Ractopamine and lysine levels on performance and carcass characteristics of finishing pigs

It was evaluated the effect of diets supplemented or not supplemented with ractopamine and digestible lysine on the performance and carcass characteristics of finishing pigs. A total of 50 barrows and 50 gilts (90.2 kg ± 3.5 kg) were used. In the growth performance trial, a randomized block design was utilized in a 5 × 2 factorial arrangement, consisting of five levels of digestible lysine (0.68; 0.78; 0.88; 0.98 and 1.08%) and two levels of ractopamine (0 and 5 ppm), totaling ten diets and five replications. In a study of carcass characteristics, the same design and levels of lysine and ractopamine were used, but another factor (sex of animalsfemale and male) was included, totaling 20 treatments, each one with five replicates. Except for lysine daily intake, it was not observed effect of levels of digestible lysine. The supplementation with ractopamine improved daily weight gain and feed conversion but it did not affect the average feed intake. A greater loin depth and higher yield of carcass meat was obtained in gilts, regardless to supplementation with ractopamine, and also in the males fed ractopamine. The ractopamine improved the rib-eye area but it did not affect the yield and carcass length neither thickness of subcutaneous fat. The levels of digestible lysine did not affect carcass characteristics in either sex. It was found that sex had effect on backfat thickness, which was lower in the carcasses of gilts. The use of 5 ppm ractopamine improves animal performance and carcass characteristics of barrows. The level of 0.68% digestible lysine is sufficient for pigs of both sexes fed diets supplemented with or without ractopamine to show maximal performance and a good carcass composition.


Introduction
The use of ractopamine supplementation in diets of finishing pigs is restrained by the amount of protein and amino acids in the diet.According to Xiao et al. (1999), diets supplemented with ractopamine must receive a minimum of 16% CP (crude protein) and 30% more lysine than a typical diet to achieve significant results in performance and carcass quality.Therefore, ractopamine has been included in diets with 16% CP for pigs weighing from 41 to 109 kg (Apple et al., 2004).However, to obtain an ideal response to the use of this nutrient additive splitter, it is also necessary to provide adequate levels of amino acids in the diet to support the greatest weight gain in meat (Silveira, 2007).Pérez et al. (2006) studied the effect of lysine (0.95, 1.05 and 1.15% total lysine) and ractopamine (0 and 10 ppm) on characteristics of the carcass.The authors found lower backfat thickness on the 10 th rib when they used 1.15% total lysine and 10 ppm of ractopamine and observed a synergistic effect.Marino et al. (2007a) also studied the interaction of two digestible lysine levels (0.67 and 0.87%) and ractopamine (0 and 5 ppm).The authors observed that the effect of ractopamine on loin depth is greater in diets containing 0.87% digestible lysine in barrows of approximately 85 kg that are selected for high lean gain.
Based on these results, levels of lysine can restrict the action of ractopamine, especially in pigs selected for high lean deposition, because the level of lysine is directly responsible for protein synthesis and subsequen deposition of muscle tissue.However, a surplus of lysine may also restrict the benefits provided by β-adrenergic agonists because these amino acids should compete for sites of absorption and catabolism of these amino acids surpluses at the expense of increased protein synthesis.
Thus, the purpose of this study was to investigate the effect of ractopamine, associated with different digestible lysine levels, on performance and carcass characteristics of finishing pigs weighing from 90 to 118 kg.

Material and Methods
The experiment was carried out from February to May 2008 in the Centro Experimental de Suínos do Departamento de Zootecnia, Universidade Federal de Lavras (UFLA), in Lavras, southern region of Minas Gerais.During the experimental period, the average temperature was 21.0°C with recorded minimal and maximal temperatures of 16°C and 26°C, respectively.
The study population consisted of 50 barrows and 50 gilts.They were hybrids (Topp × C-40) selected for high lean gain with initial weight 90.20 kg ± 3.5 kg and final weight 117.80 kg ± 4.1 kg.
