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J. Anim. Sci. 2003. 81:2783-2791
© 2003 American Society of Animal Science

Effect of dietary protein fluctuations and space allocation on performance and carcass quality of growing-finishing pigs1

M. S. Edmonds*,2 and D. H. Baker{dagger}

* Nutrition and Product Development, Kent Feeds, Inc., Muscatine, IA 52761 and and {dagger} Department of Animal Sciences, University of Illinois, Urbana 61801


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Two trials with growing-finishing pigs were conducted to evaluate the effects of fluctuating dietary CP levels and/or space allocation on performance and carcass traits. In Trial 1, three CP regimens were used with 216 growing-finishing pigs (mixed sex). Average initial and final weights of pigs were 31 and 103 kg, respectively. The CP regimens consisted of: 1) control (18% CP from wk 0 to 4; 15% CP from wk 4 to 12); 2) moderate CP variations (MCPV = 19.5% CP from wk 0 to 2, 16.5% CP from wk 2 to 6, 13.5% CP from wk 6 to 8, 16.5% CP from wk 8 to 10, 13.5% CP from wk 10 to 12); and 3) extreme CP variations (ECPV = 21% CP from wk 0 to 2, 15% CP from wk 2 to 4, 18% CP from wk 4 to 6, 12% CP from wk 6 to 8, 18% CP from wk 8 to 10, 12% CP from wk 10 to 12). Overall (wk 0 to 12), treatment differences were not observed (P > 0.05) for gain, feed intake, CP intake, gain:feed ratio, or gain/CP intake. Trial 2 involved 360 finishing pigs (mixed sex) in a 3 x 2 factorial arrangement (three dietary CP regimens, two floor space allowances). The diets consisted of: 1) control (16% CP from wk 0 to 4, 15% CP from wk 4 to 8; 14% CP from wk 8 to 12); 2) MCPV (17.5% CP from wk 0 to 2, 14.5% CP from wk 2 to 4, 16.5% CP from wk 4 to 6, 13.5% CP from wk 6 to 8, 15.5% CP from wk 8 to 10, 12.5% CP from wk 10 to 12); and 3) ECPV (19% CP from wk 0 to 2, 13% CP from wk 2 to 4, 18% CP from wk 4 to 6, 12% CP from wk 6 to 8, 17% CP from wk 8 to 10 wk, 11% CP from wk 10 to 12). Pigs were provided with either 1.12 m2 (uncrowded; five pigs/pen) or 0.56 m2 (crowded; 10 pigs/pen). Average initial weight was 49 kg and final weights were 126 kg (uncrowded) and 118 kg (crowded). Overall (0 to 12 wk), crowded pigs had lower (P < 0.05) ADG (822 vs. 916 g) and feed (as-fed) intakes (2,633 vs. 2,876 g) than uncrowded pigs. At the end of the 12-wk trial, a control vs. ECPV x space interaction (P < 0.05) occurred for weight gain, fat depth, and percentage of lean. Thus, uncrowded pigs fed ECPV gained faster (933 vs. 887 g) but had a lower percentage of lean (53.5 vs. 54.5) than controls, whereas crowded pigs on the ECPV regimen gained more slowly (812 vs. 842 g) but were leaner (54.8 vs. 54.6%) than those on the control CP regimen. Despite the wide dietary CP fluctuations, pigs in both trials consumed about the same quantity of CP during the 12-wk feeding periods. These data suggest that uncrowded pigs respond differently than crowded pigs to fluctuating levels of dietary CP.

Key Words: Compensatory Growth • Crowding • Dietary Protein • Pigs


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Developing new feeding strategies to improve the efficiency of lean meat production is vital to the growth of the pork industry. One such strategy is induced compensatory growth, an area that has been evaluated in growing-finishing pigs by a number of researchers over many years.

