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Effects of two different dietary fermentable carbohydrates on activity and heat production in group-housed growing pigs¹

M. M. J. A. Rijnen^*,,2, M. W. A. Verstegen, M. J. W. Heetkamp^* and J. W. Schrama

^* Adaptation Physiology Group, and Animal Nutrition Group, and and Fish Culture and Fisheries Group, Wageningen Institute of Animal Sciences, Wageningen University and Research Center, Wageningen, The Netherlands

² Correspondence:
Hendrix UTD B.V., P. O. Box 1, S830 MA, Boxmeer, The Netherlands (phone: +31 (0) 485589911; fax: +31 (0) 485574518; E-mail:
martin.rijnen{at}nutreco.com).

	Abstract

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The effects of two sources of dietary fiber (DF) on behavior and heat production (HP) in group-housed growing pigs were studied. Twenty clusters of 14 barrows (50 kg) were fed one of 10 diets. Diets differed mainly in type and content of fermentable DF (fDF) and in content of digestible starch. Five diets contained solvent-extracted coconut meal (SECM) and five diets contained soybean hulls (SBH) as the main fDF source. On an as-fed basis, pigs received 3.5, 13.2, 23.0, 32.7, or 42.4 g•kg^-0.75•d^-1 of SECM or SBH. A total of 280 crossbred growing pigs were used, divided into clusters of 14 pigs each. Pigs were group-housed and fed at 2.5 times the assumed maintenance energy requirements. All clusters were fed similar amounts of NE, ileal-digestible protein and amino acids, vitamins, and minerals. Consequently, DMI differed among diets because NE content decreased with increasing DF content. After a 32-d preliminary period, HP was measured per cluster during a 7-d experimental period in environmentally controlled respiration chambers. Behavior of the pigs was recorded using time-lapse video recordings during two different days within the experimental period. Intake of digestible starch and fDF was different (P < 0.001) among diets, whereas intake of digestible CP was similar among diets. On average, pigs spent 153 min standing, 42 min sitting, 202 min lying on their chest, and 1,043 min lying on their flanks each day. Pigs fed SECM diets spent, on average, less time (P < 0.05) lying on their chest than pigs fed SBH diets. Total time spent on physical activity (i.e., standing plus sitting, 195 min/d) was not affected by diet. Total HP and resting HP were affected by diet and were on average lower (P < 0.01) for pigs fed SECM diets than for pigs fed SBH diets. Activity-related heat production (AHP) averaged 65 kJ•kg^-0.75•d^-1 and was not affected by diet. There was a linear relationship (P < 0.001) between fDF intake and HP, but there was no relationship between fDF intake and AHP. During different parts of the day, fDF intake also affected HP. The saving effect of physical activity on the NE values of fDF from SECM and SBH were 0.56 and 0.84 kJ/g of fDF intake, respectively. Neither of these saving effects was significantly different from zero. We conclude that fDF from SECM and SBH did not affect energy expended on physical activity by growing pigs, and that the NE value of fDF from SECM and SBH was not affected by changes in physical activity.

Key Words: Circadian Rhythm • Diets • Heat Production • Net Energy • Physical Activity • Pigs

	Introduction

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Most (net) energy feed evaluation systems use digestion and utilization data to calculate the potency of a feed ingredient or diet for energy deposition and maintenance. These systems assume that energy requirements for maintenance are unaffected by dietary composition. In growing pigs (e.g., Schrama et al., 1996; 1998) and sows (e.g., Robert et al., 1993; Brouns et al., 1994; Rijnen et al., 2003), however, differences in dietary ingredients affected physical activity. The impact of dietary composition on physical activity indicates that energy requirements for maintenance are not constant. In addition, currently used feed evaluation systems are mostly based on experiments with individually housed growing pigs (e.g., Noblet et al., 1994; CVB, 1998).

Schrama et al. (1998) reported that physical activity of growing pigs was decreased with increasing dietary fiber (DF) content (i.e., DF from sugar beet pulp silage [SBPS]). Rijnen et al. (2003) reported that physical activity of group-housed sows tended to decrease with increasing DF content (i.e., DF from SBPS), an effect that was not constant during the day.

