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ANIMAL NUTRITION |
Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada, N1G 2W1
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: amino acid intake • body composition • compensatory growth • pig
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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; Robinson, 1964; Critser et al., 1995), whereas in other studies no or incomplete CG was observed (Kyriazakis et al., 1991; Stamataris et al., 1991; de Greef et al., 1992; Ferguson and Theeruth, 2002; Whang et al., 2003). The phenomenon of CG may be used in commercial pork production to manipulate growth performance (Bikker et al., 1996), carcass characteristics (Oksbjerg et al., 2002), meat tenderness (Kristensen et al., 2002), or nutrient utilization efficiency (Tullis et al., 1986; Whang et al., 2000; Fabian et al., 2004). To fully exploit CG in growing pigs, the impacts of feeding and animal factors on the extent and rate of CG need to be quantified. As outlined by Martínez-Ramírez et al. (2008), CG after a period of AA intake restriction may be represented based on the partitioning of retained energy in growing pigs between body protein deposition (Pd) and body lipid deposition (Ld). These authors suggest that CG and compensatory Pd in growing pigs is apparently constrained by the pig’s upper limit to Pd (PdMax) and may be driven by a target body composition, represented by the ratio between whole body lipid (LB) and whole body protein (PB) content (LB/PB). Previous studies have shown that when pigs are fed AA-limiting diets, the actual Ld to Pd ratio (Ld/Pd) is greater than the desired Ld/Pd, resulting in pigs with LB/PB that are larger than the target LB/PB. When the AA intake restriction is removed, pigs may alter Ld/Pd to achieve a target LB/PB, in which case CG can occur (de Greef et al., 1992).
To further test these concepts, a study was conducted to determine the dynamics of Pd and changes in body composition after sudden changes in AA intake in entire male pigs with high lean-tissue growth potential. The PdMax of this population of pigs was estimated to be 220 g/d (Weis et al., 2004).
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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The University of Guelph Animal Care Committee approved the experimental protocol. A total of 58 pure-bred Yorkshire entire male pigs, from 23 litters and weighing approximately 10 kg of BW, were obtained in 4 blocks from the University of Guelph Arkell Swine Research Station herd and transported to the animal metabolism unit. The pigs were previously fed a well-balanced pig starter diet ad libitum. Pigs were housed individually in fully slatted floor pens (1 x 1.75 m) in an environmentally controlled room (22°C) and were given free access to water via nipple drinkers (Möhn and de Lange, 1998). Pigs were fed a pig starter diet at libitum until they reached approximately 15 kg of BW. At the start of the experiment, at approximately 15 kg of BW and when pigs were between 6 and 7 wk of age, pigs were fed equal amounts of feed twice daily at 0900 and 1600 h. Pigs were weighed weekly to monitor growth rate and to adjust feeding levels. Feed refusals were collected daily and weighed weekly to calculate actual feed intakes. Pigs were monitored twice daily for abnormal behavior and signs of disease.
Experimental Design and Diets
At the start of the experiment and at approximately 15 kg of BW, 4 pigs were sacrificed to determine initial chemical and physical body composition. For the remaining pigs and throughout the experiment, feed intake levels were restricted to 90% of the voluntary daily DE intake (DEi) according to NRC (1998):
At this level of energy intake, pigs were likely maintained within their energy-dependent phase of Pd up to 35 kg of BW (Möhn and de Lange, 1998). At 15 kg of BW, pigs were randomly allotted to 1 of 3 dietary AA levels: control (115% of estimated AA requirements according to NRC, 1998; n = 18 pigs), AA-15% (85% of estimated AA requirements; n = 16 pigs) and AA-30% (70% of estimated AA requirements; n = 20 pigs). Unfortunately, 2 pigs that were supposed to be assigned to treatment AA-15% were assigned to treatment AA-30%. Pigs were exposed to these treatments until they reached 38 kg of BW (restriction phase).
Once pigs reached 38 kg of BW, the start of the realimentation phase, they were fed common nonlimiting diets and were assigned to 1 of 4 target slaughter weights: 38 kg of BW (n = 2 pigs per treatment), 53 kg of BW (n = 3, 2, and 4 pigs for the control, AA-15%, and AA-30% treatment, respectively; unequal numbers to correct for the error made when assigning pigs to treatments at 15 kg of BW), 68 kg of BW (n = 3, 2, and 4 pigs for the control, AA-15%, and AA-30% treatment, respectively), and 110 kg of BW (10 pigs per treatment). Whole body N balance was determined repeatedly in a subsample of pigs (n = 6 pigs per treatment) to monitor the dynamics of Pd during the realimentation phase.
