Effects of Dietary Lysine and Energy Levels on Growth Performance and Apparent Total Tract Digestibility of Nutrients in Weanling Pigs

Two experiments were conducted to determine the effects of dietary lysine and energy level on performance and apparent total tract digestibility (ATTD) of nutrients in weanling pigs. In Exp. 1, a total of 288 weaned pigs (initial BW 5.77±0.85 kg) were randomly allotted to 4 treatments (4 replicates per treatment with 18 pigs in each replicate). Experimental diets were fed in the 3 phases: phase I (d 0 to 7), phase II (d 8 to 14) and phase III (d 15 to 28). Isocalorific diets (3,450 kcal/kg) with incremental lysine levels (Phase I: 1.51, 1.61, 1.71 and 1.81; Phase II: 1.35, 1.46, 1.56 and 1.66; Phase III: 1.18, 1.28, 1.39 and 1.49% lysine respectively for T1, T2, T3 and T4) were used as treatments. An increase in the dietary lysine levels linearly improved (p<0.05) the ADG and G:F during phases I, II and III as well as overall study period. The ATTD of DM (d 7 and 28) and CP (d 7, 14 and 28) were linearly improved (p<0.05) with increasing dietary lysine levels. ATTD of ash, Ca and P were not affected by dietary lysine level. In Exp. 2, 64 weanling pigs (initial BW 4.79±0.79 kg) were randomly allotted to 4 treatments (4 replicates per treatment with 4 pigs in each replicate) in a 2×2 factorial arrangement on the basis of BW. Effects of two levels of energy (high, 3,450 or low, 3,350 kcal/kg) and lysine (high or low; 1.70 or 1.50, 1.55 or 1.35 and 1.40 or 1.20% in phase I, II and III diets, respectively) on performance and ATTD of nutrients were investigated. High energy and lysine diets improved ADG (p<0.05) in pigs during phase I, II and III and overall period (p<0.001), while G:F increased (p<0.05) during phase I and overall period. Pigs fed high lysine diets consumed more (p<0.05) feed during phase III and overall period. Additionally, pigs fed high energy diets had greater (p<0.05) ATTD of GE (d 7 and 14), CP (d 7 and 28) and DM (d 28); whereas, pigs fed high lysine diets had greater (p<0.05) ATTD of GE and CP during d 7, 14 and 28. ATTD of ash, Ca and P remained unaffected (p>0.05) by dietary energy and lysine level. However, there was no energy×lysine interaction for any of the measured variables. Results obtained in present study suggested that high energy and lysine level improve the growth performance and ATTD of nutrients in weanling pigs. (


INTRODUCTION
Feed intake and growth performance of growing pigs are determined by energy concentration of the diet (NRC, 1998).Therefore, amino acid requirement of growing pigs should be defined in relation to energy density of the diet.Lysine, the first limiting amino acid for growing pigs has been extensively investigated and reviewed (NRC, 1998).Several investigations on lysine requirement for weaned pigs have yielded variable results (Gatel et al., 1992;Nam and Aherne, 1994;Oresanya et al., 2007;Dneg et al., 2010).The lysine requirement for growing pigs is commonly expressed as lysine: energy ratio, which allows lysine requirements to be suitable for wide range of dietary energy (Main et al., 2008).Furthermore, dietary lysine requirement have been determined at only one dietary energy level (Martinez and Knabe, 1990).However, previous studies contain diverse estimates of the optimum lysine:energy for weaning pigs performing at levels commonly observed in commercial practice (Nam and Aherne, 1994;Smith et al., 1999;Urynek and Buraczewska, 2003;Oresanya et al., 2007;Schneider et al., 2010).Many factors, like genetic variation, nutrition, physiology, environment and management condition could be responsible for variation in requirement, in weanling pigs, but a major variation may be the interactive effects between energy density and lysine intake (Campbell and Dunkin, 1983;Zhang et al., 1984).With the economic importance of energy and amino acid source, the determination of the optimum lysine:energy to get a best performance in weaning pigs is badly needed.Therefore, objectives of these experiments were to investigate the effects of dietary lysine and energy levels on growth performance and apparent total tract digestibility of nutrients in weanling pigs.

MATERIALS AND METHODS
The protocol for the present experiments was approved by the Institutional Animal Care and Use Committee of Kangwon National University (Chunchon, Republic of Korea).
These experiments were conducted at the facility of Kangwon National University farm and the pigs (Landrace ×Yorkshire×Duroc) were housed in partially slotted and concrete floor pens with a pen size of 2.8 m×5.0 m.All pens were equipped with a self-feeder and nipple drinker to allow ad libitum access to feed and water.

