Reproduction performances and conditions of group-housed non ...

- Appendix 1 -
they are mature i.e. capable of fertilisation (see above). The fertilisation ability of the sperm
in the female tract begins to decline after 12 hours (Dziuk, 1970) but can survive for more
than 44 h (Kemp & Soede, 1997). Therefore a successful insemination or mating also de-
pends upon clear oestrus behaviour of the sow and a co-ordination between oestrus behav-
iour and ovulation, which as will be discussed later, depends on a good hormonal function.
Physiological events after mating/insemination
To gain pregnancy and a high litter size, the embryo survival also has to be high. A high
embryo survival depends upon whether the following events are successful.
Fertilised eggs are moving from the ampullary-isthmic junction (where fertilisation occurs)
to the uterus. During this journey, which takes about 48 h, the eggs under go cleavage (cell
division) and when they reach the uterus, they are at the four-cell stage (Dziuk, 1985;
Ashworth, 1991). In the uterus the cell divisions continue (Hughes et al., 1996). On day six
to day seven hatching from the zona pellucida (which is a complex glycoprotein matrix
formed around each oocyte during follicular development (Dunbar & Bundman, 2003) occurs
(Stroband & Lende, 1990). After hatching, the eggs become increasingly dependent
upon nutrients in uterine secretions (Ashworth, 1991). Between day 7 and 12 of pregnancy
the fertilised eggs redistribute themselves over the full length of both uterus horns (Dziuk,
1985). Finally the elongation and the implantation (attachment to the uterine endometrium)
take place. Elongation starts around day 10 of gestation (Ashworth, 1991; Geisert & Yelich,
1997). During elongation the embryos undergo a morphological change from 10 mm
spherical (i.e. round) to tubular (20-40 mm) and finally filamentous (up to 100 cm in
length!) shapes by day 14-16 (Ashworth, 1991; van der Lende et al., 1994; Geisert & Yelich,
1997). The implantation starts around day 13-14 of pregnancy and is completed about
24 days after fertilisation (Crombie, 1970; Ashworth, 1991). Each embryo is surrounded by
separate fluid filled membranes, the amnion and chorion, which form the placenta
(Ashworth, 1991). From day 18 to day 30 of pregnancy the volume of this fluid increases
markedly (Ashworth, 1991) and it is the presence or absence of this fluid that can be detected
by the commonly used ultrasound pregnancy diagnosis instruments. On day 35 of
pregnancy the embryo is approximately four cm long (van der Lende, 1989) (see Figure 2).
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