Agriculture Reference
In-Depth Information
pattern to a high frequency/low amplitude pattern (Shaw and Foxcroft, 1985) (Figure 17.1).
The frequency of the LH pulses both before and after weaning is compromised in sows
with a more negative energy balance during lactation (Quesnel
et al.
, 1998; Van den
Brand
et al.
, 2000c), and this results in a prolonged weaning-to-oestrus interval (Quesnel
and Prunier, 1998; Shaw and Foxcroft, 1985; Van den Brand
et al.
, 2000c). Primiparous
sows therefore usually have smaller follicles at weaning (<2-3 mm vs. 3-4 mm), and
longer weaning-to-ovulation intervals compared with multiparous sows (e.g. (Gerritsen,
2008; Langendijk
et al.
, 2000c). While follicles are growing to ovulatory size, oestrogen
production from the follicles increases and LH pulsatility and FSH release gradually
decrease (Noguchi
et al.
, 2010; Prunier
et al.
, 1987). At a certain concentration threshold,
oestrogens induce an LH surge via positive feedback, which causes an immediate drop
in oestradiol production, induces ovulation and causes luteinisation of the follicle wall,
thereby triggering progesterone production. In pigs, ovulation takes place on average at
30±3 h (mean ± SD) after the peak of the LH surge (e.g. Soede
et al.
, 1994).
17.2.3
Oestrus and ovulation
Oestrus is the period around ovulation during which sows show receptive behaviour
characterized by the 'standing response' in presence of a boar. The sow stands immobile,
arches her back and cocks her ears (Signoret, 1970), thus allowing a boar to mate. Besides
Follicle selection
Follicle development
Inhibin
E
2
FSH
LH
Follicle atresia
Weaning
Ovulation
Figure 17.1. Regulation of follicular development in late lactating and weaned sows, showing the most
relevant reproductive hormones (picture kindly provided by and adapted from George Foxcroft, Edmonton,
Canada).
