
and only one mare in the 11-15 yr group. In the foaling group there were only 3 mares older than 21 yrs.
Maiden mares are younger mares, without conformational changes to the vulva and uterus. The uterine
environment should be in optimal form and the myometrial tissue is expected to be in good condition.
Sometimes though, older maiden mares have an abnormally tight cervix which fails to relax sufficiently during
oestrus so that fluid is unable to drain and accumulates in the uterine lumen. In many cases this fluid is negative
for bacterial growth and presence of neutrophils. Once the mare is mated the fluid accumulation will be
aggravated due to poor lymphatic drainage and impaired myometrial contraction compounded by the tight
cervix. The amount of intrauterine fluid will vary in individual mares ranging from a few millimeters to over
more than 5 cm in extreme cases. These older maiden mares do not normally have conformational changes, yet
histiological changes in endometrial tissue is seen. Endometrial biopsy samples reveal glandular degenerative
changes and stromal fibrosis (endometrosis) as a consequence of ageing despite the fact they have not been
mated or pregnant. [10]. It would be interesting to try distinguishing the treatment between older and younger
maiden mares. Table 4 does show higher pregnancy results in the 0-5 yr group than in the 6-10 yr group (76.9
and 57.1 % respectively), but in this case the pregnancy results may also be caused by the treatment (treated
24hrs has 75% pr) or by coincidence, because none of the results are significant. Only 20% of all the mares with
oedema score postpartum day 1 with < 0,5 mm was maiden mares, this decreased in the following two days to
15.1% and 13.1 % respectively. On the third day there no maiden mares with more than 0,5mm intrauterine
fluid. Post-partum fluid scores were also lowest in the maiden mares.
S.Bucca (2008) et al; [7] showed that the administration of 50 mg Dexadron IV (without other treatment)
directly before breeding did not give a statistically significant difference in pregnancy/cycle amongst treated
and control group. What they did find was significantly reduced oedema and fluid measurements after mating in
the group treated with 50 mg Dexadron IV. Mares used in this study were selected because of their
susceptibility to persistent mating endometritis.
Instead, Mc Donnell [12] failed to show any significant improvement in fluid, oedema or inflammatory
inhibition after administering 40 µg/kg body weight of dexamethasone before breeding time in experimentally
induced endometritis mares.
In the present study of all the 9 treated groups , slightly higher pregnancy results were seen in the group treated
24 hrs before mating , with exception of the foaling mares. In the foaling mare group no influence from the
treatment was seen at all, and the highest pregnancy rate was seen in the control group.
8
Most foaling mares were at their second cycle post partum following shortening the first post partum luteal phase
by the use of PGF2a. (Delayed) uterine involution is a restrictive factor on pregnancy result in this group
Ecbolics and uterine lavage are techniques to improve uterine involution, but the use of dexamethasone should
improve clearance and regeneration of mucilary flow as well. The results show that this hypothesis is not correct.
Although the foaling mares do have higher pregnancy rates than the barren mares, the non-treated control group
in the foaling mares has the highest pregnancy rates. Treated 24 hrs has an odds ratio of 1.062 of not getting
pregnant, which means there is almost no difference with the control group. The treated same day even has
higher odds of not getting pregnant (1.386). Foaling mares have intrauterine debris and fluid (even up to 2 weeks
post partum[17]), they could have developed anatomical and ⁄ or degenerative defects that interfere with uterine
drainage. Repeated breeding and foaling can cause anatomical defects ( poor perineal conformation, an
incompetent vagino-vestibular sphincter, vaginal stretching, an incompetent cervix or a low placed uterus or
more degenerative changes like an abnormal myometrium, periglandular fibrosis, vascular degeneration,
lymphangiectasia, scarring and atrophy of endometrial folds or damage to the mucociliary apparatus. [19]. These
postpartum fluid and debris are independent from the increase of fluid in early oestrus, oedema during oestrus or
physiological inflammation post covering. Therefore a corticosteroid may not help clearing the uterus and
oedema and fluid will accumulate. Uterine lavage and ecbolics (Oxytocin) have better influence on pregnancy
rates in foaling mares with intrauterine fluid [18] than the 10 cc of dexamethasone administered in this study,
but to confirm this a study with only dexamethasone treatment should be done.
In this study no difference was made between first cycle covers and other cycles, but pregnancy rates were
expected to be better in foal mares than barren mares, because expectation was that most barren mares are more
difficult to get in foal than the foaling mares in the first place. If we look at oedema and fluid scores postcovering, the foaling mares have highest percentage of fluid intrauterine, even after 3 days (independent of
treatment). More specific studies could be done to look whether mares covered in foal heat differ in fluid,
oedema and pregnancy results from the foaling mares in a later cycle.
