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Author: N.M. Soede, P. Langendijk and B. Kemp
Introduction
Optimised insemination strategies on pig farms aim at reducing the number of
inseminations, without reducing reproductive performance. At the moment, one
insemination with good quality semen can result in good fertilisation results
when insemination takes place in a 24 h period before ovulation. However, knowledge
of this optimal period is not sufficient to limit the number of inseminations
to only one in all sows, because the time of ovulation of sows can not be predicted
within a 24 h range. Therefore, to optimise insemination strategies on farms,
either the period during which one insemination leads to optimal fertilisation
results must be increased and/or the prediction of ovulation time needs to be
improved. Much work concerning the timing of insemination -relative to oestrus
characteristics-and reproductive performance (litter size, farrowing rate) has
been performed in the sixties and seventies. Since the early nineties, ultrasound
has allowed assessment of the timing of ovulation in spontaneously ovulating
sows. Since then, experiments have increased our knowledge on the timing of
ovulation in sows relative to behavioural and physiological changes and on effects
of insemination strategies on fertilisation.
Besides the timing of insemination, also the circumstances around insemination
are important for fertilisation chances. In this overview, also recent data
on the role of boar presence on uterine motility are presented (Langendijk,
2001).
Optimal period between insemination and
ovulation
The life span of eggs after ovulation and the life span of a sufficient number
of sperm cells capable of fertilisation within the oviduct, limits the period
relative to ovulation in which inseminations can lead to successful fertilisation
(for review, see Hunter, 1994). Studies from the sixties already showed that
sows inseminated relatively early or late in oestrus showed a significant reduction
in fertilisation rate (Hancock and Hovell, 1962) and in litter size and farrowing
rate (Willemse and Boender, 1967). From these experiments, it is difficult to
draw conclusions about the fertile life span of sperm cells and oocytes, because
the time of ovulation varies considerably relative to the onset of oestrus (for
review, see Soede and Kemp, 1997). Therefore, in many experiments, the process
of fertilisation was studied using gilts with induced ovulation (e.g. Dziuk,
1970; Hunter, 1967; Hunter, 1981; Hunter et al., 1987). Those experiments showed
the importance of processes such as sperm transport, capacitation of sperm cells
and the filling and emptying of the sperm reservoir for the chances offertilisation.
In recent years, data have become available on the chances of fertilisation
relative to spontaneous ovulation. It was found that in some sows, optimal fertilisation
results can be achieved when insemination (with 3 billion sperm cells) takes
place between as many as 40 h before ovulation and 16 h after ovulation (Soede
et al., 1995a). However, to reach good fertilisation results in the majority
of sows, it was found that insemination has to take place in the 12 ((Waberski
et al., 1994a) or 24 h period before ovulation (Waberski et al, 1994b; Soede
et al., 1995ab; Steverink et al,. 1997) This is illustrated in Figure 1. Figure
1 shows the fertilisation rates as assessed at Day 5 after ovulation in about
300 sows in which insemination took place one with a dose of 3 billion sperm
cells. From those results, it is clear that fertilisation results are optimal
when insemination takes place before ovulation. In the period of 0 to 24 hours
before ovulation, the majority of sows have 100% fertilisation. Outside this
interval, the percentage of sows with partial fertilisation and of sows in which
none of the oocytes are fertilised increases considerably. Based on litter size
and farrowing rate, the optimal interval between insemination and fertilisation
was suggested to be even longer, between 28 h before ovulation and 4 h after
ovulation (Nissen et al., 1997). The fact that an interval of more than approximately
24 h results in a reduction in fertilisation rate means that the fertile life
span of sufficient numbers of sperm cells is limited to 24 h in the majority
of sows. The fact that inseminations after ovulation result in a reduction in
fertilisation rate means that the fertile life span of oocytes is about similar
to the time it takes for sperm cells to capacitate and reach the site of fertilisation.
Even in the optimal period, however, some sows have sub optimal or even no fertilisation
(see Figure 1).