Several studies (Robinson, 1964Go; Pond and Mersmann, 1990Go; Critser et al., 1995Go) have investigated the effect of restricted feed intake followed by ad libitum feeding in growing pigs. In work by Wahlstrom and Libal (1983)Go, however, CP levels were varied without feed being restricted. Their work revealed that grower pigs fed low-CP (12%) diets responded more in the subsequent growth periods to 14% CP diets than those previously fed the 16% CP diet. Further work by de Greef et al. (1992)Go indicated that grower pigs (28 to 65 kg) that had been fed diets severely deficient in protein (roughly 9% CP) had partial compensatory growth responses in the finishing stage (65 to 105 kg) compared with those that had been fed an excess CP level (20.5%) in the grower stage. Two studies by Chiba et al. (1994Go; 1995)Go also showed compensatory growth responses in finishing pigs previously fed marginal AA levels during the grower stage, whereas a third study did not (Chiba et al., 1999Go).

To our knowledge, there are no published reports in which lean (percentage of lean >= 54%) genetic lines of growing-finishing pigs have been fed periods of excess dietary CP followed by identical periods of reduced dietary CP to determine their effect on compensatory growth. In addition, we are not aware of any studies in which pigs have been crowded to determine the effect of this environmental stressor on compensatory growth responses. Therefore, the objectives of our trials were to evaluate the effect of protein fluctuations in growing-finishing pigs on performance and carcass characteristics and to determine if dietary protein fluctuations and compensatory growth responses are affected by crowding.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Implications
 Literature Cited
 
General Procedures
Two trials were conducted with growing-finishing pigs. In Trial 1, the pigs were housed in an open-front grower-finisher building with 65% slatted and 35% solid concrete floors. The pigs in Trial 2 were housed in a naturally ventilated grower-finisher building with fully slatted floors. Pigs were randomly allotted to treatments from blocks based on ancestry, weight, and sex in randomized complete-block designs. One self-feeder (five and three feeder holes for Trials 1 and 2, respectively) and one nipple waterer were provided in each pen. Environmental temperature in the buildings ranged from 15 to 22°C during the trials. The experimental control diets (Regimen 1) for both trials were formulated to meet or exceed all nutrient requirement estimates (including CP and lysine) of 20- to 120-kg pigs (NRC, 1998Go). Diets were fed in meal form.

Animals.
Crossbred pigs resulting from the cross of PIC (Franklin, KY) Line 356 males and Camborough 22 females were used for both trials. All research protocols followed the guidelines stated in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching.

Protocol and Design for Trial 1.
Two hundred sixteen growing-finishing pigs were used in a trial involving three CP regimens. There were six replications (pens) per treatment. Each pen contained six gilts and six barrows, and the pigs used in this 12-wk trial averaged 31 kg at trial initiation. Pen dimensions were 5.6 m (length) x 2.0 m (width). With 12 pigs in each pen, the space allocation per pig was 0.93 m2. The trial was initiated on November 10, 1999, and ended on March 15, 2000.

The CP regimens and experimental diets are shown in Table 1Go. The control (Regimen 1) consisted of feeding 18 and 15% CP diets during wk 0 to 4 and 4 to 12, respectively. Regimen 2 involved moderate changes in CP levels (± 1.5 units compared to Regimen 1): 19.5, 16.5, 16.5, 13.5, 16.5, and 13.5% CP for wk 0 to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 10 and 10 to 12, respectively. The extreme variations (± 3 units compared with Regimen 1) in CP (Regimen 3) were 21, 15, 18, 12, 18 and 12% CP for wk 0 to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 10, and 10 to 12, respectively. Pigs were weighed after 4, 8, and 12 wk on test, with feeders weighed at either 2- or 4-wk intervals, depending on whether diets were changed. All diets were formulated using a standard level of a commercial premix, which consisted of meat and bone meal, corn distillers dried grains with solubles, wheat middlings as protein sources, and vitamins, trace minerals, salt, dicalcium phosphate, calcium carbonate, lysine, and medication. The remainder of the diets contained corn and soybean meal, which were varied to accomplish target levels of CP. All diets were medicated with 33 mg/kg of bacitracin methylene disalicylate (Alpharma, Inc., Ft. Lee, NJ), and the average particle size of the mixed diets was 764 µm.


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  		Table 1. Composition of experimental diets (as-fed basis) for Trial 1
 
The CP regimens in Trial 1 were designed to provide (on average) NRC (1998)Go required levels of CP and lysine during each 4-wk period, assuming feed intake would be similar within 2-wk periods and across the three regimens. Thus, the average CP concentration within succeeding 4-wk growth periods was 18 (wk 1 to 4), 15 (wk 4 to 8), and 15% (wk 8 to 12); although with the exception of Regimen 1, the (average) CP levels were achieved by feeding excess CP for the first 2 wk followed by deficient CP for the next 2 wk of each 4-wk period. Admittedly, however, the last 4 wk of the trial during which pigs were in the weight range of 80 to 103 kg, Regimens 1 and 2 provided (average) CP and lysine levels above NRC (1998)Go recommendations during both 2-wk periods of the last 4 wk of the trial.

