1. Introduction
The use of straw bedding in pig housing has a number of benefits to pig welfare, providing floor comfort, the opportunity for recreation and addition to bulk in the diet
Ž .
Arey 1993 , and is recommended by the Ministry of Agriculture, Fisheries and Food in Ž
. the UK MAFF, 1983 . The requirement for straw is different for pigs of different ages
and is dependent on their housing and husbandry conditions. Late pregnant and lactating Ž
sows use substrates, including straw, for nest building when housed in extensive Jensen, .
Ž .
1989 and intensive environments Lawrence et al., 1994 . There has been considerable research into the sows’ requirement for straw during the pre-partum period and this is
seen as an important issue owing to the widespread commercial use of farrowing crate systems that restrict freedom of movement and do not provide substrates for nest
Ž .
building Arey, 1997 . The increased maternal stress that may result from the use of farrowing crates could be owing to either an inability to access suitable substrates or
confinement or a combination of the two. The provision of straw or sawdust to confined Ž
sows could reduce their frustrated attempts to nest build Cronin et al., 1994; Arey, .
1997 . Under semi-natural conditions the pre-partum behaviour of sows involves distinct
periods of wandering, nest site selection and nest building, culminating in the creation of Ž
. Ž a protected nest in which to give birth to piglets. According to Jensen 1988
later .
developed in Jensen, 1989, and tested in Jensen, 1993 nest building is divided into two separate phases. The first phase of nest construction is regulated by internal factors and
involves preparation of the site, characterised by vigorous nosing, rooting and pawing. The second phase of nest building involves gathering and arranging of nest material and
is thought to be regulated by external factors, such as temperature, availability of
Ž .
suitable substrates and sensory feedback Jensen, 1993 . Ž
Sows induced to farrow by peripheral administration of prostaglandin F PGF ,
2 a 2 a
. Lutalyse typically show an initial period of nest building behaviour. This is followed,
some 12–24 h later, by a second more intense period of nest building, before the sow Ž
. gives birth to her piglets 22–36 h after treatment Widowski and Curtis, 1989 . In the
day preceding birth levels of the major metabolite of PGF , 13,14-dihydro-15-keto
2 a
Ž .
PGF rise in peripheral plasma Watts et al., 1988; Whitely et al., 1990 . Non-pregnant
2 a
gilts injected intramuscularly with PGF display nest building for at least 1 h after
2 a
Ž .
treatment Blackshaw, 1983 . The effect of PGF on nesting behaviour is specific to
2 a
post-pubertal females as PGF administered to boars results in displays of sexual
2 a
Ž .
behaviour Fonda et al., 1981 and PGF -treated juvenile pigs only show changes in
2 a
Ž .
activity and discomfort Widowski and Curtis, 1989 . We have previously shown that treatment of pseudopregnant gilts produces a consistent behavioural response on a stable
Ž .
endocrine background Boulton et al., 1997; Burne et al., 1999 . One advantage of using an artificial model of nest building is that the internal cue can be controlled to a much
greater extent than using pregnant animals, in which litter size and hormone secretion patterns can vary markedly.
We have previously shown that PGF -induced nest building is altered following
2 a
environmental disturbance. For example, PGF -treated gilts confined in farrowing
2 a
crates on bare concrete display very little nest building behaviour when compared with
Ž penned counterparts given access to straw, despite initial attempts to do so Boulton
. et al., 1997; Burne et al., 1999 . It is possible that nest building seen using the
PGF -induced nesting model is affected by the availability of suitable substrates, such
2 a
as an earth floor, straw, twigs and branches. However, PGF -treated gilts show similar
2 a
patterns of nesting behaviours, such as an increase in locomotion followed by increased pawing and rooting at straw, when housed on a concrete floor in a pen with straw
Ž .
Burne et al., 1999, in press , as they do when housed outdoors with access to an earth Ž
. floor, straw and other vegetation Gilbert et al., 2000 . Therefore, it may be that the
differences we have observed in PGF -induced nesting as a result of environmental
2 a
Ž .
disturbance confinement in a crate without straw are due to the complete absence of any nesting substrate.
The aim of this experiment is to investigate PGF -induced nesting behaviour in pigs
2 a
housed under the same conditions but with or without access to straw. We chose to use straw as a nesting substrate, rather than an earthen floor for example, because it is
inexpensive, readily available and widely used in commercial husbandry systems. Moreover, because most late pregnant sows in the UK are housed on concrete floors, the
provision of a wide range of substrates other than straw is simply not practical. A balanced design to test the hypothesis that straw has an effect on nesting behaviour
would require selecting pigs that have either been housed for long periods on a bare floor or provided with daily access to straw. However, we restricted this study to pigs,
which had been given daily access to straw. This experiment tested the hypothesis that acute removal of straw would alter the expression of PGF -induced nesting behaviour.
2 a
This would establish whether the PGF -induced nesting model is sensitive to environ-
2 a
mental feedback.
2. Methods
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