Figure 1: Percentage
of sows having a fertilisation rate of 0%, 1-20%, 21-40%, 41-60%, 61-80%, 81-99%
and 100% after one insemination at variable intervals from ovulation. Insemination
was done with a dose of 3 billion sperm cells. Compiled data from Soede et al.,
1995ab and Steverink et al., 1997
In recent years, experiments have been performed that studied the period in
which inseminations lead to optimal fertilisation. Effects of the following
factors were investigated:
- Semen ageing during liquid storage; the use of aged semen reduced the
optimal period for insemination (Waberski et al., 1994b), although a semen
age of up to 38 h at insemination did not affect results (Soede et al.,
1995).
- Extender; negative effects of liquid storage on the optimal period for
insemination depend on the extender used (Waberski et al., 1994b).
- Semen dosage; a 6-fold increase in number of sperm cells (from 1 to 6
billion) hardly influenced the optimal period for insemination (Steverink
et al., 1997).
- Frozen semen; the use of frozen semen reduced the optimal period for insemination
to the period of 0-4 h before ovulation (Waberski et al., 1994a)
- Semen backflow during and after insemination; backflow during insemination
only affected fertilisation when a low semen dose (1 billion) was used and
backflow exceeded 20 ml (of 80 ml) (Steverink et al., 1998). Semen backflow
after insemination; no effect on fertilisation results (Steverink et al.,
1998).
In conclusion, from the above, it seems that factors reducing the number and/or
the quality of sperm cells that reach the oviduct, shorten the period in which
insemination results in optimal fertilisation. It can be concluded that good
quality semen of at most 2 days of age ensures good fertilisation rates when
inseminated between 0 and 24 h before ovulation. Strangely enough, a doubling
of the dose hardly had a positive influence.
From recent research, several indications exist that a further improvement of
sperm transport and/or sperm survival can be achieved. A few examples are given
of the possibilities:
- Increase in quality of semen ?
Except for motility, few in vitro semen parameters have found to be related
to fertilisation results in vivo (see Colenbrander, 2000). Recently, experiments
were performed in which the ability of (bull and boar) sperm cells to bind
to the zona pellucida or zona pellucida proteins was studied. Using boar semen,
Harkema et al. (1998) found that the percentage of sperm cells that show enhanced
binding to zona pellucida proteins in an IVF-medium after 3 hours of incubation
(presumed to be the capacitated sperm cells) reaches a plateau. The level
of this plateau varies considerably between boars (Harkema et al., 2002).
Four boars of which 31 %, 40 %, 45 % and 53 % of the sperm cells showed an
enhanced binding to the zona proteins after 3 hours incubation, had an in
vivo fertilisation rate (insemination immediately after ovulation with 0.5
billion sperm cells) of on average 77%, 82%, 87% and 94% of the oocytes, with
40%, 62, 67 and 83 of the sows having 100% fertilisation (Harkema et al.,
2002). Therefore, differences between boars in the percentage of sperm cells
capable of in vitro capacitation were positively related to in vivo fertilisation
results. It needs to be investigated whether this positive relation is also
found when insemination takes place well before ovulation and not after ovulation.
If a negative relation exists between the rate of in vitro binding to zona
proteins and the fertile life span of sperm cells in vivo, the average fertilisation
rate of the boars may be similar, which would not make this a useable tool
for selection of boars. However, in that case, a selective mixing of semen
of different boars might aid fertilisation results.
- Reduction of phagocytic ingestion
of sperm cells?
Sperm cells that do not reach the oviduct within an hour or so after insemination
are thought to be lost for the process of fertilisation due to phagocytic
ingestion by leucocytes. Rozeboom et al. (1999) showed that the rate of influx
of leucocytes into the uterine lumen is changed by the addition of seminal
plasma to the inseminate. Further, data show that phagocytic ingestion of
sperm cells by leucocytes is influenced by the composition of the inseminate
(Woelders, 2001). Therefore, manipulation of leucocyte influx and phagocytic
ingestion of sperm cells may lead to changes in the number of sperm cells
that reach the site of fertilisation and consequently fertilisation rate.
- Insemination procedure: (deep) uterine
insemination?
Especially when semen is costly, procedures to inseminate with low numbers
of sperm cells is important (e.g. sexed semen, semen of boars with a specific
genetic make-up). Deep-uterene insemination procedures have been developed
in laboraties in Spain (Martinez et al., 2001) and Germany (Rath et al., 1999)
and seem to result in pregnant sows with as few as 50 million sperm cells
inseminated. On farm trials with inseminations taking place cranial of the
cervix (but not deep uterine) suggest that this technique allows a reduction
in the sperm dose to 1 billion (Watson, 2001). However, disadvantages of the
current uterine insemination techniques are the limited use (older parity
sows only) and the need for more skilled staff.