Exp. 1
A total of 288 weaned pigs (Landrace×Yorkshire×Duroc, 21±2 d of age, average initial body weight 5.77±0.85kg) were randomly allotted to 4 treatments on the basis of BW.Each treatment had 4 pens with 18 piglets in each pen.Experimental diets were fed in 3 phases, phase I (d 0 to 7; Table 1), phase II (d 8 to 14; Table 2) and phase III (d 15 to 28 Table 3).The four isocalorific (3,450 kcal/kg) diets with incremental lysine levels (phase I: 1.51, 1.61, 1.71 and 1.81; phase II: 1.35, 1.46, 1.56 and 1.66; phase III: 1.18, 1.28, 1.39 and 1.49% lysine respectively for T1, T2, T3 and T4) were used as treatments.All the diets met or exceeded the nutrient requirements as recommended by NRC (1998) and   differed in crude protein and lysine contents.The proportions of indispensable amino acids relative to lysine were above the balanced protein.

Exp. 2
A total of 64 weaned pigs (initial BW 4.79±0.79kg) of mixed sex (48 males and 16 females) were randomly allotted to 4 treatments on the basis of BW in a 2×2 factorial arrangement.Each treatment had 4 pens with 4 pigs (3 males and 1 female) in each pen.Experimental diets were fed in 3 phases, phase I (d 0 to 7; Table 4), phase II (d 8 to 14; Table 5) and phase III (d 15 to 28 Table 6).Effects of two levels of energy (high, 3,450 or low, 3,350 kcal/kg) and lysine (high or low; 1.70 or 1.50, 1.55 or 1.35 and 1.40 or 1.20% in phase I, II and III diets, respectively) on performance and ATTD of nutrients were investigated.All the diets met or exceeded the nutrient requirements as recommended by NRC (1998) and differed in crude protein and lysine contents.The proportions of indispensable amino acids relative to lysine were above the balanced protein.

Experimental procedures, measurements and analyses
The pigs were weighed individually and feed consumption in each pen was measured at the end of each phase in both experiments.Growth performance in terms of average daily gain (ADG), average daily feed intake (ADFI) and gain:feed (G:F) was calculated during the feeding trial.To evaluate the effect of diets on the apparent total tract digestibility (ATTD) of energy and nutrients, 0.25% chromic oxide was included in the diets as an inert, indigestible indicator.The pigs were fed diets containing chromium during the last 7 d of each experiment, and fecal   grab samples were collected from the floor of each pen during the last 4 d.The fecal samples were pooled within pen and dried in an air-forced drying oven at 60°C for 72 h and ground with Wiley mill using a 1-mm screen for chemical analysis.Feed samples of each experiment were collected from every batch, pooled and sub-samples were analysed for proximate chemical compositions.Analysis of experimental diets and excreta was done according to the method of AOAC (1990).Gross energy was measured by a bomb calorimeter (Model 1261, Parr Instrument Co., Moline, IL), and chromium concentration was determined with an automated spectrophotometer (Jasco V-650, Jasco Corp., Tokyo, Japan) according to the procedure of Fenton and Fenton (1979).Amino acid composition of feed samples was determined by HPLC (Waters 486, Waters Corp., Milford, MA) following acid hydrolysis.Methionine and Cys were determined following oxidation with performic acid (Moore, 1963).

Statistical analyses
The data for Exp. 1 were analysed by using the general linear model (GLM) procedure of SAS software (1996).The treatments were the main effects.Pen was used as the experimental unit for the analysis of all the parameters.Linear and quadratic polynomials were evaluated for increasing lysine levels, and the mean separations were analyzed using the Duncan's multiple range test.In Exp. 2, data was analysed by GLM procedure of SAS software (1996) with a 2×2 factorial design contrast.The treatments were the main effects.Pens were used as the experimental unit for the analysis of all the parameters.The p-values compared the differences between the energy levels, lysine levels, and their interaction.Differences were considered statistically significant at p<0.05.

