Nursing behavior - The Gestating and Lactating Sow - page 291

a 'piglet-free' area, the nursing frequency is at least 10% lower (Arey and Sancha, 1996;
Pajor et al. , 2002) and the inter-individual variability in sow nursing behavior is larger
so that some sows even wean their litters prematurely (Bøe, 1993b). When suckling is
allowed to continue without human interference in semi-natural environments, nursing
frequency continues to decline until piglets are weaned at 10-16 weeks of age (Jensen,
1988; Jensen and Recén, 1989; Newberry and Wood-Gush, 1985).

There is a complex relationship between nursing frequency and milk production of the
lactating sow. Individual sows commonly increase or decrease their nursing frequency
from day to day without discernible external causes (Illmann and Madlafousek, 1995;
Špinka et al. , 1997). These spontaneous day-to-day changes in nursing frequency are
paralleled by changes in milk production (Špinka et al. , 1997). That is, if a sow increases
the number of nursings from one day to the next, the piglets get more milk on the next
day. This is due to the fact that mammary glands are almost completely refilled with
newly produced milk within 35 min after the last milk ejection (Špinka et al. , 1997), and
further milk accumulation then slows down asymptotically. If piglets succeed to suckle
more frequently, they get a greater number of almost-full-size milk portions and hence
greater total milk intake. Conversely, suckling at larger-than-usual intervals results in
a fewer number of portions and lower milk intake. A reduction in nursing frequency
may also lead to reduced prolactin concentrations and altered patterns of somatotropin
secretion (Rushen et al. , 1993), whereas more frequent nursings may lead to altered
insulin concentrations and, thereby, to a more catabolic state (Špinka et al. , 1999). hus,
the individual adjustments to nursing frequency can be seen as a bargaining between the
sow and the piglets to decide the amount of milk transferred (Špinka et al. , 2011) and,
thereby, the use of sow body reserves.

Beside the within-sow fluctuations of nursing frequency, there is also a degree of between-
sow variation in nursing frequencies (Špinka et al. , 2002; Valros et al. , 2002), and this
especially in later lactation (Wallenbeck et al. , 2008). In the first week of lactation, between-
sow differences in nursing frequencies do not seem to be related to milk production
(Špinka et al. , 1997), but later in lactation when sows differ in nursing frequencies because
of individual behavioral profile (Valros et al. , 2002), environmental factors (freedom of
movement, (Bøe, 1993a) or genotype (Meishan vs. European Large White, (Sinclair et al. ,
1998), greater litter weight gains are associated with more frequent nursings.

13.3.3 Teat massaging

Each nursing episode, from the nursing initiation when the litter assembles at the udder
and starts teat manipulation until the nursing termination by the sow or by the piglets,
lasts several minutes. With the exception of the brief milk ejection, the whole duration
of the nursing is devoted to piglet activity called teat massaging. During teat massaging,
a piglet alternates between brief sucking of the teat and intense rubbing of the teat
surrounding with its snout. The intensity of this tactile stimulation is often notable in
the contrast between the clean skin around the teats and the dirty body surface elsewhere.