In the performance assay, the experimental design was randomized blocks in a 5 × 2 factorial, composed of five levels of digestible lysine (0.68; 0.78; 0.88; 0.98 and 1.08%) and two levels of ractopamine (0 and 5 ppm), totaling ten diets with five replicates of two animals per experimental plot.
In the evaluation of carcass traits, the experimental design was also randomized blocks but an additional factor, the sex of the animal, was included, resulting in a 5 × 2 × 2 factorial composed of five levels of digestible lysine (0.68; 0,78; 0.88; 0.98 and 1.08%), two levels of ractopamine (0 and 5 ppm) and two sexes (male and female), totaling 20 treatments and five replicates of one animal per experimental plot.Initial weight was the criterion used to form the blocks.
The diets were formulated based on corn and soybean meal to meet the minimal requirements suggested by Rostagno et al. (2005) for barrows at 100 to 120 kg with high genetic potential and superior performance, with the exception of crude protein (16% CP), lysine, methionine and threonine.Concentrations of methionine (62%) and threonine (67%) were adjusted to fit the ideal AA profile in relation to lysine (100%).However, in diets with 0.68% digestible lysine, it was not possible to maintain the relationship to fit the ideal profile in relation to lysine because the use of corn and soybean meal provided unnecessary amounts of methionine and threonine (Table 1).
The diets and water were given ad libitum for a period of 28 days.The pens were cleaned every day, and feed was provided twice daily.Food wastes were weighed to determine consumption of each pen.
For the determination of weight gain, pigs were weighed at the beginning and at the end of the experiment.The average feed conversion was obtained using the ratio between feed intake and weight gain during all experimental period.
The variables analyzed for performance were final weight, average daily weight gain, average daily feed intake, feed conversion and intake of lysine.
At the end of the experimental period, animals underwent fasting from solids for a period of 16 hours.After fasting, all animals were weighed and slaughtered.
Following slaughter, evisceration was completed, and the carcasses were sawed in half lengthwise, weighed and then cooled at an average temperature of 4°C for 24 hours.
After 24 hours of cooling, the left half of the carcass of each animal was sectioned at the last rib to measure the longissimus muscle area.All measurements were made in accordance with the standards of the Associação Brasileira dos Criadores de Suínos (ABCS, 1986).
Data of the diets were subjected to analysis of variance using the computer program SISVAR developed by Ferreira (2000).When interaction among factors was not observed, polynomial regression for the levels of digestible lysine and F tests for levels of ractopamine and sex was applied.

Results and Discussion
There was no interaction between ractopamine and digestible lysine levels for the studied variables (P>0.05), which is in agreement with the results obtained by Marino et al. (2007a), who studied two levels of lysine (0.67 and 0.87%) and ractopamine (0 and 5 ppm) for barrows from 85 kg to 120 kg (Table 2).
The highest average daily weight gain and better feed conversion (P< 0.05) was observed in animals that were fed ractopamine.The increase in average daily weight gain was 6.6% for animals that consumed ractopamine, which is a result similar to that reported by Amaral et al. (2009), in which ractopamine improved 8.4% with this variable.Carr et al. (2005a) and Marino et al. (2007b) also demonstrated a positive effect on average daily weight gain with ractopamine in diets for finishing pigs.
However, in other studies, Pozza et al. (2003), Carr et al. (2005b) and Marino et al. (2007a) observed no effect of ractopamine on this variable.This divergence of results may be explained by the interaction among ractopamine, genotype and nutritional management (Dunshea et al., 1993).
The average daily feed intake was not affected (P>0.05) with the use of ractopamine.Similar results also occurred in studies by Marino et al. (2007a, b), Amaral et al. (2009) and Kiefer & Sanches (2009).According to these authors, supplementation in finishing pig diets with ractopamine improves weight gain and efficiency of lean meat without changing the daily diet.However, these results differ from  2 Provided per kilogram of diet: Fe -26.25 mg; Zn -78.0 mg; Mn -41.85 mg; Cu -15.75 mg; I -0.37 mg; and Se -0.30 mg. 3 Cloridrate of Ractopamine was added at the expense of caolim to make diets with 5 mg/kg ractopamine.
those observed by Yen et al. (1990) and Carr et al. (2005b), who found reduction of the average daily feed intake of about 10%.