Comparisons between studies suggest that there might be differences in energy utilization of fermentable DF (fDF) from different sources of dietary fermentable carbohydrates (Schrama et al., 1998). These differences in energy utilization of fDF might be related to differences in energy expenditure on physical activity. It can be hypothesized that different sources of DF have different effects on behavior and energy expenditure for physical activity of pigs. In the present study, effects of two sources of DF on behavior and heat production in group-housed growing pigs were studied.

	Materials and Methods

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General
A total of 280 crossbred barrows ([Dutch Landrace x Great Yorkshire] x Pietrain) were used. The experiment consisted of a 32-d preliminary period followed by a 7-d experimental period. Pigs were divided into 20 clusters of 14 pigs each (further divided into two groups of seven pigs each). Cluster was the experimental unit in this experiment. The clusters were randomly assigned to one of the 10 experimental diets. The aim of the present study was to study the effects of fDF intake from two different sources at different levels on behavior and activity-related heat production (AHP) in group-housed growing pigs. Therefore, 10 diets were formulated. Five diets contained different levels of solvent-extracted coconut meal (SECM) (diets 1 to 5) and the other five diets contained different levels of soybean hulls (SBH) (diets 6 to 10). Dietary compositions and analyzed nutrient compositions of the diets are shown in Tables 1 and 2, respectively. For all diets, pigs were fed the same amount of calculated NE, with similar intakes of ileal-digestible protein and amino acids, vitamins, and minerals. The main contrast in the experimental diets was achieved by adding different levels of either SECM or SBH to the diets (Tables 1 and 2). On as fed basis, pigs received 3.5, 13.2, 23.0, 32.7, or 42.4 g•kg^-0.75•d^-1 of either SECM or SBH with their diet. Diets with the lowest DF content (diets 1 and 6) contain DF contents that are normally used in practical diets and can therefore be considered as control diets within diets with the same DF source. Pigs were fed according to the average metabolic BW (kg^0.75) per subgroup. Each subgroup was fed at 2.5 times the assumed maintenance energy requirements. The NE_m was assumed to be 293 kJ•kg^-0.75•d^-1 (Verstegen et al., 1973). Pigs were group-fed twice a day at 0800 and 1530 from two long troughs per cluster. Feed was given as mash feed and the amount of water added to the feed was 2.3 L/kg of DM.

Measurements
Total heat production (HP) was measured at 9-min intervals by determining exchange of oxygen, carbon dioxide, and methane (indirect calorimetry), as described by Verstegen et al. (1987b). These gaseous exchanges were used to calculate HP according the formula of Brouwer (1965). During the last 6 d of the experimental period, HP was measured continuously.

Behavior of the pigs was recorded using time-lapse video recorders during two separate days (i.e., two 24-h periods) within the experimental period. An instantaneous scan-sampling technique (as described by Altmann, 1974) was used to analyze the video recordings for behavioral characteristics (Table 3). The analyses of video recordings for behavioral characteristics were done at 3-min intervals. At these 3-min intervals, the number of pigs that exhibited a specific behavior was recorded. With these data, the percentage of time of all pigs that was spent on a specific behavior was calculated. The average of each performed behavioral characteristic was calculated for the same 9-min intervals as HP (i.e., average of three sampling moments). "Standing" includes standing up, standing, eating, walking, and the act of lying down (Table 3). Therefore, physical activity is defined as standing up, standing, eating, walking, lying down plus sitting. Per group and per day (i.e., 24-h period), the 9-min data on HP were related to physical activity according to the following equation:

[1]

where HP_ij = heat production during day period i and 9-min period j; µ = overall mean; D_i = fixed effect of day period i (i = 1 [from 0700 to 2200] or 2 [from 2200 to 0700]); X_j = physical activity of pigs during 9-min period j; ß = regression coefficient of heat production on physical activity from video recordings in percentage of time of all pigs spent on "standing plus sitting"; and e_ij = error term.

The heat production related to physical activity (AHP, in kJ•kg^-0.75•d^-1) was calculated as follows:

[2]

where AHP_ij = physical activity-related heat production during 9-min period j; X_j = physical activity during 9-min period j of the video recordings; and b = the estimated regression coefficient from HP on physical activity from Eq. [1]. Heat production not related to physical activity or resting heat production (RHP) was derived by subtracting AHP from HP. AHP and RHP were calculated for each 9-min period, including the 1-h periods around feeding, from 0800 to 0900 and from 1530 to 1630.