- Sow characteristics?
Some indications exist that the fertile life span of oocytes differs between
breeds (Kemp and Soede, 1997), but little is known about the (sow) factors
that may influence e.g. capacitation rate, uterine activity, sperm transport,
or sperm survival in the reproductive tract. However, recently, information
has become available on factors affecting uterine activitity (see further).
Summarising, it seems there are several possibilities of further improvement
of transport and survival of sperm cells within the female reproductive tract.
These improvements may lead to either lower numbers of sperm cells in a semen
dose and/or an improvement of fertilisation results under otherwise suboptimal
insemination conditions (aged semen, inexperienced inseminators). The presence
of the boar during insemination also seems to be of importance in this respect
(see further).
Prediction of the time of ovulation
On average, ovulation takes place at 35 to 45 h after onset of oestrus (standing
response in presence of a boar). However, the variability between sows is large,
between e.g. 10 and 85 (Weitze et al., 1994) or 10 and 58 h (Soede et al., 1995a)
although sometimes less variation is found (35 to 43 h in 20 sows Mburu et al.,
1995). Also parameters such as vaginal temperature and vaginal mucus conductivity
have proven to be bad predictors for ovulation time (Soede et al., 1997; Stokhof
et al., 1996).
In a number of German, Dutch, Swedish and Danish investigations in the nineties,
the average timing of ovulation (percentage of oestrus) varied between 64% and
72% (see review by Soede and Kemp, 1997); the duration of oestrus (that is the
period in which sows show a standing response in presence of a boar) explained
50-60% of the variation in the timing of ovulation. At the moment, therefore,
the duration of oestrus seems the best estimator for the time of ovulation during
oestrus.
Unfortunately, the duration of oestrus is highly variable and gives only a retrospective
estimate of the time of ovulation.
Therefore, research should be aimed at finding other prospective estimators
for the time of ovulation.
In the course of estrus, responsiveness of the sow to stimuli applied to evoke
estrus behaviour (standing response) increases and decreases again (Willemse
and Boender, 1967). This means that early and late in estrus the sow will be
responsive to intense stimuli (e.g. a DMA (Detection-Mating-Area) or intensive
boar contact). When she is in the middle of the estrus period she is expected
also to be responsive to lower levels of stimuli (e.g BPT (Back-Pressure-Test)
in absence of boar). By applying different levels of stimuli during the course
of estrus different receptive phases may be distinguished (e.g. receptive to
BPT in absence of a boar, receptive to BPT when fence line contact with boars
is used or receptive to BPT when brought in a DMA). Langendijk et al. (2000b)
studied whether applying different levels of boar stimuli during detection of
estrus might distinguish more phases of responsiveness and whether this information
could be used to yield a more accurate predictor of ovulation. The results are
not very encouraging. A large percentage of sows will not show a standing response
at lower levels of stimuli at all during the course of estrus. Therefore, in
such sows different responsive phases during estrus can not be distinguished.
Moreover, even in sows showing more responsive phases during the course of estrus,
these phases were poorly related to the ovulation moment.
Possibly, a combination of parameters (maybe both physical and behavioural)
can give a better estimate of ovulation time than only one parameter. Such an
attempt was recently made by Langendijk et al. (1999b), who combined the redness
of the inner vulva to oestrous behaviour characteristics. In sows that showed
vulva reddening at the onset of boar oestrus (60% of the sows), the change from
red to pink occurred on average at 18 h before ovulation with a range from 36
h before to 2 h after ovulation. In their study, no hormone profiles were measured,
but it seems plausible that the change in vulva colour from red to pink is related
to the changes in the oestrogen profile. If these results prove to be repeatable,
it would mean that sows with a red inner vulva at onset of oestrus do not need
to be inseminated before the end of vulva redness, which would result in a more
efficient use of semen.
The ultimate prediction of ovulation time would be to be able to monitor the
rise in LH concentrations or the decline in oestrogen concentrations in a simple
way, but for pigs this may still be impractical. For the immediate future, possibilities
to ‘predict’ ovulation time are limited to the prediction of the duration
of oestrus for sows.
