Agriculture Reference
In-Depth Information
96 h) (reviewed by Soede and Kemp, 1997). Therefore, sows should be inseminated every
day of standing oestrus, to allow at least one insemination during the optimal interval.
Studies evaluating fertility after inseminations at either 12 h or 24 h intervals during
oestrus showed similar performance (Castagna
et al.
, 2003). However, specific attention
may need to be given to gilts, as they may have shorter optimal intervals (Waberski
et
al.
, 1994). As long as inseminations take place during oestrus, there is no major risk
of inseminating sows too early relative to ovulation. However, inseminating sows after
ovulation, may pose a risk of introducing sub-clinical infections (Rozeboom
et al.
, 1997),
thereby resulting in lower farrowing rate and litter size. These effects were shown to
be related to the rising progesterone concentrations that decrease uterine clearance of
infections (De Winter
et al.
, 1996). On the other hand, on a farm where more than 70%
of the sows received at least one post-ovulatory insemination, farrowing rate and litter
size were not affected (Castagna
et al.
, 2003).
17.5.2
Factors that affect the duration of oestrus
An earlier review (Soede and Kemp, 1997) listed factors that are known to affect the
duration of oestrus. Some major factors are mentioned below.
Boar contact
A greater stimulation with a boar increases the expression of oestrus and consequently
the duration of detected oestrus. This is true both in terms of the intensity/amount of
boar stimulation (e.g. bringing sows to a detection/mating area will increase the duration
of oestrus (Jongman
et al.
, 1996) and in terms of the frequency of oestrus detection
(Knox
et al.
, 2002). On the other hand, continuous boar presence may habituate sows
to boar stimulation and reduce the duration of detected oestrus, (e.g. Knox
et al.
, 2004).
It is therefore advised to house boars away from the sows and/or use another boar for
oestrus detection. Depending on the housing conditions of the sows, sows may be either
brought to the boar for oestrus detection or boars may be brought to the sows. In either
case, sows need to have good nose-to-nose contact with the boars during detection to
allow appropriate pheromonal and olfactory stimulation (Signoret, 1970). It is therefore
important to use mature boars (with appropriate boar smell) that are focussed on the
sows. Preferably, oestrus detection is performed twice daily to allow a good assessment
of the onset of standing oestrus, which is important for optimal timing of inseminations.
It is important to use the same oestrus detection protocol, as sows adjust their behaviour
to this oestrus detection protocol (Langendijk
et al.
, 2000a).
Stress
In 1970, Liptrap already showed that injections with ACTH and corticosteroids reduced
the duration of oestrus in pigs. Since then, many studies have confirmed the finding that
stressful conditions may inhibit oestrus expression in sows. Many different factors can be
experienced as stressful by sows. Major stressful factors are the social pressure between
sows, which may inhibit oestrus expression particularly in subordinate sows, and also
the fear of humans, which may reduce oestrus expression in sows in the presence of