Protocol and Design for Trial 2.
Three hundred sixty finishing pigs (mixed sex) were used in a 3 x 2 factorial arrangement of treatments involving three CP regimens and two levels of space. Pigs and feeders were weighed every 2 wk. There were eight replications (pens) per treatment. Each pen contained either two gilts and three barrows or three gilts and two barrows (uncrowded) or four gilts and six barrows or six gilts and four barrows (crowded) so that the sex ratio was constant across the blocks. The average initial weight was 49 kg. Pen dimensions were 2.44 m (length) x 2.44 m (width). After adjusting for the size of the feeder (0.37 m2), pigs in the uncrowded pens had 1.12 m2 per pig, whereas those in the crowded pens had 0.56 m2 per pig. Each feeder had two feeder spaces. This trial was started on July 20, 2000, and ended on December 19, 2000.

Listed in Tables 2 Goand 3Go are the CP regimens and experimental diets used in Trial 2. Regimen 1 (Control) consisted of feeding 16, 15, and 14% CP diets during wk 0 to 4, 4 to 8, and 8 to 12, respectively. The moderate changes (± 1.5 units compared to Regimen 1) in CP levels (Regimen 2) involved 17.5, 14.5, 16.5, 13.5, 15.5, and 12.5% CP for wk 0 to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 10, and 10 to 12, respectively. Regimen 3 had extreme variations in CP levels (± 3 units compared with Regimen 1): 19, 13, 18, 12, 17, and 11% CP for wk 0 to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 10, and 10 to 12, respectively. The commercial premix used in all these diets was similar to that used in Trial 1, with the exception that it also contained supplemental phytase (BASF Corp., Mount Olive, NJ). As in Trial 1, higher and lower levels of CP were obtained by adding or reducing soybean meal at the expense of corn. Bacitracin methylene disalicylate was incorporated into all diets at 33 mg/kg, and the average particle size of diets was 755 µm.


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  		Table 2. Composition of experimental diets (as-fed basis) during weeks 0 to 6 of Trial 2
 

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  		Table 3. Composition of experimental diets (as-fed basis) during weeks 6 to 12 of Trial 2
 
The CP regimens in Trial 2 were designed to provide (on average) NRC (1998)Go required levels of CP and lysine during each 4-wk period, assuming feed intake would be similar within 2-wk periods and across the three regimens. Thus, the average CP concentration within succeeding 4-wk growth periods was 16 (wk 0 to 4), 15 (wk 4 to 8), and 14% (wk 8 to 12); although with the exception of Regimen 1, the (average) CP levels were achieved by feeding excess CP for the first 2 wk followed by deficient CP for the next 2 wk of each 4-wk period. Admittedly, however, the last 4 wk of the trial during which pigs were in the weight range of 80 to 127 kg, Regimen 1 provided (average) CP and lysine levels above NRC (1998)Go recommendations.

Diet Analysis.
Calcium and phosphorus values were measured by flow-infection analysis (Hambleton, 1977Go). Salt was determined as soluble chloride (Cotlove, 1963Go). Crude protein analysis was determined by the combustion method (percentage N x 6.25; AOAC, 1996Go). For calculation of CP intake and weight gain/CP intake, analyzed CP values were used in all cases.

Carcass Analysis.
In Trial 2, all pigs were slaughtered at the end of the 12-wk test period. Fat and loin depth were measured using an animal ultrasound system at Iowa Beef Processors, Inc. (Columbus Junction, IA) with percentage of lean also reported for each pig. Dressing percentage was calculated by dividing hot carcass weight (head removed) by live BW multiplied by 100.

