Agriculture Reference
In-Depth Information
compared with individually-housed sows. Although weaning-to-oestrus intervals were
short in both groups, the relative delay in oestrus and ovulation in the group- housed
sows may be related to the stress sows experienced from the mounting behaviour of sows
that were already in oestrus. Indeed, simulated stress during pro-oestrus (mimicked by
repeated adrenocorticotropic hormone (ACTH) injections) was shown to disturb follicle
development (Lang
et al.
, 2004), the LH surge and ovulation (Turner and Tilbrook, 2006).
Use of exogenous hormones
In groups of sows expected to show a low follicle development at weaning, such as first-
litter sows, exogenous hormones that mimick the actions of FSH and LH on the ovaries
may be used to stimulate follicle development. A well-known product to achieve this
combines 400 i.u. of eCG (equine chorionic gonadotropin, formerly known as PMSG
or pregnant mare serum gonadotropin) with mostly an FSH action, and 200 i.u. of hCG
(human chorionic gonadotropin) with mostly an LH action. When given at weaning or
the day after weaning, this hormonal combination led to improvements in the weaning-
to-oestrus interval in many studies but, sometimes, it resulted in lower pregnancy rate
or lower litter sizes (Kirkwood, 1999). On the other hand, Vargas
et al.
(2006) not only
found that more sows showed oestrus in the first 10 days following weaning when they
were treated 24 h post-weaning (95% vs. 80%), but they also had greater litter sizes in
the next parity (11.2 vs. 10.4). Culling rate over 3 parities was not affected. Differences
in reproductive performance between studies after this gonadotropin treatment may
be related to differences in follicle development at the time of injection. Therefore, if
exogenous hormones are given to stimulate post-weaning oestrus, it is advised to check
the consequences on litter size and farrowing rate in these treated sows.
17.4.2
Post-weaning follicle turnover
Epidemiological data have shown that a short weaning-to-oestrus interval is a risk factor
for the second litter syndrome. Indeed, sows with longer weaning-to-oestrus intervals
have a lower chance of producing a small second litter (Morrow
et al.
, 1992). It therefore
seems that follicle development, and thereby embryo survival, can be improved by
allowing sows a longer recovery period after lactation. This longer recovery period can
be achieved by inseminating sows at the second post-weaning oestrus or by feeding sows
a progesterone analogue during a shorter post-weaning period.
Skip-a-heat
Inseminating sows during the second oestrus after weaning instead of during the first
oestrus (skip-a-heat), allows sows to recover from lactation, which can have a major
impact on reproductive performance. Skipping the first oestrus of first-litter sows
improved their pregnancy rates by 15-17% and subsequent litter sizes by 1.3-2.5 piglets
(Clowes
et al.
, 1994; Vesseur, 1997; Werlang
et al.
, 2011). Clowes
et al.
(1994) showed
that sows at second oestrus had greater concentrations of IGF-1 and progesterone 50 h
after the LH surge, which may be indicative of better development of both the follicles
and the corpora lutea. When using the skip-a-heat approach, intense oestrus checking is
