Agriculture Reference
In-Depth Information
oten not noted and such sows will thus be marked as 'delayed oestrus. On the other hand,
stimulation of lactational ovulations can be a management strategy to allow lactational
inseminations (see further).
17.3.3
Number of piglets - split weaning
Split-weaning involves the permanent removal of a part of the litter a few days before
complete weaning. It reduces the suckling stimulus of the piglets in late lactation and
the energy balance of the sows is therefore improved. In the different studies reported,
there were considerable variations in the split-weaning regimes. Split-weaning lasted for
3 to 7 days before complete weaning, leaving 2 to 6 piglets for the remaining lactation
which lasted 17 to 35 days. Matte
et al.
(1992) reviewed the reproductive performance
of split-weaned sows and concluded that the reduction in the interval from weaning to
oestrus was largely affected by the number of piglets that remained with the sow during
the last days of lactation. The greatest reduction in weaning-to-oestrus interval was seen
when only 3 piglets remained with the sow for the last 4.7 days. Interestingly, Grant (in:
Varley and Foxcroft, 1990) showed that the effects of split-weaning (leaving 5 piglets
with the sow for the last 7 days of lactation) on both LH concentrations and follicle
development were larger when the 6 anterior teats had been covered compared with when
only split-weaning was applied. Since piglets had a similar growth rate in both treatments,
and thus the metabolic demands on the sows were similar, it appears that effects on LH
and follicle development are primarily mediated by the neural stimulation of suckling.
Only few experiments have since evaluated the effects of split-weaning on reproductive
physiology or performance of sows and these have all focused on lower parity sows
(Mahan, 1993; Vesseur
et al.
, 1997; Zak
et al.
, 2008; Foxcrot
et al.
unpublished results).
These studies also consistently show that the weaning-to-oestrus/insemination interval is
reduced when split-weaning is applied. Two more recent studies have evaluated the role
of the endocrine status on this effect. Degenstein
et al.
(2006) showed that during the
whole period of split-weaning (days 16-19 of lactation), concentrations of prolactin were
reduced and those of FSH were increased. Zak
et al.
(2008) also found an acute increase
in LH concentrations and pulse frequency in the 10 h following split-weaning on day 18
of lactation. At weaning (3 days later), average LH concentrations were similar to those
of the control animals. The day after weaning, split-weaned sows had more follicles with
a diameter larger than 3 mm. Thus, the increased LH and FSH concentrations during the
split-weaning regime, and possibly the lower prolactin concentrations, stimulated follicle
development and shortened the weaning-to-oestrus interval.
Hardly any information is available on the fertility of split-weaned sows. However, the
reproductive characteristics that have been measured show a slightly increased ovulation
rate (17.7 vs. 15.5 (Zak
et al.
, 2008)), a similar embryo survival rate on day 28 (64 vs. 60%
(Zak
et al.
, 2008)); similar subsequent litter sizes (Vesseur
et al.
, 1997), and increased
farrowing rate in parity 2 sows (97 vs. 86% (Vesseur
et al.
, 1997)). Thus, removing the
majority of the litter for the last 3-5 days of lactation consistently shortens the weaning-to-
oestrus interval through a stimulation of follicular development, primarily by a reduction
in the suckling stimulus. Yet, this improvement in weaning-to-oestrus interval is only
seen in groups of sows which would otherwise have an extended weaning-to-oestrus
