The performance and body composition of growing pigs during protein or energy deficiency and subsequent

Seventy-eight 15 kg Polish Landrace gilts were allocated to three feeding regimens (C, E, P). Up to 25 kg the C pigs (control) were fed 95% of ad libitum intake; the group E pigs consumed 40% less energy, while group P animals received 40% less protein compared with group C. From 25 to 70 kg all of the pigs were fed diets differing in energy density (L 12.4 MJ ME; H 13.2 MJ ME) at restricted feeding (R) or ad libitum (A) levels. Animals were slaughtered at 25 kg (n=12) and 70 kg (n=66) and their bodies were analyzed for physical and chemical composition. From 15 to 25 kg the P and E pigs grew slower than controls (367,242 vs 513 g/day). At 25 kg the P pigs had 185 g fat and 142 g protein per kilogram empty body, and entrail weight similar to C pigs. The E pigs had 90 g fat and 163 g protein per kilogram empty body and their entrails were 12% smaller compared with group C and P pigs. From 25 to 70 kg the average daily gain of pigs as well as their physical and chemical body composition at 70 kg did not depend on previous feeding. However, the rate of recovery of particular chemical body components depended on feeding intensity as well as on the previous feeding regimen. It was found that the compensatory response of pigs took about 2-3 weeks and previously underfed pigs are able to fully compensate their anatomical and chemical body composition.


INTRODUCTION
Studies on the compensatory response of the pigs indicate that restricted feeding of pigs decreases their growth rate, however during the following period of growth when a diet adequate for animal requirements is used (realimentation) pigs can increase their growth rate and better utilize feeds (Kyriazakis et al., 1991;Stamataris et al., 1991).
Animals can be restricted in protein or energy intake.Both kinds of restriction change the anatomical and chemical body composition but the scale and quality of these changes depend on many factors, e.g., kind, severity and duration of the restriction feeding (Bikker, 1994;Fandrejewski, 1994;Quiniou et al., 1995).
Data concerning the chemical body composition of pigs during realimentation are scarce, but they suggest that the kind of previous restriction is the most important factor that influences chemical body composition during realimentation (Stamataris, 1991;de Greef, 1992).
In recent studies on compensatory responses, during realimentation pigs were usually fed one kind of diet, while the nutritional value of feed (Fandrejewski, 1994) as well as feeding intensity (Bikker, 1994) can influence the compensatory response.Thus, the results of work done so far cannot be compared directly.We have also not found any study simultaneously comparing the compensatory response of pigs to previous protein or energy underfeeding.
This study was conducted to test the hypothesis that the kind of underfeeding as well as feeding system and kind of diet used during realimentation influence the compensatory response in respect to chemical and anatomical body composition.

Animals and experimental design
The experiment encompassed two periods of pig growth: restriction from 15 to 25 kg and realimentation from 25 to 70 kg.At 15 kg body weight, 78 piglets were randomly divided into three groups (C, E, P -Figure 1) and up to 25 kg the C pigs were fed at a feeding level corresponding to 95% of ad libitum intake while the E group consumed 40% less energy and the P group, 40% less protein compared with group C. The energy intake of the P pigs was comparable to the C pigs.From 25 to 70 kg all pigs were fed diets with a low (L) or high (H) energy content on a restricted feeding level (R, groups LR, HR) or ad libitum (A, groups LA, HA) (Figure 1).The aim of this procedure was to eliminate the influence of voluntary feed intake during realimentation on the compensatory response.Daily rations for the R pigs were changed weekly according to their body weight but feed consumed by pigs fed ad libitum was replenished twice a week.During both restriction and realimentation the pigs were kept in individual pens.

Diets
The composition and nutritional value of the diets are presented in Table 1.From 15 to 25 kg body weight the C and E pigs consumed a basal diet containing 12.9 MJ ME and 167 g CP per kg.The diet for the P pigs (13.1 MJ ME, 130 g CP) was composed by diluting the basal diet with maize starch (2:1).The diets fed to animals during realimentation were based on rapeseed oilmeal (L, 12.4 MJ ME, 166 g CP) or on soyabean meal as the main source of protein (H, 13.2 MJ ME, Central Soya Company 176 g CP).Those diets differed in the lysine:energy ratio resulting from the high lysine supplementation to the L diet to cover the optimal proportion between sulphuric amino acids and lysine.

Slaughter procedure and body analysis
Twelve pigs were slaughtered at 25 kg (four from each group) and 66 at 70 kg.After slaughter the hair was removed from the body, then the entrails including the gastrointestinal tract were emptied and weighed.Carcass, entrails and hair were analyzed for protein, fat, ash and water content (AOAC, 1994).For calculation purposes, the chemical composition and weight of the hair were included in the carcass.