Statistical Analysis.
Each pen of pigs was the experimental unit for all statistical analyses. All data were subjected to analysis of variance using the GLM procedures of SAS (SAS Inst., Inc., Cary, NC). Preplanned nonorthogonal single-df comparisons were made with an alpha level of P < 0.05 used to establish treatment differences and interactions.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Implications
 Literature Cited
 
Trial 1: Late Grower Stage (0 to 4 wk) and Early Finisher Stage (4 to 8 wk).
During the 0- to 4-wk period (i.e., between 31 and 55 kg of BW), there were no significant performance differences among the three dietary regimens (Table 4Go). In contrast, during wk 4 to 8, gain was reduced (P < 0.05) by 4.9% when pigs were fed Regimen 3 (18%/12% CP) vs. Regimen 1 (15% CP). Gain:feed ratio tended (P = 0.07) to be reduced by 5.5% for pigs on Regimen 3 vs. Regimen 1 during the 4- to 8-wk period.


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  		Table 4. Effect of crude protein regimens on performance of growing-finishing pigs (Trial 1)a
 
Late Finisher Stage (8 to 12 wk) and Overall (0 to 12 wk).
During wk 8 to 12 (i.e., between 80 and 103 kg of BW), gain, gain:feed ratio, and gain/CP intake were improved (P < 0.05) by 8.7, 6.2, and 10.3%, respectively, for pigs on Regimen 3 (18%/12% CP compared to those on Regimen 1 (15% CP). Moreover, gain and gain/CP intake were also improved (P < 0.05) by 5.5 and 5.4%, respectively, for pigs on Regimen 2 (16.5%/13.5% CP) relative to those on Regimen 1. Overall (0 to 12 wk), pigs on all three regimens performed similarly.

Trial 2: Early Finisher Stage (0 to 2 and 2 to 4 wk).
Data in Table 5Go show that during wk 0 to 2, pigs on Regimen 3 (19% CP) had a 4.4% improvement (P < 0.05) in gain:feed ratio, but a 9.8% decrease (P < 0.05) in gain/CP intake compared with those on Regimen 1 (16% CP). Gain/CP intake was also decreased (P < 0.05) by 7.4% for pigs on Regimen 2 (17.5% CP) relative to those on Regimen 1.


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  		Table 5. Effect of crude protein regimen on performance and carcass traits in uncrowded and crowded finishing pigs (Trial 2)a
 
Gain, feed intake, and protein intake were reduced (P < 0.05) in pigs crowded during wk 2 to 4 compared with those not crowded. During wk 2 to 4, pigs on Regimen 3 (13% CP) exhibited decreased gain (5.9%) and gain:feed ratio (10.1%) compared with those on Regimen 1 (16% CP). In contrast, gain/CP intake was increased by 13.2% for those on Regimen 3 vs. 1. Pigs on Regimen 2 (14.5% CP) consumed less (P < 0.05) protein but had higher (P < 0.05) gain/CP intake values than those on Regimen 1 during wk 2 to 4.

Middle Finisher Stage (4 to 6, 6 to 8 wk).
A crowding effect occurred during these periods. Thus, feed intake was reduced (P < 0.05) in crowded vs. uncrowded pigs during wk 4 to 6 and 6 to 8. Gain and gain:feed were improved (P < 0.05) by 14.7 and 10.6%, respectively, whereas gain/CP intake was decreased by 9.9% (P < 0.05) for pigs on Regimen 3 (18% CP) compared with those on Regimen 1 (15% CP) during wk 4 to 6.

During wk 6 to 8, crowded pigs had lower (P < 0.05) gain, feed intake, and CP intake than uncrowded pigs. Pigs on Regimen 3 (12% CP) had an 8.8% decrease (P < 0.05) in gain:feed, but a 13.3% increase (P < 0.05) in gain/CP intake compared with those on Regimen 1 (15% CP) during wk 6 to 8. A Regimen 1 vs. 3 x crowding interaction (P < 0.05) occurred (wk 6 to 8) for gain:feed ratio (P < 0.05), in which uncrowded pigs were unaffected by either regimen, whereas feed efficiency of crowded pigs was reduced by 16.9% on Regimen 3 vs. 1.