The energy cost for physical activity (EC_act, in kJ•kg^-0.75•d^-1) was derived from the regression of HP on physical activity, as follows:

[3]

where b = the estimated regression coefficient from HP on physical activity from Eq. [1].

Statistical Analysis
Cluster was the experimental unit. Mean values of HP, AHP, RHP, and the behavioral characteristics were analyzed for effects of diet by ANOVA. The present study focused on the effects of fDF intake from two different sources on HP and AHP during the day. Therefore, HP, AHP, and RHP were analyzed for the effect of diet by linear regression of these traits on the daily intake of fDF (expressed in g•kg^-0.75•d^-1). The LSMEANS procedure was used for treatment comparisons. A contrast method was used to analyze differences between diets with SECM and diets with SBH. All statistics were evaluated with SAS software (SAS Inst. Inc., Cary, NC). The data on HP, AHP and RHP are expressed in kJ•kg^-0.75•d^-1.

	Results

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General
The numbers of clusters and animals used are given in Table 4. One cluster of pigs (diet 5) was removed from the analyses because the lights in the chamber were on during the whole experimental period due to a technical failure. Six pigs were removed during the experiment due to health problems.

For each diet, feeding level was adjusted to the calculated dietary NE content to supply all clusters with similar amounts of NE because NE content decreases with increasing DF content. Consequently, daily DMI was affected by diet (P < 0.001; Table 4). In agreement with the experimental setup, the main difference between the experimental diets consisted of an alteration of the intake of both digestible starch and fDF (P < 0.001; Table 4), whereas the intake of digestible CP was similar for all diets (P > 0.05).

Behavioral Characteristics
On average, pigs spent 153 min standing, 42 min sitting, 202 min lying on their chests, and 1,043 min lying on their flanks each day (Table 5). The average time spent on physical activity (i.e., behavioral characteristics "standing" and "sitting") was 195 min/d. None of the behavioral characteristics was affected by diet (P > 0.10). Contrast analyses showed that pigs that received a diet with SECM spent less time lying on their chests than did pigs that received a diet with SBH (192 and 210 min/d, respectively, P = 0.037). Total time spent on physical activity was not affected by diet (P = 0.966).

Circadian Rhythms.
The average circadian rhythms of HP and AHP of groups of pigs fed different levels of dietary SECM or SBH are illustrated by Figures 1 (HP) and 2 (AHP). Pigs were exposed to 12 h of light (about 300 lx from 0700 to 1900) and 12 h of partial darkness (about 10 lx from 1900 to 0700), and fed twice a day (at 0800 and 1530). HP and AHP were highest during eating and decreased after the meal (i.e., one peak between 0800 and 0900 and one peak between 1530 and 1630). Figure 2 shows that the activity level of pigs is close to zero during the night period (between 2200 and 0700). Figure 2 also shows that AHP decreases very rapidly after the morning meal (0800) to values close to zero, while AHP remains high during the whole afternoon (from about 1200 to 2000).

View larger version (15K): [in this window] [in a new window]   Figure 1. Circadian rhythms in heat production (HP, kJ•kg-0.75•d-1) of group-housed growing pigs, averaged over different levels of dietary solvent-extracted coconut meal () or soybean hulls (•).

View larger version (14K): [in this window] [in a new window]   Figure 2. Circadian rhythm in activity-related heat production (AHP, kJ•kg-0.75•d-1) of group-housed growing pigs, averaged over different levels of dietary solvent-extracted coconut meal () or soybean hulls (•).