Statistical analysis
Statistical analyses were performed by three-way analysis of variance ANOVA using the Statgraphics version 6.0 Plus software.

Restriction phase (15-25 kg)
The average daily gain of the E and P pigs was reduced (P<0.01)as compared with group C (242, 367 vs 513 g, respectively).The feed conversion ratio was increased by 34.8 % in group P and by 30.0 % in E as compared with group C. At 25 kg, the P and E pigs were older (P<0.01)than the C pigs by 7 and 20 days, respectively (Table 2).
The weight of entrails of the C and P pigs was similar (5.0 and 5.1 kg) and higher (PO.01) compared with the E group (4.4 kg).However, the weight of the gastrointestinal tract of the E pigs was the smallest (PO.01) (1.90 kg) as compared with groups C (2.47 kg) and P (2.39 kg) (Table 2).At 25 kg the protein content in the body of the P pigs was lower (142 g/kg) and the E pigs higher (163 g/kg) as compared with the C pigs (152 g/kg) (Table 2).The kind of restriction influenced (PO.01) the total fat content in the body (129, 185 and 90 g/kg, respectively for the C, P and E pigs).The fat:protein ratio in the body of pigs differed (PO.01) between groups (0.85, 0.55, 1.30, respectively in the C, E, and P pigs).
Experimental treatment did not affect the lean body mass composition of pigs (Table 2) with the exception of the ash:protein ratio.This value differed significantly only between groups E (0.199) and P (0.229).

Realimentation (25-70 kg)
The feed intake of pigs fed ad libitum did not differ significantly between pigs fed the low (L) and the high (H) energy diet (2.39 vs 2.48 kg/day).However, the pigs fed the H diet consumed more (PO.01)energy (30.36 vs 28.16 MJ ME/day) and grew faster (PO.01) (938 vs 846 g/day) but had a similar feed conversion ratio (FCR) (32.6 vs 33.5 MJ ME/kg body gain) compared with the pigs fed the L diet (Table 3).The pigs having free access to feed (A) as compared with those fed according to a restricted feeding system (R) consumed more (PO.01)energy (31.2 vs 27.3 MJ ME/day) and grew faster (PO.01) (961 vs 823 g/day) but their FCR was insignificantly lower (32.7 vs 33.5 MJ ME/kg gain).The energy intake was only slightly higher in both previously underfed groups of pigs (P and E) compared with the C pigs (29.1 and 29.7 vs 29.0 MJ ME/day, respectively) (Table 3).As a consequence, their growth rate did not significantly differ from the C pigs (903 and 899 vs 874 g/day, respectively).
The growth rate from 15 to 70 kg was the lowest in the E (602 g/day) and the highest in the C pigs (709 g/day) while the P pigs grew 709 g/day (Table 3).As a result, at the end of the study both previously underfed groups of pigs were still older, by 5 (group P) and 19 days (group E) compared with the C animals.However, when the age difference at 70 kg is compared with that at 25 kg, it is seen that the P and E pigs made up for time lost during restriction by 2 and 1 days, respectively.
The pigs having free access to feed (A) were at 70 kg younger by 8 days (P<0.01) and their entrails were 0.8 kg heavier (P<0.01)compared with the pigs fed at the restricted level (R) (Table 3).
The total gastrointestinal tract of the group A pigs was heavier (PO.01) (4.99 vs 4.73 kg), as well as the liver (1572 vs 1387 g) and small intestines (1487 vs 1365 g) compared with the R pigs.An interaction (PO.05) of feeding level x kind of diet in liver weight was found.A difference in liver mass between the R and A pigs fed the high energy diet (H) amounted over to 8 % (1271 vs 1387 g) while this difference between R and A pigs fed the low energy diet (L) diet was almost twice as high (15 %; 1501 vs 1765).The gastrointestinal tract of the H pigs was heavier (5.40 vs 4.98 kg) but the liver was over 19 % lighter as compared with the L pigs (1325 vs 1634 g).
In comparison with the pigs that consumed the L diet, the H pigs had less (PO.01) fat (179 vs 191 g/kg) and improved (PO.01) fatprotein ratio (1.15 vs 1.25) but a lower ash:protein ratio (PO.01) (0.178 vs 0.186) in the empty body.
The previous feeding regimen did not influence the body composition of pigs at 70 kg (Table 3).However, the protein content in the body of the E pigs was still slightly higher (158 g/kg) and in the P pigs similar (155 g/kg) compared with the C pigs (156 g/kg).The P pigs were still slightly fatter (193 g/kg) and those from group E, slightly thinner (181 g/kg) compared with the group C pigs (187 g/kg).The fatprotein ratio in the body did not differ between groups.However, its value in the E pigs was still insignificantly improved, whereas in the P pigs, insignificantly worse compared with those in group C (1.15 and 1.25 vs 1.20).An interaction (PO.05) of feeding system x group in fatprotein ratio was detected.A change from restriction to ad libitum feeding did not increase the fatprotein ratio in the C pigs (1.22 vs 1.18) but this value increased considerably in group P (from 1.19 to 1.30) and E pigs (from 1 .05 to 1.16).

