Effects of Dietary Metabolizable Energy and Lysine on Carcass Characteristics and Meat Quality in Arbor Acres Broilers

An experiment was performed to evaluate the effects of dietary metabolizable energy (ME) and lysine on carcass characteristics and meat quality in Arbor Acres (AA) broilers from 1 to 56 days of age. A total of 2,970 1-d-old male broiler chicks were randomly allocated to nine dietary treatments (three ME levels in combination with three lysine levels), and dietary ME and lysine concentrations were formulated by varying corn, soybean meal, tallow, and L-lysine sulfate concentrations. Live body weight (BW), carcass weight (CW), dressing percent, breast muscle weight (BMW), yield of breast muscle, muscle color (CIE L*, a*, and b*), pH values 45 min and 24 h postmortem (pH45, and pH24), meat shear force value (SFV), and water loss rate (WLR) were evaluated. Results showed that live body weight and dressing percent increased (p<0.05) as dietary energy increased. Higher dietary lysine content improved breast muscle weight. Neither carcass weight nor yield of breast muscle was affected by dietary energy or lysine content. Higher ME increased the b* value (p = 0.067) and pH24 value (p<0.05), whereas it decreased SFV (p<0.05) and WLR (p = 0.06). Only water loss rate was influenced (p<0.01) by dietary lysine, which was higher in broilers from the high lysine diet as compared to those from medium or low lysine diets. The pH45 value and L* value of breast muscle were not affected by ME or lysine. Significant interaction of dietary ME and lysine was found on a* value of breast muscle. These results indicated that dietary ME and lysine had important effects on breast muscle growth and meat quality, however their effects were different. Different concentrations of dietary ME and lysine might be considered to improve meat quality. (


INTRODUCTION
Poultry selection, aiming to reduce breeding costs by improving production of poultry, has progressed continually since the early 1970s and resulted in a very large increase in growth rate of chickens.At the same time, the growth, structure or overall metabolism of muscle are also modified by such selection, probably resulting in modifications affecting technological and sensory characteristics of meat (Santoso, 2002;Rémignon and Bihan-Duval, 2003).
Nowadays, poultry quality, which is defined by a combination of multiple factors, has become a primary focus for producers, packers, processors, retailers and consumers.Muscle color and texture are always the two most important factors that influence meat quality.Fletcher et al. (2000) stated that cooked product appearance was significantly associated with raw meat color.Moreover, it is suggested that lightness values could be used as an indicator of poultry breast muscle quality for evaluating the incidence of the PSE-like (pale, soft, and exudative) condition (Barbut, 1993;Owens et al., 2000).Meat pH, tenderness and water holding capacity are attributes of muscle texture that have been studied most extensively.Meat pH is determined by muscle glycogen content and its degradation rate.A rapid pH drop results in earlier onset of rigor and greater degree of rigor shortening, which determines the tenderness of meat (Khan, 1974).Muscle contraction is also controlled by the glycogen reserves ante-mortem and their breakdown rate postmortem.Meanwhile, rapid glycogen breakdown results in increased acidification, and at this pH value, usually the isoelectric point of muscle, most proteins in the myofibril become denatured and can precipitate.The relaxed proteins decrease their capacity to hold water which is characterized by high water loss rate (WLR).Muscle glycogen pools might be manipulated through diets and the rate of glycolysis was reduced in pigs fed a muscle glycogen reducing diet (Rosenvold et al., 2003).
Dietary composition and nutrient content are potent regulators of muscle development and metabolism (Grizard et al., 1995(Grizard et al., , 1999)).Studies of dietary factors on meat quality were focused on vitamins and trace minerals.Decreased shear force values were obtained by injecting CaCl 2 into the muscle of lambs (Carpenter et al., 1997;Clare et al., 1997Clare et al., ). D'souza et al. (1998) ) reported that supplementing Mg to diets 5 days before slaughter increased pH value and decreased water drip loss.Addition of Mg to diets increased the redness of the longissimus thoracis muscle of growing-finishing pigs (Apple et al., 2000).Other studies reported that Cr and Fe had different effects on tenderness, water drip loss, and color of poultry meat (Edens, 1997;Ruiz et al., 2000).Dietary composition and/or feed additives have been shown to affect muscle color of pigs (Rosenvold et al., 2001;Stoller et al., 2003), sheep and cattle (Brandt et al., 1992;Boleman et al., 1996;Geay et al., 2001), and meat tenderness of cows (Boleman et al., 1996) and beef steers (Bruce et al., 1991).Conjugated linoleic acid decreased breast muscle redness of broilers (Du and Ahn, 2002).Deficiency in lysine reduced body growth and had an effect on the development of the pectoralis major muscle and the sartorius muscle in growing chickens (Tesseraud et al., 1996a, b).
Despite the relatively important effect of metabolizable energy and lysine on the performance of broilers (Sanz et al., 2000;Ettle et al., 2003;Urynek and Buraczewska, 2003;Hidalgo et al., 2004;Noy and Sklan, 2004;Lopez and Leeson, 2005;Aftab et al., 2007), data concerning the effect of nutrition, such as ME, lysine and their interaction effects, on these muscle attributes of poultry were seldom available (Moran and Bilgili, 1990;Tesseraud et al., 2001;Smith et al., 2002).The purpose of the present experiment was to determine the effects of dietary ME, lysine and their interactions on carcass characteristics and meat quality (pH, color, water loss rate, and meat shear force value), and to determine the optimum ME and lysine concentrations for better meat quality in Arbor Acres broilers.