	Discussion

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Energy Cost of Activity
In pigs, the energy cost of physical activity can be divided into energy cost of sitting, standing, sitting up, standing up, and walking (Kelly et al., 1978). In the present study, the energy cost of physical activity averaged 479 kJ•kg^-0.75•d^-1 and ranged between 409 and 564 kJ•kg^-0.75•d^-1 for dietary treatments. Some reported values for the energy cost of physical activity of growing pigs are 369, 428, 435 kJ•kg^-0.75•d^-1 (cited by Noblet et al., 1993, from different studies), 269, 401, and 528 kJ•kg^-0.75•d^-1 (Van Milgen et al., 1998). Considering the data from the present study and data from the literature, it seems that the energy cost of physical activity varies widely between growing pigs. Van Milgen et al. (1998) reported effects of BW and breed/castration on the energy cost of physical activity. Van Milgen et al., (1998) suggested that housing conditions and feeding level (i.e., fasted vs. fed animals) might affect the energy cost of physical activity. Furthermore, the technique for measuring or assessing energy cost for physical activity might interact with the energy cost of activity. Furthermore, the energy cost of physical activity depends on the activity pattern of the pigs during the day (i.e., duration of activity, number of changes in position, type of activity, and movements). Because sitting up and standing up cost more energy than sitting and standing, respectively (Kelley et al., 1978), the number of times that a pig stands up or lies down will interact with the energy cost for physical activity. Van Milgen et al. (1998) reported that positional movements as well as metabolic efficiency of movement contribute more to the energetic cost of activity than the act of rising itself. In the present study, pigs were group-housed and able to walk freely in the pen. In most studies that report data on energy cost of physical activity, however, pigs were housed individually (e.g., Hörnicke, 1970; Susenbeth and Menke, 1991; Van Milgen et al., 1998). This difference in housing conditions might be a cause for the high energy cost of physical activity found in the present study (on average 479 kJ•kg^-0.75•d^-1) compared with literature data (on average 407 kJ•kg^-0.75•d^-1; Noblet et al., 1993; van Milgen et al., 1998). This might be related to differences in the number of positional changes and movements. This, however, was not analyzed for in the present study.

In the literature, the energy cost of physical activity in individually housed sows is, on average, e 448 kJ•kg^-0.75•d^-1 or 31.1 kJ/kg^0.75 per 100-min period (averaged for Kelley et al., 1978; Noblet et al., 1993; Ramonet et al., 2000; and Le Goff et al., 2002). In the literature, the energy cost of physical activity in individually housed growing pigs is on average 407 kJ•kg^-0.75•d^-1 or 28.3 kJ/kg^0.75 per 100-min period (averaged for Noblet et al., 1993 and Van Milgen et al., 1998). These literature data suggest that the energy cost of physical activity is about 10% higher for individually housed sows than for individually housed growing pigs. Rijnen et al. (2003) assessed the energy cost of physical activity in group-housed sows (i.e., 446 kJ•kg^-0.75•d^-1 or 31.0 kJ/kg^0.75 per 100-min period) and suggested that the energy cost of physical activity in sows did not depend on housing conditions. In the present study, the energy cost of physical activity was 479 kJ•kg^-0.75•d^-1 for group-housed growing pigs. These data suggest that the energy cost of physical activity is about 7% lower for group-housed sows than for group-housed growing pigs. This might be due to differences in circadian rhythms in physical activity between group-housed sows and group-housed growing pigs (i.e., duration of activity, number of changes in position, type of activity, and movements). In the study from Rijnen et al. (2003), sows were quiet during the whole day except for feeding time and two small peaks in activity during the afternoon, whereas in the present study, pigs were active during the whole afternoon. The difference in energy cost of physical activity between group-housed sows and group-housed growing pigs is in agreement with findings from Van Milgen et al. (1998) that positional movements contribute more to the energetic cost of activity than the act of rising itself.

Literature data described above and data from the present study suggest that there may be an interaction between energy cost of physical activity for sows and growing pigs and housing conditions (individual vs. group housing).

Heat Production and Activity-Related Heat Production
General.
The average AHP (65 kJ•kg^-0.75•d^-1) is lower than the reported average value for AHP of growing pigs by Schrama et al. (89 kJ•kg^-0.75•d^-1; 1998). This difference might be related to differences in activity levels between pigs with different genetics. This difference might also be related to the difference in the techniques used to measure physical activity. In the present study, video recording was used to analyze physical activity, whereas Schrama et al. (1998) used a radar device (Wenk and van Es, 1976). One important difference between these two methods is that in the present study, the video recordings were analyzed for physical activity using 3-min intervals, whereas the radar device measured physical activity continuously (Schrama et al., 1998). Also, video recordings were only from 2 d during the experimental period, whereas the radar device measured activity during the whole experimental period (i.e., 6 d; Schrama et al., 1998).

Circadian Rhythms.
Similar to the results reported by Noblet et al. (1993), Schrama et al. (1996), and Rijnen et al. (2003), HP and AHP were highest during eating and decreased after the meal (i.e., one peak between 0800 and 0900 and one peak between 1530 and 1630; Figure 2) in the present study. The circadian rhythm in AHP from the present study (Figure 2) is very similar to the circadian rhythm in AHP of group-housed growing pigs fed either a high-starch diet or a high-DF diet, as reported by Schrama et al. (1996).

