1. Introduction
In commercial conditions, the daily energy supply to sows during pregnancy is determined in order to meet the requirement for maintenance, uterine growth and
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maternal gain AFRC, 1990; Noblet et al., 1990 . In fact, the feeding level is adjusted in order to maintain optimal body condition of sows during successive parities and
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maximize their longevity Dourmad et al., 1994 . Consequently, sows are generally restricted fed during pregnancy to a level which amounts to only 50 to 60 of their
voluntary food intake, inducing sustained feeding motivation during most of the day Ž
. Lawrence et al., 1988; Hutson, 1991 . The behavioural expression of feeding motiva-
Ž tion has been recorded from various parameters Lawrence and Terlouw, 1993; Rushen
. Ž
. et al., 1993 including the feeding rate Terlouw et al., 1991; Brouns et al., 1994 and
Ž the level of stereotypic behaviours expressed by sows around meal time Rushen, 1984;
. Robert et al., 1993 . Operant conditioning techniques, used to assess needs andror
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preferences of farm animals Kilgour et al., 1991 , have also been developed to examine Ž
. feeding behaviour. In pigs, Lawrence et al. 1988 demonstrated that feed restricted
boars sustained a high level of feeding motivation, as measured by an operant condition- ing procedure.
The energy dilution of diets by fibre allows the bulk of food eaten by sows during Ž
pregnancy to be increased without changing the daily energy intake Shi and Noblet, .
1993 . It has been previously shown that sows fed high-fibre diets perform less Ž
. stereotyped behaviours Robert et al., 1993; Brouns et al., 1994; Ramonet et al., 1999a
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and more resting behaviour Robert et al., 1993; Ramonet et al., 1999a . High-fibre diets have also been shown to reduce feeding motivation measured by operant conditioning
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tests, especially in the immediate post feeding period, in growing pigs Day et al., 1996 Ž
. and in fed restricted sows Robert et al., 1997 .
Nevertheless, the effect of specific feedstuffs on feeding motivation of food restricted sows is still unclear. In sows fed ad libitum, the nature of the fibrous ingredients has an
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effect on feed intake and time spent in feeding activity Brouns et al., 1995 . In particular, sows fed sugar beet pulp-based diet showed limited spontaneous feed intake
which should be interpreted as a reduced feeding motivation. The aim of this study was to evaluate the incidence of the level and the nature of
fibrous component in diet on the feeding motivation of pregnant restricted fed sows. This was achieved by comparing a low and two high fibre diets differing in their
physico-chemical properties, which have an influence on the profile of metabolic and digestive processes. The potential effects of the fibrous diets were measured after a
medium and a long-term period in order to evaluate the feeding motivation of sows over the day.
2. Materials and methods
2.1. Animals and housing Multiparous Large–White sows were used in the experiment. Three weeks after
mating, the sows were moved into two experimental rooms and housed individually in
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stalls 0.60 = 1.90 m with a concrete floor and wood shaving litter in the dunging area. Rooms were cleaned daily in the morning at 0930 h and, fresh litter was supplied.
Artificial lighting was provided from 0815 to 2015 h, and ambient temperature was kept at 18
8C28C. During the first week of the experiment, sows were adapted to the experimental room, and received 2.4 kg per day of a standard diet. Each sow was then
fed the three experimental diets during three successive 3-week periods according to a 3 = 3 Latin square design. Sows were weighed at the beginning and at the end of each
experimental period.
2.2. Diets The experimental diets were formulated, and daily feed allowances were calculated in
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. order to provide the same daily intake of metabolizable energy ME
33.4 MJ per day . All daily rations contained a common base including the same amount of wheat,
sugarcane molasses and soybean meal. This base provided about 60 of the daily Ž
. energy intake. Only one feedstuff made up the remainder of the ration Fig. 1 . The S
diet contained no extra source of fibre over the level present in the common base, the supplement of energy and protein of this diet being provided by corn starch and soybean
isolate. In the BP diet, the major fibre was sugar beet pulp, which is rich in soluble fibre
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and characterised by a high water-holding capacity Cherbut et al., 1994 , and a high Ž
. digestibility in pigs Shi and Noblet, 1993 . In contrast, the WB diet was formulated
with wheat bran, a feedstuff with a low water-holding capacity and less digestible to pigs.
Fig. 1. Composition of the experimental diets.
Ž The level of fibrous components and energy content differed between diets S diet: 21
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g crude fiber CF , 88 g neutral detergent fiber NDF and 15.3 MJ ME per kg dry Ž
. matter DM ; BP diet: 93 g CF, 247 g NDF and 13.7 MJ ME per kg DM; WB diet: 47 g
. CF, 213 g NDF and 13.5 MJ ME per kg DM . The water-holding capacity was 1.78,
4.31 and 2.91 g water per g DM for S, BP and WB diet, respectively. To provide the same daily energy supply, sows received 2.44, 2.74 and 2.90 kgrday of S, BP and WB
diet, respectively. Diets were supplied in pellets in a single meal given at 0930 h. Water was available ad libitum.
2.3. Operant conditioning During the week of adaptation to the stall, sows had been trained to perform operant
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conditioning tests during three consecutive days learning sessions . Thereafter, all sows were re-trained during the 11th day of the 3-week period, in order to check and reinforce
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the operant conditioning procedure training sessions . During training session, sows had to press the switch until they reached the fixed ratio of 10 presses per reward. The
apparatus used during training and testing consisted of a blue switch fixed near the sow’s feed trough and a reward delivery device placed above the trough. The manipu-
Ž landa and the reward device were connected to a microcomputer Macintosh II, Apple
. Computer via a custom-built interface, controlling delivery of rewards and recording
the time at each switch push. Software designed at the INRA Pig Research Station, enabled a variety of reinforcement schedules to be imposed. During learning sessions,
Ž sows were trained according to procedures used in previous studies Lawrence et al.,
. Ž
. 1988; Lawrence and Illius, 1989 , in a fixed ratio schedule FR through a series of 1, 3,
5, and 10 button presses for 8 g food rewards. The number of presses necessary to obtain a food reward was increased once the sow had obtained at least five reinforce-
ments at each sequence. The switch and the reward device were only introduced during the learning, training and testing sessions.
Fifteen sows were subjected twice to operant conditioning tests during each 3-week Ž
period: 4.5 and 23 h after the single meal. Seven sows were tested before the meal i.e., .
23 h after the meal of day 14 on day 15, and 4.5 h after the meal on day 16. The eight other sows were tested 4.5 h after the meal on day 15 and 1 h before the meal on day 16.
Animals were tested on a progressive ratio schedule. For the first two sequences, rewards were each obtained after one push. During the following sequences, the number
of times the sows had to push the switch to obtain each successive two rewards was then
Ž increased by five pushes until the end of the 45-min test 1–1–6–6–11–11– . . . –96–
. Ž
96– . . . pushes for an 8-g reward . The food reward was a standard diet 12.2 MJ .
metabolisable energyrkg similar to the one supplied during the week of adaptation to the experimental room, and was the same for all sows.
2.4. Data analysis The number of food rewards obtained during the 45-min testing sessions was
recorded. In addition, data were analysed to determine the average time taken between
two successive pushes on the switch within each sequence, and the duration elapsed between the time when the sow received the reward and started another sequence.
Data were normally distributed and were analysed using the GLM procedure of SAS Ž
. 1990 , according to a Latin square design. Sources of variation in the full model
included the diet and animal. For data with repeated measurements, the effect of the test Ž
. q4.5 and q23 h after the meal was included. Comparison between the 4.5 and 23 h
tests was also analysed.
3. Results
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