Towards more efficient insemination
strategies
The variation in oestrous behaviour and the related low predictability of ovulation
time makes it very difficult to inseminate sows in the optimal period before
ovulation using one insemination only. Therefore, most sows are inseminated
repeatedly during oestrus. One recurrent question is whether such repeated inseminations
should be performed at 12 h or 24 h intervals.
Lamberson and Safranski (2000) made an economical comparison between different
insemination schedules in combination with once or twice per day detection of
estrus. In their model, the likelihood of conception was set at a maximum of
90% (when insemination took place at ovulation) and dropped to about 62% with
insemination at 24 h before ovulation and also at 6 h after ovulation. Ovulation
was programmed to occur at 40±12 h after onset of oestrus and the weaning
to ovulation interval was set at 136±18 h. Using those parameters, economic
returns were calculated to be highest with inseminations at 12 h intervals;
at 12, 24 and 36 h after onset of oestrus with twice per day oestrus detection
and at 0, 12, 24 and 36 h after onset of oestrus with once per day oestrus detection.
These results are a logical result seeing the (relatively low) fertilisation
rates in the model for inseminations in the period of more than 12 h before
ovulation. Results from a survey on German pig farms showed that herds in which
sows were inseminated every 12 h did not have a better reproductive performance
than herds where sows were inseminated at 24 h intervals (VFV, 1999). Similarly,
Castagna et al. (2001) and Thorup (2001) also conclude from their experiments
that inseminations at 12 h and 24 h intervals can result in similar reproductive
performance.
These latter results more reflect results from fertilisation experiments as
mentioned before (Waberski et al., 1994b; Soede et al., 1995; Nissen et al.,
1996; Steverink et al., 1997) that clearly suggest that inseminations at 24
h intervals should be sufficient. However, it is clear that factors such as
inexperienced inseminators (Flowers, 1994) or the use of older semen (Waberski
et al., 1997) may cause the need for shorter intervals between inseminations.
Inseminating sows as often as possible may not just be a waste of semen, labor
and money, but may also have negative effects. Rozeboom et al. (1997) concluded
that a second insemination during late- or met-oestrus decreased farrowing rate
and litter size and De Winter et al. (1992) showed that uterine inoculation
with bacteria resulted in more uterine infections during late- or met-oestrus
than during early- or mid-oestrus. This phenomenon may be related to the oestrogen/progesterone
ratio, affecting both the blood circulation and therewith the influx of leucocytes
and the contraction activity of the uterus.
Therefore, very intensive insemination strategies can result in poor reproductive
performance due to infections when many sows are inseminated during late oestrus.
Use of knowledge of oestrus duration
Because ovulation takes place at a relatively fixed two-thirds of oestrus, a
prediction of the duration of oestrus is an indirect prediction of ovulation
and therewith of the optimal time for insemination. Unfortunately, the duration
of oestrus is very variable and seems to be influenced by many factors, such
as housing conditions, stress conditions, season, parity, genetic background
(see review by Soede and Kemp, 1997). Nevertheless, to some extent, prediction
of the duration of oestrus is possible. First of all, the average duration of
oestrus varies considerably between farms (from 31 to 65 h), but is highly consistent
from month to month within a farm (Steverink et al., 1999a), which implies that
the optimal timing of insemination during oestrus should vary between farms.
Second, it has been well established that the duration of oestrus is related
with the weaning-to-oestrus-interval (WOI) (e.g. Rojkittikhun et al., 1992;
Weitze et al., 1994; Kemp and Soede, 1996); sows with a short (3-4 days) WOI
on average have a long oestrus, associated with an advanced ovulation time (Weitze
et al., 1994; Kemp and Soede, 1996). Steverink et al. (1999a) found that this
relationship between WOI and duration of oestrus was significant in 43 (80%)
of 54 farms. As a consequence, on most farms sows with a WOI of 6 days or more
should be inseminated sooner after onset of oestrus to make sure that the first
insemination is before ovulation. The effects of the relation between oestrus
duration and optimal insemination time are illustrated in Table 1 for two farms
that differ in average duration of oestrus (Steverink et al., 1999b). The data
are generated with a simulation model for insemination strategies in pigs (PIGSIS;
Steverink, 1999). The simulation confirms that the timing of the first insemination
can easily be too late, especially on farms with a short duration of oestrus
and sows with a WOI of 5 to 6 days. Too early first inseminations are not really
a problem; sows can be inseminated again, but sows in which the first insemination
takes place after ovulation should be avoided. Therefore, to get insight in
the efficiency of the insemination strategy (and quality of oestrus detection)
on farms, farmers should establish the duration of oestrus and their farms,
and also taking into account the effect of Weaning-to-Oestrus Interval on the
duration of oestrus. This also enables checking of the appropriateness of insemination
timings of individual sows.