Experimental diets for the control and AA-30% treatments were prepared and pelleted at the University of Guelph feed mill (Table 1). Between 15 and 38 kg of BW, pigs were fed 2 consecutive diets (I and II) while diets were switched at 28 kg of BW. Diets for the AA-15% treatment were prepared by blending the control and AA-30% diets in a 33:67 ratio. In this manner, the 3 dietary treatments represented +15, –15, and –30% of the estimated AA requirements of pigs with superior lean-tissue growth potential according to NRC (1998). The balance among essential AA was maintained constant across treatments and was based on the optimum ratio among dietary AA according to NRC (1998). Therefore, AA represented an approximation of balanced or ideal protein.
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. Serial Slaughter, N Balance, Sample Preparation, and Chemical Analyses
Sampling and analytical procedures were outlined in detail by Martínez-Ramírez et al. (2008). After the restriction phase and when pigs weighed approximately 38 kg of BW, 18 pigs were moved to metabolism crates for N-balance measurements. After 3 d of adaptation, N balance was monitored during 4 periods: period I (40 kg of BW; 4 d), period II (44 kg of BW; 4 d), period III (64 kg of BW; 7 d), and period IV (82 kg of BW; 7 d). Between N-balance periods II, III, and IV, pigs were returned to the floor pens. All pigs involved in N-balance measurements were slaughtered at 110 kg of BW.
Calculations and Statistical Analysis
All the calculations to determine body composition, Ld, Pd, and N retention were described in detail by Martínez-Ramírez et al. (2008) and elsewhere (Möhn et al., 2000; Weis et al., 2004). The statistical analyses were performed by ANOVA according to the GLM procedure (SAS Inst. Inc., Cary, NC) in a complete randomized block design. In this experiment, dietary AA level (n = 3) and block (n = 4; groups of pigs upon arrival) were considered as sources of variation; the effect of litter was deemed not significant (P > 0.10). Initial BW was used as a covariate when growth performance was evaluated. Differences among treatment means were assessed by the Tukey honestly significant difference test. Linear and quadratic contrast analyses were performed to evaluate responses to dietary AA level. Regression analyses using the GLM procedure of SAS were conducted to evaluate linear and quadratic relationships between Pd and d (N-balance study); BW, PB, or LB and d; and the relationship between whole body ash content (AB) or whole body water content (WB) and PB. Probability levels less than P < 0.05 were considered significant, whereas 0.05 < P < 0.10 was considered a trend and P > 0.10 was considered not significant.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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In general, the pigs appeared in good health and no abnormalities in animal behavior were observed. However, for 1 pig in each of the 3 treatments, data were removed for parts of the realimentation phase and from the time that pigs developed a lack of appetite. Data from N balances of 2 pigs on the control diet and one pig from the AA-15% diet obtained during the third N-balance period and 1 from each treatment during the fourth N-balance period were removed from the analysis as well because of lack of appetite. In those pigs, feed refusals exceeded 30% of the daily feed allowance. Values for Pd, Ld, and Ld/Pd derived from serial slaughter data during the first and second part of the realimentation phase are not presented; these values were highly variable and did not differ between treatments (P > 0.10), largely because of the small number of observations per treatment and the small difference between initial and final slaughter BW.
The analyzed protein contents in the experimental diets were similar to anticipated values (Table 1
). However, total lysine content was below anticipated values in most diets, especially in control I (14%) and in grower I and II (10%). These systematic errors reflect an underestimation of nutrient contents in some of the ingredients or a systematic error in analytical procedures. These discrepancies do not influence the relative response to treatments.
The design of the current experiment allowed for the assessment of effects of nutritional history on the dynamic changes in Pd, physical and chemical body composition, and growth performance. This is in contrast to studies in which the impact of N intake during the starter or growing phase on subsequent growth performance was evaluated in a static manner (e.g., Wyllie et al., 1969; Zimmerman and Khajarern, 1973; Campbell and Biden, 1978; Kyriazakis et al., 1991; Whang et al., 2003). In all these studies, growth and nutrient utilization after nutrient intake restriction were evaluated over 1 or 2 specific BW ranges (Campbell and Dunkin, 1983a; Ferguson and Theeruth, 2002). Only Campbell and Dunkin (1983b) evaluated changes in whole body N retention during 5 subsequent periods and up to 75 kg of BW, after AA intake restriction between 1.5 and 15 kg of BW. In other studies (Tullis et al., 1986; Whang et al., 2000; Fabian et al., 2004), the N-balance technique was used to measure N retention, whereas changes in body composition were not measured.
