www.elsevier.comrlocaterapplanim
Feeding motivation in pregnant sows: effects of
fibrous diets in an operant conditioning procedure
Y. Ramonet
a, J. Bolduc
b, R. Bergeron
b, S. Robert
c,
M.C. Meunier-Salaun
¨
a,)a
INRA, Station de Recherches Porcines, 35590 Saint-Gilles, France
b
UniÕersite La´ Õal, Departement des Sciences Animales, Ville de La´ Õal, Quebec, Canada G1K 7P4
c
Dairy and Swine Research and DeÕelopment Centre, Agriculture and Agri-Food Canada, LennoxÕille,
Quebec, Canada J1M 1Z3
Accepted 20 July 1999
Abstract
The effect of fibrous diets fed to pregnant sows on their feeding motivation was studied by an operant conditioning procedure. Fifteen multiparous pregnant sows were assigned to three dietary treatments, which differed in the nature of the fibrous components, according to a 3=3 Latin square design. Each sow received consecutively during three 3-week periods a concentrate low
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fibre diet, enriched in starch S diet: 2.44 kgrday , and two high-fibre diets, each based on one of
Ž . Ž
these major fibre sources: sugar beet-pulp BP diet: 2.74 kgrday and wheat bran WB diet: 2.90 .
kgrday . All diets provided the same daily metabolisable energy supply of 33.4 MJ. Two 45-min operant conditioning sessions were performed 4.5 and 23 h after the meal on d16 of each 3-week period. Whatever the diet, no differences in the number of rewards received by sows were
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recorded 4.5 and 23 h after the single meal P)0.05 . In addition, there was no effect of time elapsed since food delivery on the feeding motivation of sows. In conclusion, there is no evidence that high-fibre diets reduce feeding motivation as measured by an operant conditioning technique over a medium and a long-term period after a meal. The use of operant tests to measure motivation is considered in the discussion.q2000 Elsevier Science B.V. All rights reserved.
Keywords: Pig; Feeding and nutrition; Feeding motivation; Dietary fibre; Operant conditioning
)Corresponding author. Tel.:q33-02-99-28-50-57; fax:q33-02-99-28-50-80; e-mail: salaun@st-gilles.rennes.inra.fr
0168-1591r00r$ - see front matterq2000 Elsevier Science B.V. All rights reserved.
Ž .
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 ŽLawrence 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
Ž .
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
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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
Ž .
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
Ž .
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
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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 188C"28C. 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 Ž . Ž . 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
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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.
Ž
The level of fibrous components and energy content differed between diets S diet: 21
Ž . Ž .
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
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 Ž1990 , 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 Žq4.5 andq23 h after the meal was included. Comparison between the 4.5 and 23 h. tests was also analysed.
3. Results
The number of rewards earned per test was not affected by the diet, whatever the Ž .
time elapsed since food delivery Table 1 . Between the 4.5 and 23 h tests, differences in the feeding motivation criteria were not significant. At the end of the test, sows had to push the switch on average 46 times to obtain an 8-g reward, which corresponds to 424 pushes cumulated since the beginning of the test. A large variation was found between animals, and the number of rewards obtained by sows was on average 19.3"5.2, ranging from 7 to 32. Within a sequence of increment, the average time taken between
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two successive presses on the switch 3"19 s was not affected by experimental diet ŽP)0.10 . This value corresponded to the rate of working and was similar between. each sequence of increment. Diet only significantly affected the time interval between
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the moment sows received the reward and began another sequence Table 1; P-0.05 , 4.5 h after the distribution of the food. Sows fed the BP diet consumed their reward more rapidly than sows fed the S and WB diets.
A period effect was observed during the test 4.5 h after the meal, sows working more in the last part of gestation. Animals received, on average, six additional rewards in
Ž . Ž .
period 3 week 14; 21.3 rewards , compared to period 1 week 8; 16.7 rewards . During
Ž .
period 2, results were intermediate 19.1 rewards .
Table 1
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Number of rewards received by sows during 45-min operant conditioning tests and time interval s between the reward delivery and the start of another level
Tests Diet Effect
S BP WB MSE Animal Diet Period
Number of sows 15 15 15
Number of rewards per test
UU UU
q4.5 h 19.3 19.5 18.8 3.7 ns
UU
q23 h 20.0 18.5 19.4 4.1 ns ns
Ž .
Time interval s
UUU U U
q4.5 h 63.7a 56.6b 64.5a 32.4
UUU
q23 h 56.8 56.6 59.8 37.2 ns ns
Ž .
4. Discussion
The similar number of rewards obtained by sows in an operant conditioning test 4.5 and 23 h after a single meal showed that the incorporation of sugar beet pulp or wheat bran does not reduce feeding motivation over a medium and a long-term period. Animals received between 2.44 and 2.90 kg of each diet, according to energy require-ments for pregnant sows. This feeding level corresponds approximately to 60% of the ad
Ž .
libitum intake, as recorded by Lawrence et al. 1988 for boars weighing 232 kg. Ž .