DISCUSSION
The results of our study indicate that low energy consumption decreased the rate of daily gain of pigs more than protein restriction.
The feeding system employed from 15 to 25 kg affected the weight of entrails of pigs but only in those that consumed an insufficient amount of energy.The weight of the liver, small and large intestines as metabolically very active organs was reduced the most by decreasing the energy supply and their growth was inhibited before that of muscle tissue, a conclusion also arrived at earlier by Yahya and Millward (1994).In our study, the weight of the liver was only 66%, small intestines 78% and large intestines 79% of the mass of these organs in pigs that consumed a sufficient amount of energy.Data from literature indicate that a lower mass of metabolically active organs decreases the maintenance requirements of animals (e.g., Kong et al., 1985) which could influence their compensatory response during realimentation.
Our results concerning the lower weight of the total gastrointestinal tract of the pigs on a low energy diet are in good agreement with data from literature (e.g., Stamataris et al., 1991;Bikker, 1994).The lack of differences in the weight of the entrails as well as the liver, small and large intestines between control pigs and those consuming lower daily amounts of protein confirmed that growth of this part of the body is rather insensitive to reduction of protein intake if the energy intake is not limited.These results also suggest that the supply of energy is an important factor influencing the growth of internal organs.It was also found that the feeding regimen during restriction strongly influences the chemical body composition of pigs at the end of this phase.A lower protein and higher fat content in the body of pigs consuming low amounts of protein was caused by an excess of energy over requirements as well as the possibility for accruing protein.Inversely, too low an energy supply increases the activity of lipolytic enzymes, especially in the backfat to cover the energy requirements of animals (Whang et al., 2000) and as a consequence the fat content in the body declines.On the other hand, during energy deficiency the body protects amino acids against using them as an energy source (Simmon, 1989) and does not decrease the protein content in the body.
The results of our study indicate that during realimentation, the growth rate of pigs previously consuming a low amount of protein as well as those fed a low amount of energy did not differ significantly compared with controls.Thus, if compensatory growth is considered as a higher growth rate of previously underfed animals, these pigs did not show any compensatory growth.A consequence of this was the older age of both previously underfed groups at the end of the study.That fact indicates that the possibility of fully recovering weight-for-age is rather unlikely.However, if the growth of pigs during the following weeks of realimentation is considered it was clear that both previously underfed groups of pigs showed compensatory growth, except those fed ad libitum on high energy diet (Figures 2  and 3).The longer realimentation lasted, the smaller the difference between both previously underfed groups of animals was found.These findings confirm a theory (Ryan, 1989) that compensatory growth occurs for only a very limited time Week of the study following realimentation, and its occurrence may be highly unpredictable, given the many factors that can influence the growth of an animal.Studies on ruminants (Ryan, 1989) indicate that the higher growth rate of sheep previously underfed for energy could result from filling of their alimentary tract.We did not find any reports concerning this phenomenon in pigs, but in our study pigs previously fed at a low energy level showed compensatory growth at both restricted and ad libitum feeding (Figures 2 and 3).This could mean that ad libitum feeding during realimentation does not determine the compensatory response.It also seems that the lower mass of metabolically active organs (such as the liver, small and large intestines) of the pigs on an energy-restricted diet caused lower maintenance requirements of these pigs (Koong et al., 1985) and during following realimentation more energy from the diet could probably be allocated to covering growth requirements.
In the case of pigs previously consuming inadequate amounts of protein, an increased a fat content in their body could play an important role (de Greef et al., 1992).
The final protein and fat content in the body did not differ between groups.From this point of view, previously underfed animals recovered their chemical body composition, a result which has been shown in only a very few studies (e.g., Sarkar, 1983;Fandrejewski, 1994).
The results of our study indicate that the feeding level (independent of the kind of diet) and kind of previous underfeeding as well as recovering components of the body influence the rate of recovery.At a restricted feeding level, pigs previously fed a low protein diet were able to recover their protein content in the body before they reached the target weight because at 70 kg their body contained more protein than the control animals (Figure 4).This was due to the large fat stores deposited in their body during restriction that in the subsequent realimentation could be mobilized as an extra source of energy for protein deposition, which was already indicated in an earlier study (e.g., Close et al., 1978).At this feeding level, the fat content in the body of our pigs resembled that of control pigs.However, at ad libitum feeding the amount of energy that animals could use (consumed with feed Figure 4.A protein content in the body of pigs at 70 kg body weight in respect to feeding system and kind of diet: a) diet L -restricted feeding; b) diet H -restricted feeding; c) diet L-ad libitum; d) diet H -ad libitum and restored in the body) was too high as compared with their protein accretion ability and ultimately they were fatter and contained less protein in the body as compared with control pigs.