Late Finisher Stage (8 to 10, 10 to 12 wk).
Gain, feed intake, and protein intake were reduced (P < 0.05) when pigs were crowded during both wk 8 to 10 and 10 to 12. Gain/CP intake was reduced (P < 0.05) by 11.4% for pigs on Regimen 3 (17% CP) compared with those on Regimen 1 (14% CP) during wk 8 to 10. In contrast, gain/CP intake was increased (P < 0.05) by 13.7% for pigs on Regimen 3 compared to those on Regimen 1 during wk 10 to 12. Also, during wk 10 to 12 gain:feed was poorer (P < 0.05) in pigs on Regimen 3 vs. those on Regimen 1.

Overall (0 to 12 wk).
Final body weight, gain, feed intake, and CP intake were reduced (P < 0.05) for pigs crowded compared to those not crowded. There were six (final weight, daily gain, gain:feed ratio, gain/CP intake, fat depth, and percentage lean) Regimen 1 vs. 3 x crowding interactions (P < 0.05) in the overall 12-wk period. The Regimen 1 vs. 3 x crowding interaction for gain, gain:feed ratio, and gain/CP intake suggested that the responses to widely fluctuating CP levels were positive in uncrowded pigs, whereas they were negative in crowded pigs. The reverse was true, however, for carcass fat depth in that the extreme dietary CP fluctuations resulted in increased fat depth in uncrowded pigs but in decreased fat depth in crowded pigs.

A Regimen 1 vs. 2 x crowding interaction (P < 0.05) occurred for final weight and daily gain. An increase in gain of 4.5% occurred with uncrowded pigs, whereas a 3.2% decrease in gain resulted for crowded pigs on Regimen 2 compared with those on Regimen 1.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Implications
 Literature Cited
 
Among the findings in this work was that 2 wk periods of overfeeding CP followed by 2-wk periods of underfeeding CP during 12 wk of feeding did not reduce weight gain, feed efficiency, or gain per unit of CP intake. In fact, protein utilization (i.e., gain/CP intake) was actually improved in uncrowded finishing pigs that were subjected to extreme up-and-down changes in dietary CP. The extremes imposed in Regimen 3 herein also resulted in nearly the same total 12-wk CP intakes as those occurring on the control regimen. In Trial 2, where pigs and feeders were weighed every 2 wk, it was possible to evaluate gain/CP intake for each of the six growth periods. This revealed, without exception, that the utilization of protein was lower when excess vs. inadequate CP was fed. Moreover, these differences occurred regardless of whether pigs were crowded or uncrowded.

Under conditions of crowding, growth performance, but not carcass merit, was decreased by both the moderate and the extreme up-and-down fluctuations in dietary CP. Also, uncrowded pigs, given the extreme regimen, had more backfat than control pigs, even though they gained faster and had gain:feed ratio and gain/CP intake values that were equal to or better than pigs on the control regimen.

One might have thought, particularly with Regimen 3, that the three periods of overfeeding CP would result in wasteful use of the CP intake. As indicated by the reduced gain/CP intake during these periods, this seemed to be the case. However, when these excess-CP feeding periods were followed by inadequate-CP feeding periods, compensatory CP utilization seemed to occur such that at the end of the 12-wk feeding periods, CP utilization was not decreased, and in fact was actually increased in Trial 2.

During the last 4 wk of the 12-wk test period in Trial 1, fluctuating CP levels resulted in substantial improvements in gain, feed efficiency, and gain/CP intake compared with those occurring in pigs on the control regimen. In Trial 2, we observed that uncrowded pigs gained faster when fed diets fluctuating in CP compared with those fed the control diets, but in contrast, crowded pigs gained slower when fed the up-and-down CP regimens. Work by van Milgen and Noblet (2001)Go in individual pigs showed that partial compensatory growth occurs in 40- to 80-kg pigs by altering the feed allowance (restricted fed for 6 d followed by ad libitum feeding for 12 d with this pattern of feeding repeated three times) vs. feeding pigs ad libitum the entire time.

