Nursing behavior - The Gestating and Lactating Sow - page 295

served the purpose to keep a limit on allo-suckling, i.e. non-offspring nursing. In free-
ranging and group-housed sows, piglets allo-suckle either by permanently switching to
another dam, or by opportunistically suckling on other sows while staying at their own
mother for regular suckling. When nursings are tightly synchronized, the opportunity
for allo-suckling is reduced, since the opportunistic allo-sucklers cannot suckle both
their own mother and another sow at the same time (Illmann et al. , 2005; Maletínská
and Špinka, 2001).

13.4 Functions of nursing/suckling behavior during the

course of lactation

The functional view of nursing behavior has its roots in evolutionary theory. It is based
on the assumption that animal behavior has been shaped by natural selection so that
it brings the behaving animals benefits such as food, security, information, etc., which
in turn contribute to the animals' survival and reproduction. Applying this view to the
behavior of domesticated animals is not without controversy since both the animals
and the environment are often quite different from their wild ancestors in their natural
environments. For instance, the domestic pig differs from the wild boar in that it has
much larger litters, is generally less active (Gustafsson et al. , 1999), is given free food,
and its physical and social environments are determined and provided by humans.
Nevertheless, the basic functional question 'What benefit does this behavior bring to the
animal?' proved fruitful in behavioral research on domestic animals in the last decades
(Drake et al. , 2008; Fraser et al. , 1995; Puppe and Tuchscherer, 2000; Špinka et al. , 2011).

Nursing provides the young with milk. The rich structure and dynamism of the sow-
piglet, piglet-piglet and sow-sow interactions imply that nursing is much more than a
mechanical transfer of milk from the sow mammary glands to the offspring's stomachs.
The nursing interactions co-determine how much milk is provided, how this milk
production is allocated to individual piglets, and how the milk provision to non-
maternal young is prevented/ regulated. These mechanisms can be seen as results of
interactions between the strategies of the individual actors, i.e. the sow and the piglets.
From the perspective of the sow, the best strategy is to support the survival and growth
of as many progeny as possible. However, if some of the piglets are not viable or the
resources available for the sow cannot support all the progeny, it may be beneficial for
her reproductive success to discard some of the progeny early and be able to provide
more milk to the remaining healthy young. Also, if the sow uses up a lot of her body
reserves during lactation or is suckled by heavier piglets, her future reproduction may be
compromised. For example, the weaning to estrus interval may be prolonged and the next
litter size decreased (Bierhals et al. , 2012; Schenkel et al. , 2010; Ten Napel et al. , 1995).
Thus, within the nursing interactions there are features showing cooperation between
the mother and the litter to ensure efficient milk transfer, but there may also be features
reflecting the parent-offspring conflict about how many progeny to raise and how much
to invest into them so that future reproduction is not compromised.