In the present study, fDF intake did not affect energy expenditure on physical activity. There were no differences in AHP between pigs fed diets with SECM and pigs fed diets with SBH. These sources of dietary fermentable carbohydrates mainly contained hemicellulose (SECM) and cellulose (SBH) (CVB, 1998). The differences in composition of the DF fractions (i.e., contents of NDF, ADF, and ADL) of the used SECM and SBH, however, were smaller than expected (Table 2).

The absence of an effect of fDF intake on energy expenditure for physical activity in the present study is in contrast to the observed alteration of physical activity by dietary composition in other studies (e.g., Brouns et al., 1994; Schrama et al., 1998; Rijnen et al., 2003). Both Schrama et al. (1998) and Rijnen et al. (2003) reported that additional intake of fDF from SBPS decreased energy expenditure for physical activity. There is, however, a large difference in composition of the DF fraction used in the present study compared to the experiments of Schrama et al. (1998) and Rijnen et al. (2003). In those studies, pigs were fed different levels of SBPS, which contains high levels of pectin, whereas in the present study, fDF consisted mainly of hemicellulose and cellulose. From a comparison of the studies, it can be hypothesized that the botanical origin and the composition of the fDF fraction is still of importance for an effect on physical activity. This, however, could not be proven in the present study with growing pigs or in the study of Le Goff et al. (2002) with individually housed sows. Besides possible effects on AHP of growing pigs related to differences in composition of the dietary DF, the pattern of VFA production, the velocity of fermentation in the gastrointestinal tract, or specific components in feed ingredients also might be of importance. More research is needed to unravel the mechanisms involved.

Physical Activity and Net Energy
In experiments with growing pigs (Schrama et al., 1998) and sows (Rijnen et al., 2003) an increased intake of fDF from dietary SBPS decreased AHP. This means that the NE value of fDF from SBPS was affected by physical activity. Translated into practical values for the NE value of fDF, this means that reduced activity causes higher NE values. The saving effect of physical activity on the NE value of fDF can be derived from the difference in calculated NE value of fDF during the whole day and during the sleeping period (Rijnen et al., 2003). This saving effect of physical activity on the NE value of fDF can also be derived from the difference in regression coefficient from the regression of fDF on HP during the whole day and during the night period, assuming that the pigs were not active during the night period.

In the present study, regression coefficients for linear regression of fDF on average HP (24h) from SECM and SBH were 1.82 and 4.01 kJ/g of fDF intake, respectively (Table 7). Regression coefficients for linear regression of fDF on HP during the night period from SECM and SBH were 2.38 and 4.85 kJ per g of fDF intake, respectively (Table 7). This means that the saving effect of physical activity on the NE values of fDF from SECM and SBH were 0.56 and 0.84 kJ per gram of fDF intake, respectively (Table 8). Neither of these saving effects of physical activity on the NE values of fDF from SECM and SBH was significantly different from zero. The results from this calculation are similar to the found effects of fDF on AHP during 24 h (neither value was significantly different from zero; Table 7). The effect of physical activity on the NE value of fDF from SECM was not different from that of SBH (P > 0.10). This might be due to the smaller difference in composition of the DF fraction (i.e., contents of NDF, ADF, and ADL) than expected (Table 2).

	Implications

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Many feed evaluation systems for pigs are compiled under the assumption that energy costs for maintenance are constant, including physical activity. In the literature, intake of fermentable carbohydrates is suggested to decrease physical activity in pigs. The present study showed no effects on activity-related heat production for solvent-extracted coconut meal or soybean hulls. Between studies, however, there are differences in effects of fermentable carbohydrates on energy expended on physical activity. Composition of fermentable carbohydrates, along with velocity of fermentation in the hindgut, might be of importance for effects of fermentable carbohydrates on energy expenditure for physical activity. This implies that different fiber-rich feed ingredients might have different net energy values for the fiber fraction of that specific feed ingredient. Further research is needed to investigate the mechanisms involved in differences in net energy values of fiber-rich feed ingredients.

	Footnotes

 
¹ The assistance of S. Hersbach in analyzing the video recordings is gratefully acknowledged.

Received for publication July 27, 2002. Accepted for publication January 13, 2003.

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