Growth Performance
Growth performance data are presented in Table 2. Initial BW did not differ among treatments (P > 0.10). During the restriction phase, ADG and G:F decreased linearly and quadratically (P < 0.005) with increasing AA intake restriction, whereas total feed intake increased linearly and quadratically (P < 0.05) with AA intake restrictions. At the end of the restriction phase, pigs on the AA-15% and AA-30% diets were 5 and 6 d older, respectively, than pigs on the control diet. Similar results were observed in other studies (e.g., Chiba, 1994, 1995; Critser et al., 1995; Chiba et al., 1999).
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; Fabian et al., 2002; Whang et al., 2003). In similar studies and when pigs were fed ad libitum, Wyllie et al. (1969), de Greef et al. (1992), Chiba et al. (2002), and Fabian et al. (2004) observed that ADFI during the realimentation phase was reduced by 6, 10, 8, and 10%, respectively. Because feed intake was controlled in this study, CG was attributed fully to improvement in feed efficiency and not to treatment effects on feed intake. Similar observations were given by Whang et al. (2003).
When combining the restriction and realimentation phases, AA intake restriction did not affect growth performance (P > 0.10). Moreover, at the final slaughter BW, there were no differences in time on the experiment among treatments (P > 0.10). These results indicate that, based on BW vs. time, this population of pigs showed full CG. Besides Wyllie et al. (1969) and Fabian et al. (2002), no other studies have shown complete CG after AA intake restriction based on BW versus time.
Physical and Chemical Body Composition
Physical and chemical body composition data are presented in Table 3. Across all observations, the sum of chemical body constituents (protein, lipid, ash, and water) contributed to 99.4 ± 0.7% of empty BW (EBW), confirming the adequacy of sampling and analytical procedures. Across slaughter BW, gut fill represented 4.68 ± 1.5% of live BW. This value is close to the value of 5% proposed by ARC (1981) and de Lange et al. (2003).
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) and those of Kyriazakis et al. (1991), indicating that AA intake restriction per se does not effect the weight of visceral organs relative to EBW. In the current study, increased AA intake restriction altered the chemical body composition at 38 kg of BW by linearly increasing LB and LB/PB (P < 0.005) and linearly decreasing AB and WB contents in the EBW (P < 0.05). Wyllie et al. (1969), Zimmerman and Khajarern (1973), Campbell and Biden (1978), Kyriazakis et al. (1991), and Whang et al. (2003) observed similar trends when AA intake was restricted in growing pigs. The distribution of PB between viscera and carcass was not altered (P > 0.10) by AA intake restriction. These results are supported by the findings reported by Martínez-Ramírez et al. (2008) and Whang et al. (2003). In the current experiment, AA intake restriction between 15 and 35 kg of BW successfully reduced growth performance and resulted in fatter pigs at the end of the restriction phase.
During the realimentation phase, previous AA intake restriction did not have any effect on visceral organ weight at each of the 3 slaughter BW (P > 0.10; data not shown). Apparently, a moderate restriction in protein intake does not affect the size of visceral organs, and visceral organ weight is more sensitive to energy intake than protein intake levels (de Lange et al., 2003).
The differences between dietary treatments in chemical body composition observed at 38 kg of BW were reduced to nonsignificant differences when pigs grew from 53 to 110 kg of BW (P > 0.10). These results are illustrated graphically in Figures 1 and 2. Wyllie et al. (1969), Kyriazakis et al. (1991), and Whang et al. (2003) reported similar findings. On the basis of regression analysis, both previous nutrition and slaughter BW did not affect the proportion of LB present in the carcass (P > 0.10; data not shown). Neither nutritional history nor energy intake level (Weis et al., 2004) seems to affect the distribution of LB between carcass and viscera.