Table 1. Timing of first insemination
relative to ovulation 1 on
a farm with an average oestrus duration of 36 h or 60 h, simulated with PIGSIS
2 . On both farms,
sows are inseminated at 24 h after observed onset of oestrus and every 24 h
increase in Weaning-to-Oestrus-Interval is associated with a decrease in oestrus
duration of 6 h.
| |
Weaning-to-Oestrus
Interval (d)
|
|
|
4
|
5
|
6
|
|
Sows (%)
|
17.5
|
32.8
|
23.3
|
|
Farm oestrus duration:
36 h
|
|
|
|
|
Too early (%)
|
0
|
0
|
0
|
|
Correct (%)
|
55
|
37
|
21
|
|
Too late (%)
|
45
|
63
|
79
|
|
Farm oestrus duration:
60 h
|
|
|
|
|
Too early (%)
|
21
|
12
|
7
|
|
Correct (%)
|
66
|
68
|
68
|
|
Too late (%)
|
14
|
20
|
25
|
1 Too early: >24 h before
ovulation, Too late: after ovulation
2 PIGSIS: PIG Simulation
model for Insemination Strategies (Steverink, 1999)
Fixed-time AI
To improve the prediction of the timing of ovulation and therewith the possible
use of fixed-time AI, exogenous hormones (eCG, followed by either hCG or GnRH)
could be used. However, the success of these strategies appears to be very dependent
on the management system used (Brüssow et al., 1996). The use of these hormones
may mask poor management, is costly and it is not unthinkable that such a use
of ovulation-inducing hormones will be banned in a number of (EU-) countries in
the near future.
Role of boar presence during insemination,
with emphasis on uterine contractions
Besides the timing of insemination, also insemination conditions are important
for the success of the insemination, for example suggested to be related to their
effects on uterine contractions. Recent research has shed some (extra) light on
the effects of boar presence around insemination on uterine contractions.
In the sow, during mating sperm is deposited intracervically, and has to be transported
through both uterine horns to the oviduct, where fertilisation takes place. Porcine
uterine horns can be 1 to 1.5 m in length, and the intrinsic motility of sperm
cells can not be responsible for the short period of time in which sperm cells
have been observed to reach the oviduct (Viring, 1980). Especially when timing
of insemination is sub optimal (i.e. long before ovulation or after ovulation),
fast transport of semen to the relatively ‘safe’ utero-tubal junction
might be critical. Uterine myometrial contraction activity is believed to have
a function in transport of sperm cells from the uterine body to the oviduct. Therefore
it is believed that uterine contraction activity is important to get optimal fertilisation
results. In Figure 2, uterine contraction activity of a typical sow at different
phases of the reproductive cycle is shown.
Figure 2: Uterine
luminal pressure during 25 min recordings on different days around estrus for
one sow.
Arrows indicate contractions according to predefined criteria.
As in most mammalian species, myometrial activity in the sow increases around
estrus (Figure 3, Langendijk et al., 2001a).
Although all sows in the study of Langendijk et al. (2002a) showed an increase
in uterine contraction activity during estrus the variation between sows is substantial.
Frequency of contractions ranged from 6 to 40 h -1 , and the amplitude of contractions
ranged from 16 to 57 mmHg. These differences between sows were consistent over
the days around estrus, i.e. sows with a relatively high level of uterine activity
during the days before estrus also showed a relative high level of uterine activity
during estrus. It seems plausible that sows with relatively low uterine activity
also have an increased chance of suboptimal fertilisation results due to suboptimal
semen transport. From a review by Soede (1993) it can be concluded that specific
boar stimuli at or around the moment of insemination can influence reproductive
processes such as sperm transport and consequently affect fertilisation. Besides
external stimulation (like olfactory and tactile stimuli), also internal stimulation
(like sperm plasma or some of its components) is important. This paper will only
discuss effects of external boar stimuli on fertilisation of sows. Effects of
semen or seminal plasma components on fertilisation are reviewed by e.g. Claus
(1990) and Waberski, (1997).