The pigs previously having a low daily energy intake and fed at a restricted level during realimentation still had a higher amount of protein in the body at target weight because their energy intake was too low to fully recover their body fat content (Figure 5).Ad libitum feeding of this group of pigs increased the intake of energy and as a consequence its distribution between protein and fat deposited in the body must be changed.Pigs fed in this way favoured fat to protein accretion in the body, which allowed them to decrease the protein content in the body to the level of control pigs and even to restore fat content before reaching 70 kg (Figure 5).
Data from literature concerning compensatory growth regarding the time taken to compensate chemical body composition of pigs are unclear.Sarkar et al. (1983) reported full recovery of chemical body composition up to 90 kg in pigs previously consuming daily low energy.On the other hand, Stamataris et al. (1991) did not obtain a compensation of chemical body components at 24 kg in pigs previously underfed from 6 to 12 kg.Data presented by Bikker (1994) also show that pigs underfed from 25 to 45 kg at the end of realimentation (80 kg) had still less fat and more protein and water in the body than normally fed animals.
In pigs previously fed a low protein diet (Fandrejewski, 1994) full compensation of chemical body composition was found at 60 kg.In contrast, de Greef et al. (1992) did not find recovery of chemical body components in pigs weighing 90 kg and previously underfed from 28 to 65 kg.A discrepancy of the results of cited studies is caused by different severity and duration of the restriction as well as duration of the realimentation period.Additionally, the animals differed in age and were underfed in a dissimilar way so the results of these works cannot be directly compared.
It should be pointed out that in our study, the body of pigs fed a diet with a high energy content (H) contained less fat and had a better fatprotein ratio in spite of their higher feeding intensity.This resulted from the improved lysine:ME ratio in this diet and from the response of the pigs indicating that young animals having a large growth capacity are much more sensitive to energy than protein (lysine) supply (Lawrence et al., 1994).
Considering the influence of feeding level on the fatprotein ratio in the body of pigs from particular groups, it could be pointed out that a change in restricted to ad libitum feeding did not increase the fatprotein ratio in the C pigs, but this value was considerably higher in the previously protein-(P) and energy-(E) restricted pigs.Such a response of pigs is probably caused by differences in the proportion of fat and protein deposited in the daily body gain of pigs previously underfed in both energy and protein terms.This fact should be taken into consideration in practice in the nutrition of pigs on which some nutritional restriction was previously imposed.
The greater mass of the gastrointestinal tract of pigs fed the diet with the lower energy content (L) resulted from the heavier weight of their liver.The main reason for the heavier liver mass of these pigs was probably the glucosinolate content in the L diet where rapeseed meal was the main source of protein (Thomke et al., 1998).
It was found that that the final weight of entrails and of some organs (the liver, small and large intestines) did not differ significantly between groups C, E and P. The lack of differences, especially in the E pigs, which had the lowest weight of entrails and intestines at 25 kg, indicated that this part of the body of these animals grew much faster as compared with the remaining groups.It also means that these pigs showed compensatory growth of their viscera.This phenomenon was also reported by Koong et al. (1985), Stamataris et al. (1991), Bikker (1994) in pigs previously underfed for energy, and by Ryan (1989) in a study on cattle.

CONCLUSIONS
Based on the results of this study it may be concluded that the growth rate of pigs is much more sensitive to energy than protein restriction in the diet.The kind of underfeeding influences the fat content in the body and pigs consuming inadequate amounts of energy have decreased, while those consuming inadequate amounts of protein have increased fat stores.
The growth of internal organs is much more sensitive to energy than protein restriction and the organs whose growth is most inhibited are the liver and small intestines.

Figure 1 .
Figure 1.Design of the study

TABLE 2
The performance of pigs from 15 to 25 kg and body composition of the pigs at 25 kg ABC pO.01 abc PO.05 1 stomach + small intestines + large intestines + liver + pancreas + spleen

TABLE 3
Performance of pigs during realimentation and the body physical and chemical composition * PO.01, * P<0.05; ns -difference nonsignificant; experimental factors: A-feeding system; B-diet; C-group