Research by Wahlstrom and Libal (1983)Go indicated that grower pigs previously fed 12 vs. 16% CP for 4 wk had partial compensatory growth when fed 14% CP diets to 52 kg of BW. Further work by de Greef et al. (1992)Go showed that when grower pigs (28 to 65 kg) had been fed diets severely deficient in CP (9% CP), partial compensatory growth occurred in the finishing stage (65 to 105 kg) compared with those pigs fed much more CP (20.5%) in the grower stage. No compensatory growth occurred (Chiba et al., 1999Go) in finishing pigs previously fed grower diets that were marginally deficient in amino acids, but in three other similar studies (Chiba et al., 1994Go; 1995Go; Fabian et al., 2002Go) compensatory growth responses did occur. In grower-finisher studies involving moderate feed restriction followed by ad libitum feeding, Bikker et al. (1996a)Go and Robinson (1964)Go observed that growth performance was either reduced or similar to that of pigs not restricted. Other trials by Campbell et al. (1983)Go and Prince et al. (1983)Go showed that performance was equal to that of unrestricted pigs (or improved) when pigs were initially restricted fed and then ad libitum fed. In the above studies involving changes in CP levels and/or feed allowances, the pigs were individually fed in seven of the 10 studies, but crowding was not evaluated in any of these trials.

In research where CP levels (10, 17, 24, 31%) were varied in only the starter stage (5 to 24 kg), Wyllie et al. (1969)Go found that, overall (5 to 92 kg), pigs fed increased CP up to 24% in the starter period had poorer feed efficiencies but improved gains with no change in carcass composition. Zimmerman and Khajarern (1973)Go observed no differences in overall (5 to 90 kg) performance and body composition from feeding starter pigs (5 to 23 kg) diets that were low (10%) or high (24%) in CP, although growth was reduced by 16% from feeding the 10 compared to the 24% CP diets in the starter period. In addition, Hogberg and Zimmerman (1978)Go found that pigs of a fat strain were able to compensate in the grower-finisher stage from being fed 10% CP (vs. 20% CP) in the starter period, but in contrast, a leaner strain was not able to compensate. In this study, they also observed a smaller longissimus muscle in the lean strain that was initially fed the very low CP (10%) diet, but this did not occur in the fat strain. Furthermore, Mrõz et al. (1987)Go observed that young pigs (21 to 84 d of age) grew more slowly when fed diets lower in lysine, but they subsequently grew faster in the finisher stage, thus resulting in similar overall (21 to 225 d) performance and carcass traits.

We observed in Trial 2 a regimen x space interaction, in that when uncrowded pigs were exposed to extreme CP variations, backfat increased, and percentage of lean decreased compared with essentially no change in these measurements in crowded pigs. In contrast to these carcass measurements, we found that gain:feed ratio and gain/CP intake were similar in uncrowded pigs fed extreme CP variations compared with those on the control diets. Other researchers (Wahlstrom and Libal, 1983Go; Chiba et al., 1999Go; Fabian et al., 2002Go) observed no change in carcass quality in finishing pigs (100 to 108 kg) that previously were subjected to marginal AA deficiencies in the grower stage. In addition, Campbell et al. (1983)Go and Prince et al. (1983)Go observed that moderate feed restriction in grower pigs resulted in similar carcass composition in the finishing (90 to 100 kg) stage. Moreover, Wyllie et al. (1969)Go and Zimmerman and Khajarern (1973)Go found no changes in carcass composition of finishing pigs that were previously fed low CP diets in the starter stage compared to those fed higher CP levels in the starter stage. Hogberg and Zimmerman (1978)Go also observed similar carcass quality in fat-strain, but not lean-strain finishing pigs previously fed low-CP starter diets compared with higher CP starter diets.

Considerable research has been conducted in an attempt to understand the mechanisms behind compensatory growth in pigs. Some have shown a marked increase in organ weights following a period of feed restriction (Pond and Mersmann, 1990Go; Stamatarist et al., 1991Go; Bikker et al., 1996bGo). Other work by Campbell et al. (1983)Go suggested that dietary restriction in one phase might result in a decrease in the energy requirement needed for maintenance in subsequent stages of growth. Research by Atinmo et al. (1978)Go showed that in rehabilitated pigs (fed 6% CP diets for 8 wk after weaning followed by adequate diets to 20 wk of age), plasma growth hormone concentrations increased, whereas insulin levels decreased compared with pigs fed control diets.

Could our response in growth rate from fluctuating CP levels be due to increased growth hormone concentrations and/or an increase in insulin levels (i.e., since both hormones are involved in the regulation of protein synthesis)? It would be interesting to measure these hormones in uncrowded and crowded pigs to determine if an explanation could be given as to why crowded pigs respond differently than uncrowded pigs to fluctuating levels of CP. Moreover, studies may also be needed to evaluate the time period required for fluctuating CP levels and what effect this might have on compensatory growth responses. Perhaps had we used high rather than low CP during the last 2 wk of Trial 2, the uncrowded pigs on the extreme CP fluctuations would not have had the increased fat depth that was observed in this trial.


