Agriculture Reference
In-Depth Information
After the brief milk ejection, piglets resume teat massaging and may continue to do so for
several minutes, although their number decreases as they individually cease to be active
at the udder. This is the post-ejection massage phase. Nursing termination is triggerred
either by the piglets, when they fall asleep at the udder or leave to rest elsewhere, or by
the sow when she rolls on her belly or stands up while the piglets are still active with
post-ejection massage.
During a suckling, the sow emits regular deep grunts at a rate of about one grunt every
two seconds during the pre-ejection massage. About 20 sec before milk ejection, the
grunt rate suddenly increases to a peak of about two grunts per second, and then wanes
(Illmann
et al.
, 1999).
13.3.2
Nursing frequency
Sows nurse every 50 min on average with a wide variation in the individual inter-nursing
intervals. There is little or no difference in the nursing rhythm between day and night. The
nursing rhythm is related both to the physiology of milk release, and to the interactions
between the sow and the litter. After each milk ejection, there is a refractory period
of about 20 min during which it is impossible to trigger another milk release through
teat stimulation, no matter how intensive. The inhibitory system is centrally located as
intravenous injections of oxytocin can cause gland contraction within a minute of the
natural milk ejection (Ellendorff
et al.
, 1982). The other factor causing the rhythmic
nursing is the cycle of activity and resting in the piglets. After ingesting milk and the
post-ejection massage, piglets mostly become inactive or go asleep, either at the udder
or at the most comfortable resting place available, and it is usually after several tens of
minutes that they are active again at the udder and start a new nursing episode.
Nursing initiation is the decisive factor for nursing frequency. During the first days
after parturition, the sow initiates 80 to 100% of the nursings. During the second week
of lactation, this proportion drops below 50% and by 4 weeks of age, less than 10% of
nursings are sow-initiated (Algers and Jensen, 1985; Castrén
et al.
, 1989b; Jensen
et al.
,
1991; Šilerová
et al.
, 2006).
The nursing frequency changes gradually over the course of lactation, but changes are
relatively minor within the first 4-6 weeks. From the initial 24-26 nursings per 24 h, there
is a slight increase to 28-30 nursings per day until the second week of lactation and a
slow decline thereafter. From the second week on, sows attempt to limit piglets' suckling
activity in several ways possible, i.e. by spending more time resting on their sternum
or by declining to lie down/roll on their side when piglets ask for teat access through
activity at the udder (Valros
et al.
, 2002). Nevertheless, even around commercial weaning
age at 4-5 weeks, sows still nurse almost 20-24 times a day (Valros
et al.
, 2002). he
nursing frequency seems to follow the same pattern over the first four weeks of lactation
in very different housing systems and environments, ranging from the commercial crate,
to individual and group pens and semi-natural free-ranging (Jensen and Recén, 1989;
Newberry and Wood-Gush, 1985; Pajor
et al.
, 2002; Šilerová
et al.
, 2013; Wallenbeck
et
al.
, 2008). However, in systems where the sow can leave the piglets behind and access