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and de Lange et al. (2003) postulated that across BW, the relationship between WB and PB is best expressed by using an allometric relationship, WB = a x PB0.855, with a varying among pig types. The ARC (1981) and Emmans and Kyriazakis (1995) reported that a can vary between 4.89 and 5.06 and that it increases with lean growth potential or mature PB. In this experiment, a was estimated at 5.50 ± 0.06, 5.47 ± 0.10, and 5.47 ± 0.04 for the control, AA-15%, and AA-30% treatment, respectively; these values did not differ among treatments (P > 0.10). According to de Lange et al. (2003), AB can be expressed accurately as a fraction of PB. In the current study, the ratio between AB and PB was 0.156 ± 0.01, 0.161 ± 0.01, and 0.160 ± 0.01 for the control, AA-15%, and AA-30% diet, respectively; these values did not differ among treatments (P > 0.10) and were slightly less than previous estimates (ARC, 1981; de Lange et al., 2003). In general and within BW at slaughter, nutritional history did not have any effect on the relationships between PB and either WB or AB. This reflects the close association among these 3 chemical body components (Schinckel and de Lange, 1996; de Lange et al., 2003). Consequently, the ratio between LB and PB represents a means to characterize body composition in growing pigs. Whole Body Lipid to Whole Body Protein Ratio
Schinckel and de Lange (1996) proposed that constraints on the ratio between LB and PB (minLB/PB or target LB/PB) can be used to represent the effects of pig type, BW, energy intake, and environmental factors on the partitioning of retained energy between Pd and Ld. Values for LB/PB are presented in Table 3. In the current study, the nutrition-induced differences in LB/PB at 38 kg of BW tended to remain up to 68 kg of BW (P < 0.10) and were no longer apparent at 110 kg of BW (P > 0.10). Within each of the 3 dietary treatments, LB/PB changed quadratically (P < 0.05) with increasing BW (Figure 2), whereas across treatments an interaction between treatments and BW (linear, P = 0.05) was observed. These results suggest that the entire male pigs achieved a target body composition (LB/PB) at 110 kg of BW in spite of nutrition-induced differences in body composition at 38 kg of BW.
In previous studies in our laboratory and with entire male pigs of the same population (Weis et al., 2004), it was determined that at 95% of voluntary daily DE in-take (according to NRC, 1998) pigs did not reach their PdMax or just approached their PdMax at approximately 100 kg of BW. Furthermore, in the present experiment, the observed LB/PB for pigs fed the control diet were 0.68, 0.80, and 1.08 for 38, 68, and 110 kg of BW, respectively, and were similar to observed LB/PB at the high energy intake scheme reported by Weis et al. (2004; 0.71, 0.83, and 1.06 at 40, 65, and 90 kg of BW, respectively). This indicates that LB/PB values observed in the present experiment for pigs on the control treatment were similar to target LB/PB values as determined by energy intake (Weis et al., 2004). Therefore, and over the BW range that was evaluated in this study, the entire male pigs on the control diet were likely within the energy-dependent phase of Pd and did not express PdMax, at least until pigs approached the final BW. The ability of the pig to achieve a target body composition after a period of AA intake restriction has been established and documented by other researchers (Wyllie et al., 1969; Kyriazakis et al., 1991; de Greef et al., 1992). The achievement of a target body composition is in contrast with the observation of restricted, scale-fed barrows in a previous experiment (Martínez-Ramírez et al., 2008). Apparently, restricted-fed pigs can achieve the target body composition only within the energy-dependent phase of Pd (i.e., when Pd during the realimentation phase is below PdMax; Figure 3).
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and can be used to explain why target body composition is achieved in some cases and not in others. Body Protein Deposition and Body Lipid Deposition
Observed values for Pd, Ld, and Ld/Pd derived from serial slaughter data are presented in Table 2. The Pd estimated from N-balance observations at the 4 N-balance periods (40, 45, 62, and 82 kg of BW) during the realimentation phase are presented in Table 4 and Figure 3. The Pd values derived from serial slaughter measurements are systematically less than those derived from N balances. This discrepancy can be attributed to incomplete collection of N excretion and body N losses during the measurement of N balances. Similar observations were reported by Martínez-Ramírez et al. (2008) and Möhn and de Lange (1998).
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; de Greef et al., 1992; Whang et al., 2003; Martínez-Ramírez et al., 2008).
During the 3 N-balance periods within the realimentation phase, pigs on the AA-15% diet had greater Pd (P < 0.05) than pigs on the control diet (Table 4). Moreover, trends toward linear and quadratic effects of the previous AA intake level on Pd were observed during the realimentation phase (P < 0.10; Table 4). These results are consistent with other studies (Tullis et al., 1986; Whang et al., 2000; Fabian et al., 2004). However, during the last N-balance period, there were no differences in Pd among the 3 treatments. The latter contributed to a trend for an interactive effect of treatment and N-balance periods on Pd (P < 0.10; Table 4 and Figure 3). Over the entire realimentation phase and based on regression analysis of serial slaughter data, Pd tended to be inversely related to dietary AA level during the restriction period (169 vs. 193 and 199 g/d, P = 0.09, for the control, AA-15%, and AA-30% treatment, respectively). Similar results were obtained by Wyllie et al. (1969), de Greef et al. (1992), and Whang et al. (2003). The differences in Pd among treatments disappeared with increasing BW (Figure 3), whereas Ld did not differ among treatments at any BW range (P > 0.10; Table 2). This resulted in elimination of differences in LB/PB between treatments with increasing BW.