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
Literature Cited
 
Feeding fluctuating levels of dietary crude protein to uncrowded, but not crowded, growing-finishing pigs resulted in significant compensatory growth responses compared with pigs fed constant levels of protein. Repetitive 2-wk regimens of protein overfeeding followed by underfeeding over a 12-wk period did not decrease gain per unit of crude protein intake. The potential for pigs raised outdoors in uncrowded environments to benefit from fluctuating levels of protein via compensatory growth responses may have merit. However, additional research is warranted to determine why crowded pigs respond differently than uncrowded pigs to widely fluctuating levels of dietary crude protein.


   Footnotes
 
1 Appreciation is expressed to B. Bohling, B. Duncan, J. Droll, S. Bohlen, and J. Duncan for animal care and diet preparation. Back

2 Correspondence: 1600 Oregon St. (phone: 563-264-4377; fax: 563-264-4132; E-mail: michael_edmonds{at}kentfeeds.com).

Received for publication November 15, 2002. Accepted for publication July 14, 2003.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 


AOAC. 1996. Official Methods of Analysis. 16th ed. Assoc. Offic. Anal. Chem., Arlington, VA.

Atinmo, T., C. Baldijao, K. A. Houpt, W. G. Pond, and R. H. Barnes. 1978. Plasma levels of growth hormone and insulin in protein malnourished vs. normal growing pigs in response to arginine or glucose infusion. J. Anim. Sci. 46:409–416.

Bikker, P., M. W. A. Verstegen, B. Kemp, and M. W. Bosch. 1996a. Performance and body composition of finishing gilts (45 to 85 kilograms) as affected by energy intake and nutrition in earlier life: I. Growth of the body and body components. J. Anim. Sci. 74:806–816.[Abstract]

Bikker, P., M. W. A. Verstegen, B. Kemp, and M. W. Bosch. 1996b. Performance and body composition of finishing gilts (45 to 85 kilograms) as affected by energy intake and nutrition in earlier life: II. Protein and lipid accretion in body components. J. Anim. Sci. 74:817–826.[Abstract]

Campbell, R. G., M. R. Taverner, and D. M. Curic. 1983. Effects of feeding level from 20 to 45 kg on the performance and carcass composition of pigs grown to 90 kg live weight. Livest. Prod. Sci. 10:265–272.

Chiba, L. I. 1994. Effects of dietary amino acid content between 20 and 50 kg and 50 and 100 kg live weight on the subsequent and overall performance of pigs. Livest. Prod. Sci. 39:213–221.

Chiba, L. I. 1995. Effects of nutritional history on the subsequent and overall growth performance and carcass traits of pigs. Livest. Prod. Sci. 41:151–161.

Chiba, L. I., H. W. Ivey, K. A. Cummins, and B. E. Gamble. 1999. Growth performance and carcass traits of pigs subjected to marginal dietary restrictions during the grower phase. J. Anim. Sci. 77:1769–1776.[Abstract/Free Full Text]

Cotlove, E. 1963. Determination of the true chloride content of biological fluids and tissues. II. Analysis by simple, nonisotopic methods. Anal. Chem. 35:101–105.

Critser, D. J., P. S. Miller, and A. J. Lewis. 1995. The effects of dietary protein concentration on compensatory growth in barrows and gilts. J. Anim. Sci. 73:3376–3383.[Abstract]

de Greef, K. H., B. Kemp, and M. W. A. Verstegen. 1992. Performance and body composition of fattening pigs of two strains during protein deficiency and subsequent realimentation. Livest. Prod. Sci. 30:141–153.

Fabian, J., L. I. Chiba, D. L. Kuhlers, L. T. Frobish, K. Nadarajah, C. R. Kerth, W. H. McElhenney, and A. J. Lewis. 2002. Degree of amino acid restrictions during the grower phase and compensatory growth in pigs selected for lean growth efficiency. J. Anim. Sci. 80:2610–2618.[Abstract/Free Full Text]

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