Animals and diets
In order to evaluate the effects of dietary ME and lysine on carcass characteristics and meat quality in AA broilers, a 3×3 (three levels of ME (low, medium, and high) and three levels of lysine (low, medium, and high)) factorial experiment was conducted.A total of 2,970 1-d-old AA broilers were randomly allocated to nine dietary treatments with five replicates of 66 birds per replicate pen, each equipped with a raised-wire floor.There was no significant difference for initial body weight (BW, 35.63±0.78g) across treatment groups.Broilers were vaccinated for Newcastle disease and infectious bronchitis disease at the hatchery, at 7 and 21 days of age, respectively.All broilers were housed in an environmentally controlled house with temperature maintained at approximately 35°C during the first week post-hatch, then decreased gradually to 25°C for the duration of the trial.Birds received a 24 h lighting regime during the first three days post-hatch, and 23 h lighting with 1 h darkness from 4 days of age onwards.Pens were enlarged whenever needed to provide enough room for normal growth of broilers.Feed and water were provided ad libitum during the whole experiment period.
In the present study, nine corn-soybean meal-based diets comprising three levels of ME in combination with three levels of lysine were formulated (LL, LM, LH, ML, MM, MH, HL, HM, and HH were symbols for diets with different concentrations of ME and lysine).All nutrient contents except for ME and lysine were formulated to meet or exceed the NRC (1994)   respectively.Diets for broilers from 22 to 42 days of age contained 12.96, 13.38, and 13.79 MJ of ME/kg each in combination with 0.9, 1.0, and 1.1% lysine, respectively.Diets containing 12.96, 13.38, and 13.79 MJ of ME/kg in combination with 0.75, 0.85, and 0.95% lysine, respectively, were fed to birds from 43 to 56 days of age.Diet LL, ML, and HL were basal diets, and the concentrations of lysine in diet LM and LH, diet MM and MH, and diet HM and HH were adjusted by adding L-lysine sulfate to the three basal diets, respectively.The composition and nutrient content of basal diets formulated for broilers in different growing phases are shown in Table 2.

Sample collection
At the end of the experiment, two birds with body weights close to the mean were selected from each pen.Feed and water were withdrawn 12 h prior to slaughter.The birds were humanely slaughtered and carcasses harvested.Breast muscle from both sides of the carcass were skinned and deboned for carcass traits, muscle color (L*, a*, b*), pH value, tenderness and water loss rate measurements.

