Housing, management and environment during farrowing and early lactation - The Gestating and Lactating Sow - page 221

also affect, either directly or indirectly, the release or activity of hormones that interfere
with the farrowing process.

During early pregnancy, after implantation of the embryos and developmental activity
of the corpora lutea, higher and constant concentrations of progesterone dominate the
hormonal pattern (Meulen et al. , 1988). This preserves the progress of pregnancy and, for
almost two thirds of pregnancy, the circulating concentrations of progesterone remain
high. At approximately 24 to 48 h before the beginning of parturition, the quick drop in
progesterone concentrations initiates a cascade effect on many other hormones, which had
quite stable concentrations throughout pregnancy. The concentration of prostaglandins
peaks, that of oxytocin increases and begins to exhibit high pulsating activity (Gilbert et
al. , 1994), prolactin concentration gradually increases, and that of estrogens, after peaking
quickly, gradually drops to basal levels (Anderson, 2000; Ellendorff et al. , 1979; Kindahl
et al. , 1982) (Figure 10.1). The period of farrowing is therefore linked to numerous large
hormonal changes taking place over a very limited time. Also, cortisol peaks at farrowing,
rising to 2-3 times the basal concentrations and then levelling down within 24-36 h
(Oliviero et al., 2008a; Osterlundh et al. , 1998).

10.3 Behaviour and activity

Before and during farrowing, the intense hormonal activity described above is
responsible not only for inducing the process of parturition, but also for triggering
visible behavioural changes. Activities such as rooting, pawing, turning and walking
increase considerably 24 h prior to farrowing (Hartsock and Barczewski, 1997) and
characterize the nest-building behaviour. One of the triggering factors of nest-building
behaviour was found to be a rise in prolactin (Castrén et al. , 1994), induced by a decrease
in progesterone and an increase in prostaglandins (Algers and Uvnäs-Moberg, 2007).
The external influence of the environment is also important for the expression of nest-
building behaviour. Indeed, the availability of proper nest-building material seems to
speed up this process (Damn et al. , 2000). Modern housing systems have promoted
the confinement of sows in crates during farrowing, whereby the sow has very limited
movement and bedding or any other nest-building substrate is often absent or very
limited. In these particular conditions, the nest-building behaviour triggered by
endogenous hormonal activity cannot be properly expressed. In the absence of a nest-
building substrate, confined sows express prolonged and unsuccessful nest-building
behaviour (Damn et al. , 2003). The lack of opportunity to express appropriate nest-
building behaviour can lead to increases in circulating cortisol and adrenocorticotropic
hormone (Jarvis et al. , 1997), which indicate a stressful condition. Gustafsson et al.
(1999) found that domestic sows were able to build nests identical to those of wild
boars, even after several previous farrowing experiences in confined crates without
bedding. This innate behaviour is therefore a clear indicator of impending farrowing
and is present regardless of housing or availability of bedding material.