RESULTS AND DISCUSSION
In Exp. 1, during phase I, II and III as well as overall study period, increase in dietary lysine levels linearly improved (p<0.05;Table 7) ADG and lysine intake.Pig fed diet with increasing lysine level showed increase (Linear, p<0.05) in G:F.Results obtained in present study are in good agreement with findings of Schneider et al. (2010) in nursery pigs, in which increase in dietary lysine level from 0.99 to 1.30% showed linear increase in ADG, lysine intake and G:F.Similarly, increasing the dietary lysine level from 1.4 to 1.8% resulted into 10% improvement in ADG of pigs (Owen et al., 1994).Lenehan et al. (2003) reported higher ADG and G:F in pigs fed 1.4% of lysine.In present study there was no effect of dietary lysine level on ADFI of weanling pig.Similar ADFI responses were reported by Campbell and Taverner (1988), who found no difference in voluntary feed intake of pig fed iso-calorific diets varying in lysine content.Zhang et al. (2008) and Schneider et al. (2010) also reported no influence of dietary lysine level on ADFI in pigs.In contrast, Smith et al. (1999) observed decreasing ADFI as the energy density of diets was increased.This variation in feed intake might be due to variation in the energy density of the diet, as feed intake by growing pigs is generally determined by energy density of the diet (NRC, 1998).In Exp. 2, Pigs fed high energy and high lysine diets had greater (p<0.05;Table 8) ADG during phase I, II and III as well as overall study period.Pigs fed high lysine diets showed increased (p<0.05)ADFI during phase II, III and overall study period.Additionally, high energy (phase I and overall study period) and high lysine (phase I, II, III and overall study period) diets improved (p<0.05) the G:F.Increased growth performance with increase in dietary energy and lysine level in present study are consistent with other reports in the literature (Nam and Aherne, 1994;Smith et al., 1999;Oresanya et al., 2007).Lawrence et al. (1994) reported increased growth performance in growing pigs in response to increase in dietary lysine:energy.Castle et al. ( 1994) also observed improved ADG and G:F when lysine:energy was increased from 1.35 to 2.59 g lysine/Mcal DE.Some other studies also reported increase in lysine:energy in growing pig diets improved ADG and G:F (Rao and McCracken, 1990;Chiba et al., 1991).Increase in lysine and energy level in present study showed increase in total and AID lysine intake (p<0.05) during all three phases as well as overall period of experimental feeding.Schneider et al. (2010) observed increased lysine intake with increase in dietary lysine level but reduced lysine intake with increase in energy density of diet.In this study, no interaction effect among energy and lysine levels on any of the growth performance parameters and lysine intake were detected.These findings are in good agreement with Nam and Aherne (1994) who also did not report interaction effect among energy and lysine levels on growth performance in weaning pigs.Similarly, Urynek and Buraczewska (2003) also reported no interaction between energy and lysine levels on growth performance of weaned pigs from 9.1 to 25.7 kg BW.Contrary to present findings, Van Lunen and Cole ( 2001) reported a DE×lysine:DE interaction on growth performance in weaned pigs.Smith et al. (1999) also detected interaction between ME×lysine:ME on growth performance of weaned pig from 10 to 25 kg body weight.Variable performance of pigs among studies might be due to variation in age of pigs, environment and management conditions.Improvement in management, health status and genetic growth potential suggest that existing (NRC, 1998) recommendations of lysine:energy are not sufficient for optimal growth performance in growing pigs.
In Exp. 1, The ATTD of DM (d 7 and 28) and CP (d 7, 14 and 28) were linearly improved (p<0.05;Table 9) with increasing dietary lysine level.Additionally, pigs fed T3 and T4 diets had greater digestibility of DM (d 7 and 28) and CP (d 7, 14 and 28 compared with pigs fed T1 diet.There were no effect of dietary lysine level on ATTD of ash, Ca and P. Similar to present finding, Jin et al. (2010) observed higher digestibility of CP in pigs fed high lysine diet.Cho et al. (2008) also reported increase in CP digestibility with increase in lysine content of diet but no effect on DM, ash, Ca and P digestibility.In contrast, Noblet et al. (1987) demonstrated that lysine addition in low protein diet did not affect protein digestibility.In Exp. 2, pigs fed high energy diet had greater (p<0.05;Table 10) ATTD of GE (d 7 and 14), CP (d 7 and 28) and DM (d 28); whereas, pigs fed high lysine diets had greater (p<0.05)ATTD of GE and CP during d 7, 14 and 28.However, there was no energy level×lysine level interaction effect (p>0.05) on the ATTD of nutrients.Results obtained herein are in good agreements with Lawrence et al. (1994), who reported increase in ATTD of DM and energy with increase in energy density of diet.Increase in energy density and lysine:energy in diet resulted into increase in CP digestibility but no effect on DM digestibility (Cho et al., 2008).In various previous studies, determinations of apparent fecal and ileal digestibility were carried out at different dietary amino acid levels (Holmes et al., 1974;Jorgensen et al., 1984;Knabe et al., 1989).The results from these studies did not allow the establishment of a detailed relationship between the lysine:energy and apparent digestibility.However in present study digestibility of dry matter and crude protein increased linearly with increase in lysine level of diet and digestibility of gross energy and crude protein showed improvement with increase in lysine and energy density of diet.Understanding the effect of increasing dietary lysine and energy is a most important issue in developing cost-effective feeding strategies.
Although lysine and energy requirement of pigs have been well studied, genetics and environment and management may affect an optimum lysine and energy regimen.Present study showed that 1.4% lysine and 3,450 kal ME/kg showed higher growth performance and ATTD of nutrients in weanling pigs.
In conclusion, results obtained in present study suggest that increase in dietary lysine and energy levels shows improvement in growth performance and apparent total tract digestibility of nutrients.

Table 8 .
Effects of dietary energy and lysine levels on growth performance of weaning pigs (Exp.2)

Table 10 .
Effects of dietary energy and lysine levels on apparent total tract digestibility (%) of nutrients in weaning pigs (Exp.2)