Measurements
Carcass characteristics : Live body weight, carcass weight, and weight of breast muscle from both sides of the carcass were measured.Carcass weight was defined as the weight with feather-scalded, eviscerated carcass (with head, neck, blood, and hocks removed) (Dilger et al., 2006).The dressing percent (carcass weight relative to live body weight) and yield of breast muscle (breast muscle weight relative to carcass weight) was calculated.
Muscle pH : At 45 min and 24 h after slaughter, the breast muscle pH was tested at a depth of 2.5 cm below the surface using a Model PHB-10B meter (Shanghai Kang-Yi Instrument Co. LTD., Shanghai, China).All pH measurements were conducted on the anterior end of the right breast.The pH meter was standardized by a two-point method against standard buffers of pH 4.0 and pH 7.  1976) were obtained 5 min after slaughter from breast muscle, using a hand-held color difference meter (SC-80C,  (Fletcher, 1999).Shear force value : A 12.7 mm (diameter) core was removed from the anterior end of each fillet with attached sampler.The cores were boiled in a temperature-controlled bath to an internal temperature of 70°C.Upon reaching the desired internal temperature, the cores were removed.Each sample was sheared perpendicular to the grain of the muscle fiber using a 25-kg load cell and crosshead speed of 5 mm/s with a Digital Meat Tenderness Meter of Model C-LM3 (Northeast Agricultural University, Harbin, China).Maximum force measured to cut the cores was expressed as kilogram force (kg.f).For each cooked muscle, the core was sheared in 2 locations and the average of the maximum forces was used for data analysis.
Water loss rate : Water-holding capacity, expressed as water loss rate, was measured by applying a load of 2.25 kg on the fillet core.The released water weight was calculated as the difference between the weight of intact fillet and the pressed fillet.

Statistical analysis
The pen was used as experimental unit.Data were analyzed by the GLM procedure of SAS software (SAS Institute, 1998) for a randomized complete block with a factorial treatment design with dietary ME, lysine, and interaction as main effects.The factorial treatment arrangement consisted of three levels of dietary ME and three levels of dietary lysine.If differences in treatment means were detected, the least significant difference (LSD) was applied to separate means.A significance level of p<0.05 was used during analysis and other significance levels were also specified whenever necessary.

RESULTS
The effects of dietary ME and lysine content on carcass traits are presented in Table 3. Dietary energy affected live body weight and dressing percent.As expected, live body weight of broilers increased with the increase of dietary energy.Body weight of broilers fed medium and high energy content was significantly higher (p<0.05)than those fed the low energy diet.Dietary ME had the same effects on dressing percent.The broilers fed high energy diets had higher (p<0.05)dressing percent than those fed low energy diets.Live body weight and dressing percent were not influenced by dietary lysine.Broilers fed medium and high lysine diets had higher (p<0.05)breast muscle weight than those fed low lysine diets whereas dietary energy had no significant impact on the weight of breast muscle.Carcass weight and breast muscle yield were not affected by dietary energy or lysine.There was no interaction effect on any of the parameters.
Table 4 shows the effects of dietary ME and lysine on muscle color (L*, a*, b*), pH value, shear force value and water loss rate.Dietary ME had no significant effects on the breast muscle L* and a* values, though the b* value increased (p = 0.067) with increasing ME.Dietary lysine had no influence on the color of breast muscle.A significant  -----------------------------------------------------Probability value -------------------------------------------------------- interaction was found on the a* value of breast muscle (p<0.05).This result indicated that differences of a* value between different lysine levels in medium energy diets were significantly greater than differences between lysine levels in low and high energy diets.The pH value of breast muscle 45 min postmortem was not affected by dietary treatments.However, dietary energy and lysine content had significant effects on pH value 24 h postmortem, shear force value and water loss rate (Table 4).The pH 24 value increased with the increment of ME content (p<0.01), which was higher in birds fed medium and high ME diets than in those fed a low energy diet.Dietary lysine had no influence on pH 24 .The breast fillets from broilers fed low ME diets had higher (p<0.05)SFV than those fed medium or high ME diets, whereas dietary lysine had no significant (p>0.05)effect on the tenderness of breast fillets.In this experiment, WLR was measured to evaluate waterholding capacity of muscle.Higher WLR meant lower water-holding capacity.The WLR of breast muscle was affected by dietary ME and lysine concentration.The WLR of breast muscle from boilers fed low ME diets were higher (p = 0.06) compared with those fed medium or high ME diets.Water-holding capacity decreased as dietary lysine concentration increased, and was significantly lower (p<0.01) in broilers fed high lysine diets when compared to those fed low or medium lysine diets.No interaction effect was obtained on pH 45 , pH 24 , shear force value and water loss rate.