Figure 3: Spontaneous
myometrial activity around estrus. Top: % sows with no myometrial activity; Bottom
left: average frequency of contractions for sows with myometrial activity; Bottom
right: average amplitude of contractions for sows with myometrial activity. Values
are averages and s.e.m. Values below X-axis are days to onset of estrus (D0 is
first day of estrus) and number of sows (Langendijk et al., 2002a). % inactive
myometrium Freq (per h) mm Hg
External boar stimuli are believed to exert their effects on uterine contraction
activity through a stimulation of acute central release of oxytocin. Oxytocin
is a smooth muscle stimulator. The sensitivity of the myometrium to oxytocin and
to stimuli that induce its release is probably high during estrus (Sheldrick and
Flint, 1985). Langendijk (2001) studied effects of different boar stimuli on oxytocin
release during estrus in sows. In their study they compared either BPT alone,
or BPT in combination with boar pheromone spray or BPT in presence of a boar.
Back Pressure Test with or without boar spray did not result in any changes in
oxytocin release. However, boar presence resulted in an acute and clearly pronounced
release of oxytocin (Langendijk, 2001). The fact that boar spray was not inducing
oxytocin release was not expected since Mattioli et al. (1986) found a release
of oxytocin after using boar spray. The absence of oxytocin release in response
to only BPT was confirmed by Mathiasen (2001) although in their study, the boar
was housed next to the sows. He further showed, that intense human stimulation
(a BPT in combination with manipulation of the abdominal, inguinal, pelvic area
and the area under the vulva),again using sows that were housed next to boars,
could result in release of oxytocin. The levels of oxytocin release were however
lower than with full boar exposure. It appears therefore that full boar contact
induces oxytocin release in sows but the effects of lower levels of stimuli (or
fewer stimuli) on oxytocin release are less clear. Langendijk (2001) also studied
effects of different boar stimuli on uterine contraction activity during estrus.
Tactile stimuli, boar pheromone and boar presence caused only a slight increase
in frequency of contractions and a slight increase in mean amplitude of contractions.
However, in those cases in which the spontaneous uterine activity was low (frequency
of contractions <26 h –1 ; ca 50 % of the sows), boar presence clearly
increased frequency of uterine contractions (+ 7 h –1 ), in contrast to tactile
and pheromone stimulation (P < .05). From this one can conclude that boar presence
during insemination will stimulate uterine contractions in sows which have weak
uterine contractions before stimulation.
Can artificial insemination in itself stimulate uterine contractions? Claus and
Schams (1990) found no oxytocin release after insertion of an insemination catheter
and Langendijk et al. (2002a) showed that uterine infusion with physiological
saline did not increase uterine contractions. However, in a recent study at our
laboratory, artificial insemination of 80 ml of a standard insemination dose increased
uterine contraction frequency by 50%. Additional use of a mating clamp mimicking
the pressure on the flanks of sows during mating proved unsuccessful in inducing
extra uterine contraction activity. Also, leaving the catheter in the cervix for
an additional 5 min while regularly moving the catheter did not result in extra
contractile activity.
Summarising, the data suggest that boar presence during insemination positively
influences uterine contraction activity especially when the contraction pattern
of a sow is low. Using components of boar presence like BPT, mating clamps or
BPT plus boar spray is not as effective as the whole boar. Therefore it is advisable
to use a boar in front of the sow during insemination.
Table 2 Effects of intra-uterine
infusion of 40 ml saline with 1 mg prostaglandins at 10 minutes before insemination
(40 ml; 0.5x10 9
sperm cells), on backflow of semen during insemination and on fertilisation results
(based on Langendijk et al., 2002b)
|
|
|
Control
(n=16)
|
Cloprostenol
(n=18)
|
|
Backflow
1
|
None
|
11 (69%)
|
3 (17%)
|
|
|
Little
|
3 (19%)
|
9 (50%)
|
|
|
Much
|
2 (13%)
|
6 (33%)
|
|
|
|
|
|
|
Median fertilisation rate (%)
|
81a (0-100)
|
21b (0-100)
|
|
Median accessory sperm cells (n)
|
2.1a (1-21)
|
0.8 b (0-19)
|
|
|
|
|
|
1 The distribution
of the animals over the categories of backflow differed between treatments (P<0.05)
ab P<0.05
Not only oxytocin, but also prostaglandins can stimulate myometrial activity.