Across the combined restriction and realimentation phase and based on serial slaughter data, Pd was identical among all treatments (P > 0.10; Table 4). Thus, compensatory Pd between 38 and 110 kg of BW was sufficient to fully compensate for nutrient-induced reductions in Pd between 15 and 38 kg of BW. Only in a few studies has complete compensatory Pd been observed (Wyllie et al., 1969; Fabian et al., 2004).
According to NRC (1998), Pd is closely related to the accretion of muscle or lean-tissue growth, the main factor that determines the daily requirements for dietary AA, and one of the main factors determining requirements for dietary energy. Whittemore and Fawcett (1976) and Moughan and Verstegen (1988) suggested that PdMax remains largely constant up to approximately 80 kg of BW in most populations of pigs. Quiniou et al. (1995, 1996) reported, based on experimental observation, that PdMax in Large White pigs was constant between 45 and 100 kg of BW, whereas Möhn and de Lange (1998) showed that PdMax in female Yorkshire pigs was constant between 25 and 70 kg of BW. In young growing pigs, PdMax is generally not achieved, primarily because pigs consume insufficient energy to express PdMax and associated Ld. During this energy-dependent phase of Pd, Pd increases with BW because energy intake above maintenance energy intake increases with BW. The latter is consistent with observed changes in Pd during the 4 consecutive N-balance periods in pigs on the control treatment in the current study. However, in pigs in the AA-15% treatment, Pd did not differ among the 4 N-balance periods (P > 0.10).
During the first 3 N-balance periods, calculated lysine disappearance did not differ among treatments, with treatment means ranging between 17.6 and 26.3% of apparent ileal digestible lysine intake (Table 4). These values are greater than the minimum levels of lysine disappearance presented by Möhn et al. (2000), observed under similar conditions. The latter suggest that lysine (among the first-limiting AA in the experimental diets) did not limit Pd during the first 3 N-balance periods. This indicates that either PdMax or energy intake determined Pd in this population of entire male pigs during the first 3 N-balance periods. However, during the fourth N-balance period, lysine disappearance approached minimum values, indicating that AA intake may have limited Pd. This observation is supported by the temporary reduction in ADG in pigs of approximately 85 kg of BW (Table 2).
On the basis of lysine utilization efficiency and during the first part of the realimentation phase, pigs on the AA-15% diet achieved Pd that approached PdMax and used less energy for Ld than pigs in the control treatment to achieve a target body composition. Kyriazakis et al. (1991) and de Greef et al. (1992) showed that an increase in Pd and a reduction in Ld during the realimentation phase were observed during CG. However, in these studies the dynamics of Ld and Pd, and the reason for incomplete compensatory Pd, were not explained. On the basis of observations in the current study, the maximum rate of compensatory Pd appears to be determined by an upper limit to Pd, likely PdMax, and by the discrepancy between actual LB/PB and target LB/PB. The duration of compensatory Pd is determined by the amount of time required by pigs to achieve target LB/PB. This indicates that during CG, the composition of growth is driven by target LB/PB and not by constraints on Ld/Pd. These findings are consistent with the lack of compensatory Pd observed in barrows (Martínez-Ramírez et al., 2008) under similar experimental conditions. Because of the much lower PdMax in barrows compared with entire male pigs, PdMax was achieved at a much lower BW in barrows on the control treatment. Barrows that were previously fed AA-limiting diets were thus unable to achieve greater Pd than pigs in the control treatment.
On the basis of the growth performance, PB, and N-balance data (Figures 1 and 3), pigs on the AA-15% diet increased Pd more quickly during the realimentation period than pigs on the AA-30% diet. This could be because pigs in the AA-30% treatment were restricted too severely, which may have reduced the pigs’ ability to express PdMax, but this requires further exploration.
In summary, complete CG and compensatory Pd occurred in scale-fed entire male pigs with high lean-tissue growth potential after moderate AA intake restriction between 15 and 38 kg of BW. In spite of a previous AA intake restriction, these pigs were able to achieve the same body composition at 110 kg of BW as compared with pigs that were not exposed to AA intake restriction. Compensatory Pd after AA intake restriction appears to be driven by a target LB/PB, whereas the maximum rate of compensatory Pd appears constrained by the pig’s PdMax or AA intake. Thus, CG in growing pigs reflects merely a repartitioning of body energy retention between Ld and Pd and may be exploited only when pigs are within their energy-dependent phase of Pd.
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Footnotes |
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2 Corresponding author: cdelange{at}uoguelph.ca
Received for publication April 24, 2007. Accepted for publication April 16, 2008.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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