DISCUSSION
Although an inadequacy of any nutrient has repercussions for the yield of meat or perhaps quality, only a few are of importance in poultry production.In general, these nutrients are energy, protein and phosphorus (Moran, 1999).Effects of dietary energy on the performance of broilers have been studied extensively (Yalcin et al., 1998;Hidalgo et al., 2004;Shyam Sunder et al., 2007) and showed that increasing dietary energy resulted in greater body weight, which was consistent with the present results.High energy levels are linked to high performance while reduction in dietary energy is not always associated with negative effects.Moran (1997) reported carcass quality and skinless-boneless meat yield of male broilers were not impaired when dietary fat was replaced with corn.This result accords with the present experiment.Increasing dietary energy improved body weight, while carcass weight did not suffer from low energy diets.Body fat may account for the increase in body weight of broilers fed high energy diets and carcass weight was not affected by energy.----------------------------------------------------Probability value ------------------------------------------------------------ Sonaiya et al. (1990) showed that male broilers receiving high energy diets had higher carcass weight.These different results might be due to the different breeds of poultry and environmental temperatures used in these experiments.The effect of the dietary energy on dressing percent was supported by Leclercq and Escartin (1987), who stated that increasing dietary energy led to faster growth rate and higher dressing percentage.In the present experiment, dietary energy had no effect on breast meat weight, though Nahashon et al. (2005) reported that breast meat weights of birds fed diets containing 3,150 kcal ME/kg were higher than those of birds fed 3,050 kcal ME/kg diets.
It is well known that dietary amino acids have important effects on carcass characteristics of broilers (Dozier et al., 2000;Gong et al., 2005;Lohakare, et al., 2005).Moran and Bilgili (1990) and Acar et al. (1991) reported live body weight and chilled carcass were not affected by dietary lysine, whereas Tesseraud et al. (1999Tesseraud et al. ( , 2001) ) stated that lysine deficiency reduced the performance as well as muscle weights, and breast meat weight decreased when feeding low density of dietary lysine to chicks at 50 d of age (Kidd et al., 1998).Breast meat yield decreased significantly as lysine content decreased from 1.05% to 0.85% (Moran and Bilgili, 1990;Acar et al., 1991).Some studies reported lysine had no influence on breast and leg muscle weights (Rostagno and Pack, 1995).In our study, only breast muscle weight increased with incremental dietary lysine content.
Glycogen content and its depletion rate post mortem determines pH decline of muscle (Lister et al., 1970), and glycogen in muscle could be manipulated by dietary composition (Rosenvold et al., 2003).Generally, muscle pH has been associated with lots of meat quality attributes, such as meat color, tenderness, water-holding capacity and other characteristics of muscle.Color is one of the most important quality attributes of poultry muscle or meat product for consumer acceptance.Mugler and Cunningham (1972) reviewed many factors influencing poultry meat color, such as bird sex, age, strain and processing procedures.However, limited studies were available expatiating nutritional aspects and their effects on meat quality and the PSE condition.Smith et al. (2002) reported that wheat-based diets increased broiler breast lightness (L*) and yellowness (b*) and decreased redness (a*) compared to milo-and corn-based diets.Extra dietary supplementation of tryptophan reduced incidence of PSE meat (Adeola and Ball, 1992).Boulianne andKing (1995, 1998) reported that pale fillet had significantly greater lightness value, less redness and greater yellowness, whereas dark fillets had lower lightness and yellowness.In the present study, higher ME increased the b* value of breast muscles whereas, lysine had contrasting effects on b* value of breast muscle such that higher lysine concentration decreased muscle yellowness.The functioning mechanism of energy and lysine on the color of muscle remains unclear, and whether the effect was due to pigments present in feed ingredients or changes in protein metabolism resulting from dietary lysine content needs further study.El Rammouz et al. ( 2004) reported ultimate pH (24 h postmortem) was significantly correlated with lightness (r = -0.37)and yellowness (r = -0.36).Livingston and Brown (1981) reported higher muscle pH resulted in darker breast meat.Dark fillets had significantly lower lightness, higher redness, lower yellowness, and higher pH values (Boulianne andKing, 1995, 1998;Allen et al., 1997).These findings were confirmed by Yang and Chen (1993).The above results were consistent with the present research, in which increased lightness was associated with higher yellowness and decreased redness.