Mares older than 16 yrs which were treated the day before had statistically significant odds ratios of 0.140 of not
getting pregnant (which means an odds ratio of 7.14 of getting pregnant). Older mares in general are considered
to have more problems than younger mares (see table 3), as mentioned before, they have problems clearing their
uterus before mating because of their lower myometrial contraction capacity , uterus position and vulvar
conformation [10]. If fluid before covering can be reduced by the help of dexamethasone, than this problem
older mares might be reduced. These results correspond with Barbacini et al.( 2003) [20], who reported that if
mares were treated to eliminate post-breeding fluid, only those older than 16 years showed decreased fertility.
Bucca at al.(2008) [7] found a significant reduction of endometrial oedema when dexamethasone was
administered at breeding time, the authors explained this event with a probable decrease in plasma concentration
of the immunomodulatory steroidal hormones cortisol and estrogen. According to Samper J.C. 2011 [11]
pregnancy rates increase when oedema at breeding time is lower. That result correlates with this study, because
when administered the dexametasone a day before covering the oedema is already low at mating time and
although not statistically significant, higher pregnancy rates are to be seen in the treated 24 hrs group. On the
other hand, this result does not correlate with Bucca at al.(2008)[7], who noticed significantly less oedema postcovering by administering the dexamethasone at the time of mating, but no significant improvement in
pregnancy rates. In this study a decrease of oedema was seen directly after administration of the dexamethasone
as well in the treated 24 hrs as in the treated same day group. The treated same day does not differ from the
control group and all three groups end in the same spot on day three after covering. The fast decline in the
treated 24 hrs group was based on only 3 measurements, which could be a coincidence as well. Day 1 is based on
57 mares and day -1 on 85 mares. The oedema in the treated same day group also decreases directly after
administration of the dexamethasone, but this decrease doesn’t differ from the decrease seen in the control
group. Based on all the p-values found (all the p-values from the control group and the treated same day group in
every test we did resembles a lot), there will not be a difference in the decrease of oedema. Also the decrease of
oedema correlates with physiological decrease of oedema in the end of oestrus, which means oedema would
have decreased anyway, apart from the dexamethasone treatment (see control group). This could explain the fact
that the decrease of oedema is not significant and correlates with Bucca’s explanation.
The dexamethasone-only treated group in A.M.McDonnel (1993) [12], showed the most consistent fluid
diameters in the uterine body, ranging from 20 – 24 mm post treatment (40 mg/kg bw dex-sodium sulphate on
day 12 of progesterone therapy - to simulate pre-eostrus, improve susceptibility to the establishment of infection
and therefore make the mares predisposed for endometritis).
9
In the present experiment, fluid increased in all three groups from one day before covering. The 24 hrs group
peaked at the time of mating, while we can see a peak on day 2 in the treated same day group and on day one in
the control group. Again only 1 measurement was available for the day of mating in the treated 24 hrs group.
In normal mares small fluid accumulations in early oestrus (pre-covering) appear to be correlated with a degree
of endometrial oedema. [1]. The correlation between fluid and oedema pre covering found in this study was not
significant.
Only the fluid after covering on day 2 showed a significance correlation (rho=0.175) with the oedema after
covering on day 2 (p= 0.036). But with a coefficient of determination of 4% no really assumptions can be made.
This is in disagreement with a previous study by Pycock and Newcombe [38], who did find a significant
correlation between fluid and oedema pre covering in their earlier study.
4. Conclusions
In this study we tried a very practical approach of increasing the pregnancy rates with help of the administration
of a glucocorticosteroid.. Every mare was selected randomly. Main goal was to achieve overall improved
pregnancy results.
Only age appeared to be a statistically significant influencing factor: older mares are more difficult to get in foal.
Only in mares older than 16 years the administration of 10 cc dexamethasone - isonicatinate 24 hrs before
natural cover seems to be correlated with higher pregnancy rates than without treatment. The cause of this can be
found in the fact that Voren tends to cause a direct decrease of oedema with as a consequence a decrease in
intrauterine fluid. Better clearance of the uterus before covering is achieved. Older mares are considered to have
more problems in clearing there uterus and they therefore benefit more from the dexamethasone.
Administration of the dexamethasone the same day (4hrs before – 4 hrs after) as mating did not seem to give an
improvement on pregnancy rate. These results resemble the non-treated control group results.
No difference in pregnancy result by status in general was seen. Maiden mares younger than 5 yrs had the
highest pregnancy percentages.
No influence of oedema pre- covering or fluid pre- covering on pregnancy results was found.
Dexamethasone gives a (non significant)decrease, on the amount of oedema, but does not give overall higher
pregnancy results in this study. It should be noted that the unlike previous studies, the present study did not only
use mares with a predisposition for post mating endometritis.
More specific research has to be done to find out the most optimal time for dexamethasone administration. For
now, only the mares older than 16 yrs seem to find a significantly positive effect from the 10 cc Voren
(dexamethasone) s.c. treatment administered around 24 hrs before naturally covered.
10
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