Lawrence et al. 1988 demonstrated that a restricted meal which corresponded to 0.6 of ad libitum intake or less and was offered as a single meal to adults pigs had no effect on feeding motivation. Only the feeding motivation of sows restricted to 0.8 of their ad libitum intake decreased 1 h after the meal, but not 5 h after the meal. Using a reward
Ž .
schedule similar to the one used in the present study, Robert et al. 1997 observed that gilts fed a high-fibre diet twice daily had a reduced feeding motivation, compared to animals fed a restricted amount of concentrate diet. However, differences between oat hull, wheat bran and corn cob fibrous diets were limited at 1 h after the morning meal. In addition, as observed in this present study, the effects of the two different fibrous diets on feeding motivation did not differ significantly. In the same way, Ramonet et al. Ž1998 demonstrated an effect of an ad libitum supply of a concentrate diet on feeding. motivation, but did not observe any difference between the effects of the high-fibre diets, either 1 or 5 h after the morning food delivery of 60% of the daily ration. These studies demonstrate the effect of food level on feeding motivation of sows measured by operant conditioning tests, but do not clearly show any effect of the nature of fibre in diets. The limited effect of fibre on the feeding motivation over time was also confirmed in the present study by behavioural recordings around meal time in sows fed experimen-tal diets. The frequency of stereotyped activity was reduced with high fibre diets, more markedly with sugar beet pulp compared to wheat bran diets, and only during the first
Ž .
45-min period following the delivery Ramonet et al., 1999b .
The number of rewards earned by sows in the present experiment was at least twice Ž .
lower than values recorded by Robert et al. 1997 in gilts tested for 60 min. The higher Ž
energy requirements for maternal gain in gilts than in multiparous sows Simmins et al., .
1994 could partly explain the higher feeding motivation of females during the first pregnancy.
The effect of stage of gestation on the number of rewards received by sows was
Ž . Ž
significant 4.5 h after the meal Table 1 . The increase in feeding rate Terlouw et al.,
. Ž .
1991 and the level of stereotypies Bergeron and Gonyou, 1997 observed throughout pregnancy suggest that feeding motivation increases with the stage of pregnancy. However, when sows are fed ad libitum, feed intake decreases as farrowing approaches ŽFriend, 1971; Weldon et al., 1994 . The increase in the number of rewards earned could. also be explained by an increased experience with the operant conditioning device at the end of gestation. Nevertheless, this effect was not significant 23 h after the meal.
The discrepancy between previous results on the effect of fibre on feeding motivation Ž .
might be linked to the composition of the reward. Robert et al. 1997 used their experimental high-fibre diet as food reward, whereas other investigations used a
Ž .
Ž .
preferences have been studied in young pigs Baldwin, 1976 , which will perform
Ž .
operant responses to obtain a palatable solution Kennedy and Baldwin, 1972 . Unpalat-able substances are frequently associated with fibre sources, and result in depressed feed
Ž
intake at very high inclusion levels of crude fibre of 10%–15% of the diet Kennelly and .
Aherne, 1980 . The delivery of a standard diet as the food reward in the present study could have modified the responses of the animals, with sows on the high-fibre treatments working harder to receive more palatable food. Therefore, responses obtained in the operant test could be interpreted as an interaction between the feeding motivation level and the preference level towards the reward. In addition, the consumption of food, when associated with a persistent feeding motivation, facilitates the performance of
Ž .
stereotypies and the activity of animals Terlouw et al., 1993; Haskell et al., 1996 . To assess the level of feeding motivation of growing pigs without involving the ingestion of
Ž .
food during operant tests, Day et al. 1996 used a second-order operant conditioning schedule, in which the animal was trained to work for a feeding-related stimulus. This procedure could avoid the problems of taste preference previously detailed. Day et al. Ž1996 demonstrated that short-term, post-feeding motivation measured with this test. was inversely proportional to the water holding capacity of iso-energetic meals. This methodology could be an alternative way to distinguish between the effects of various high-fibre diets on the food motivation of sows.
Ž . In an experiment conducted with fed-restricted pregnant sows, Hutson 1991 showed that animals are prepared to sustain an energy deficit during operant conditioning tests to
Ž .
gain additional food. Hutson 1991 hypothesised that the energy expended by sows performing operant response is equivalent to that expended while performing stereo-typed behaviour. This author estimated the energetic cost of stereostereo-typed activity at 11 kJrkg live weight0.75 per hour taking into account the data obtained in the study of
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Cronin et al. 1986 . Energy intake during the test corresponded to the energy content of the food reward. Using this methodology in the present experiment, the energy losses of sows could be estimated at 0.45 MJ, whereas animals ingested on average 1.8 MJ EM during the test. This suggests that sows tended to gain more energy during the test than
Ž .
to expend. Hutson 1991 concluded that sows fed at maintenance levels under commer-cial conditions may be constantly very hungry. Our data do not support this hypothesis, but this discrepancy may be due to the occasional exposure of the sows to the food reward device and the short duration of the test in our experiment. But the specific energetic cost of the stereotyped activity need more investigation, with regard to the
Ž .
high energy cost of standing activity in the pig Noblet et al., 1993 .
Previous investigations using operant conditioning tests to measure feeding motiva-Ž
tion in pigs have differed in various ways: the schedule fixed or progressive ratio,
. Ž
second-order schedule or not, measure of extinction , the duration of the test, from 20
. Ž .
Ž .
period following the meal Day et al., 1996; Robert et al., 1997 . The present study confirms that 4 or 5 h after a meal, feeding motivation is high and remains at a high
Ž .
level until the next meal Day et al., 1996; Robert et al., 1997; Ramonet et al., 1998 . More data with operant tests are required to estimate the effect of foodrfibre level on the feeding motivation of sows. Other methodologies used to measure feeding motiva-tion, such as behavioural observations, should also be used, since previous studies have demonstrated an effect of high-fibre diets on the standing, feeding and stereotyped
Ž .
activities of sows Robert et al., 1993; Brouns et al., 1994 .
Acknowledgements
We are grateful to C.H. Malbert for customizing the software, E. Bobillier for the development of the electronic interface and M. Penard who made the reward delivery device. The authors also wish to acknowledge the swine barn staff at Saint-Gilles and particularly M. Massard for animal care. They also wish to thank J.Y. Dourmad, C.H. Malbert and Moira Harris for reading the manuscript.
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