Field trials in which ocytocin or prostaglandins are injected in sows during insemination
or used in the insemination dose seem to indicate that these treatments may improve
reproductive results in sub optimal conditions (Levis, 2000), for example when
inseminations are performed by inexperienced inseminators (Flowers, 1995), when
using old semen (Flowers, 1996) or during summer infertility (Pena et al. 1998a,b).
However, there are some indications that overstimulation of contraction activity
may also occur, resulting in a lower reproductive performance (Langendijk et al.,
2002b; see Table 2). In their study, sows were infused intra-uterine with either
40 ml of saline (control) or with 40 ml of saline containing 1mg cloprostenol
(prostaglandins) at ten minutes before insemination (40 ml; 0.5x10 9
sperm cells). Ovulation was timed with GnRH (50 mg at 85 h after weaning) and
insemination took place at 20 h before expected ovulation (at 40 h after GnRH-injection
on average). In Table 2, effects on backflow of semen and on fertilisation results
are shown. The prostaglandin treatment was earlier shown to increase uterine contractions
(Langendijk et al., 2002a), but was now found to also increase backflow of semen
during insemination and resulted in lower fertilisation results. Apparently, uterine
contractions can be stimulated to such an extent that negative effects on sperm
transport and consequently, fertilisation results can be expected. From the studies
in which effects of treatments were assessed it appeared that, at the applied
dosage, prostaglandin treatment increased uterine contractions in all the sows,
irrespective of their spontaneous uterine activity (Langendijk et al., 2002a),
whereas oxytocin (either by infusion (5 IU) or due to boar presence) seems to
stimulate contractions especially in sows with low spontaneous activity. Therefore,
stimulation of the myometrium seems beneficial as long as contractility does not
exceed a certain level. In this respect, boar presence and treatment with lowe
levels of oxytocin are probably a safe way to stimulate uterine contractions.
Final remarks
The choice for a more efficient insemination strategy (that is, a decrease in
number of inseminations per oestrus) depends on e.g. labour costs of insemination,
costs of an insemination dose or costs of boars on the one hand and on e.g. labour
costs for oestrus (ovulation-) detection on the other hand. The balance between
these costs can change and for example the application of frozen semen, of sexed
semen, or of semen from boars with a specific genetic makeup may increase the
demands for more efficient insemination strategies. Therefore, research should
continue to be focused on extension of the period in which an insemination leads
to optimal fertilisation results and the predictability of ovulation time and
on efficient delivery of inseminated sperm cells to the site of fertilisation.
From the data present in this paper it is clear that use of boars during estrus
detection and presence of boars during insemination is highly advisable. Generally
one can say that using only components of boar stimuli (BPT or boar spray) gives
limited effects as compared to full boar exposure. Probably there are differences
between boars in effectiveness to stimulate the above mentioned processes. There
is some evidence that there are boar effects on the duration of oestrus of sows
(Soede and Kemp, 1997). It is known that boars should be at least 11 month old
to be able to induce estrus in gilts (Kirkwood and Hughes, 1980). Probably from
a behavioral point of view boars need to be active and enthusiastic in their interaction
with sows. Turner et al. (1996) showed that the level of sexual motivation of
boars does not influence the efficiency of detecting hormonally induced estrus
using the BPT in ovariectomized gilts. However, sexual motivation of the boars
was scored as number of copulations in a mating test and reaction time before
first mating. One can question if this parameter is an accurate one to select
boar for. Further research on parameters to select boars for good estrus detection
is needed.
Wageningen University, Department of Animal Sciences, Animal Husbandry Group,
Marijkeweg 40, 6709 PG Wageningen, The Netherlands, e-mail: Nicoline.Soede@genr.vh.wau.nl.
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Author: N.M. Soede, P. Langendijk and B. Kemp
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