Agriculture Reference
In-Depth Information
interval. Furthermore, the few papers that have investigated the effects of split-weaning
beyond the post-weaning oestrus are not very conclusive so that overall, its effects on
subsequent fertility remain unclear. These results also imply that small reductions in the
number of piglets during lactation often do not have a major influence on subsequent
fertility, partly because the remaining piglets will consume more milk on an individual
basis (Vesseur
et al.
, 1997).
17.3.4
Intermittent suckling and lactational ovulations
One way to reduce the suckling stimulus of the piglets and, as such, stimulate follicular
development and subsequently lactational ovulation, is to introduce daily periods of
separation of sows and their piglets during the last part of lactation. This procedure
is termed reduced or limited suckling, interrupted suckling, or intermittent suckling.
Langendijk
et al.
(2007) and Gerritsen
et al.
(2008) reviewed the effects of intermittent
suckling on subsequent fertility. They showed that up to 90% of sows may show lactational
oestrus if the intermittent suckling does not start too early in lactation (preferably later
than day 18) and lasts for at least 10 h per day. During separation, sows should be housed
out of sight and hearing from the piglets, preferably allowing some boar contact. The
genotype of the sow is of major importance and also the parity, since primiparous sows
have a lower oestrous response to intermittent suckling (Soede
et al.
, 2012). Interestingly,
sows that respond to the treatment by showing oestrus do so in a synchronous fashion at
a seemingly normal interval of 4 to 5 days from the onset of treatment (see Gerritsen
et
al.
, 2008). As a consequence, a treatment period of 14 days compared with 7 days did not
increase the occurrence of an oestrous response and sows that did not show a lactational
oestrus had a 'normal' weaning-to-oestrus interval once they were weaned (Soede
et al.
,
2012). Thus, the lactational oestrous response of sows in an intermittent suckling regime
seems to be an 'all or none' phenomenon, with either a 'normal' duration of the follicular
phase or no response at all (Stevenson and Davis, 1984).
In early studies on intermittent suckling, the majority of sows ovulated after weaning. Thus,
from those studies it remains unclear if and how intermittent suckling and/or lactational
inseminations affect the pregnancy outcome. More recent intermittent suckling studies
(reviewed by Gerritsen
et al.
(2008), suggest that pregnancy rate, embryo survival and
embryo development are negatively affected if the intermittent suckling-induced ovulation
takes place as early as 19-21 days after farrowing and if intermittent suckling continues
until 20 days after ovulation. This latter effect may be related to the lower progesterone
concentrations in these sows. When sows are inseminated more than 3 weeks after
farrowing and intermittent suckling stops 2 days or 9 days after ovulation, neither litter
size nor farrowing rate are negatively affected by lactational inseminations (Soede
et al.
,
2012). Similarly, inseminations performed during lactation do not negatively affect litter
size or farrowing rate when performed more than 3 weeks after farrowing (Gaustad-Aas
et
al.
, 2004). In systems with extended lactation periods, it might be economically attractive
to inseminate sows during lactational ovulation. Recent studies have therefore evaluated
the influences of group housing (Hultén
et al.
, 2006), daily boar contact, bringing sows to a
detection/mating area (van Wettere
et al.
, 2013) or daily fence line boar contact combined
with split weaning (Terry
et al.
, 2013) to stimulate lactational ovulations.