Much research has been conducted to study the factors influencing meat tenderness and water-holding capacity (Fletcher, 2002).Genetic stock and selection (Smith, 1963), age, sex, location (Castaneda et al., 2005), pre-and postslaughter chilling (Alvarado and Sams, 2000) and postmortem metabolism (Skarovsky and Sams, 1999) were factors affecting quality of muscle.About 88 to 95% of water in the muscle is held intracellularly within the space between actin and myosin filaments (Ranken, 1976;Offer and Knight, 1988).Water-holding capacity determines the juiciness, flavor and tenderness of meat (Wood, 1993).Lactic acid accumulation and the decline in pH post mortem result in protein denaturation and an overall decrease in muscle water-holding capacity.On the other hand, divalent cations in the sarcoplasm, during the rigor mortis period, bind to the reactive groups on adjacent protein chains, reducing the electrostatic repulsion between negatively charged groups that maintain their separation (Wismer-Perdersen, 1986).This reaction reduces the space available for water to be retained intramuscularly.Rosenvold et al. (2003) reported that a higher digestible energy diet induced a reduction in total glycogen stores, which resulted in a higher ultimate pH value.This may account for the lower water loss rate and resultant higher tenderness of breast muscle from birds fed a high energy diet in the present experiment.Another attribute of energy to tenderness of muscle is intramuscular fat.The decrease in shear force value with dietary energy might be due to increased muscular fat content and altered glucose metabolism by decreasing the translocation or expression of glucose transporter-4 (Clarke, 2000).Lyon et al. (2004) also reported that breast fillets from wheat-fed birds required more force to shear compared with breasts from corn-fed birds.
It is clear that dietary lysine content affects the performance and carcass characteristics of broilers.Relatively little research has been conducted to study the density of dietary lysine on the meat quality of broilers.Apple et al. (2004) reported that lysine content had no effect on the pH, drip loss, firmness score and a* value of LM in pigs, and increased the L* value and decreased the b* value.Cameron et al. (1999) found that lower lysine density produced redder and more yellow pork meat than higher density of dietary lysine.No influence of lysine on ultimate pH, shear force value and meat color was observed in this study, whereas increasing dietary lysine content significantly decreased water-holding capacity in the breast muscle.However, the relationship between muscle lysine metabolism, protein turnover and muscle water-holding capacity needed further study.
According to the results obtained in the present study, dietary ME and lysine had significant effects on carcass characteristics and meat quality.These parameters responded to dietary ME and lysine in different ways.Therefore, higher body weight and dressing percentage would be obtained by feeding a higher level of dietary ME to broilers, higher lysine density would produce more breast meat and medium dietary energy and lysine level would produce more tender meat.
LL = Low energy low lysine; LM = Low energy medium lysine; LH = Low energy high lysine; ML = Medium energy low lysine; MM = Medium energy medium lysine; MH = Medium energy high lysine; HL = High energy low lysine; HM = High energy medium lysine; HH = High energy high lysine.
0. Muscle color : The CIE L* (lower values indicate darker color), a* (larger positive values indicate more red color), and b* (higher value indicates more yellow color) values (CIE，Commission Internationale de 1'Eclairage,

Table 1 .
Dietary ME and lysine levels for Arbor Acres broilers in different growing phases 1 LL to HH represented nine diets with different energy and lysine concentrations.

Table 2 .
Composition and nutrient content of basal diets 1 for broilers in different growing phases Kangguang apparatus Co. LTD., Beijing, China), with an illuminant D65 and 10° standard observer.Five particular spots of muscle free of hemorrhagic, ecchymotic lesions or any other abnormal discoloration were measured on each muscle

Table 3 .
Effects of dietary ME and lysine on live body weight, carcass weight, breast muscle weight, yield of breast muscle and dressing percent of 56 day-old broilers

Table 4 .
Effects of dietary ME and lysine on the color (L*, a*, b*), pH value 45 min and 24 h postmortem, shear force value (SFV) and water loss rate (WLR) of breast muscle of 56 day-old broilers