However, the daily feed intake improved by 10% with ractopamine added to the diet of pigs.Similar results were found by Carr et al. (2005a), Marino et al. (2007a, b) and Amaral et al. (2009).Based on these results, we can infer that pigs fed diets supplemented with ractopamine have more efficient use of feed per unit weight gain than pigs that are fed diets without supplementation.
According to Kessler (2001), the type of feed is highly correlated with variables representing the gain of lean tissue and, therefore, it persists as a performance measure and it is used as benchmark to evaluate the efficiency of production systems for pigs.
Overall, the improved feed indicates a change in metabolism induced by ractopamine with a possible change in the composition of the weight gain increasing the deposition of muscle tissue and, because of the partition of nutrients, reducing fat deposition (Schinkel et al., 2003).This change improves the efficiency of the weight gain from the feed because the synthesis of lean tissue requires less energy than fat (Zagury et al., 2002).
The levels of digestible lysine in the diet of finishing pigs did not have an influence (P>0.05) on performance.The results of average daily weight gain were similar to those obtained by Oliveira et al. (2003a,b) who observed pigs of 110 to 125 kg and 95 to 110 kg.However, the results differ from those reported by Abreu et al. (2007), who observed a quadratic effect of diets on average daily weight gain, where the maximal response was obtained with 0.87% lysine and 3,250 kcal/kg, which corresponded to a daily intake of 24.67 g/day.
Several authors, such as Arouca et al. (2005) and Abreu et al. (2007), also found no significant variation in the feed intake of pigs due to levels of lysine, indicating that the deficiency or excess of amino acid in the diet does not influence feed intake of pigs.
However, Chen et al. (1999) and Oliveira et al. (2003b) reported a reduction in feed intake due to increased levels of lysine in the diet for pigs in the finishing phase up to 120 kg.According to Henry (1985) and D 'Mello (1993), the amino acid imbalance results in a characteristic reduction in feed intake as one of the symptoms.In this study, the imbalance of amino acids was prevented by supplementation with synthetic amino acids (DL-methionine and L-threonine) to the extent that the levels of lysine were increased to maintain the relationship between amino acids and lysine in the diet.
Similarly, for the variable feed, Moreira et al. (2002) also found no effect of lysine level on feed intake.Contrasting with the results observed in this study, several authors (Cline et al. 2000;Fabian et al., 2001) found a positive effect of lysine levels on the efficiency of feed utilization for weight gain in pigs in the finishing phase with final weights above 100 kg.Ractopamine and lysine levels on performance and carcass characteristics of finishing pigs There was an effect of different levels of lysine (P< 0.05) on the intake of lysine, which increased linearly.The increase between the lowest and highest levels of lysine used in this experiment was 34.11%.Since the average daily consumption of the diet was not influenced by the levels of lysine, the increase in the consumption of lysine was occasioned by the level of dietary lysine.Because there was no difference in the performance, the level of 0.68% digestible lysine (23.04 g/day) was sufficient to meet the requirements of finishing pigs from 90 to 118 kg whether or not the diet was supplemented with ractopamine.
There was no effect of ractopamine (P>0.05) on the yield, carcass length or the thickness of subcutaneous fat (Table 3).In agreement with this work, several authors observed that ractopamine did not affect yield (Marino et al., 2007a, b;Amaral et a., 2009), carcass length (Carr et al., 2005a, b) or backfat thickness (Weber et al., 2006;Marino et al., 2007a).However, reductions in backfat thickness with the supplementation of ractopamine in the diet were observed by Marino et al. (2007b) and Amaral et al. (2009).
An increase was observed (P<0.05) from 4.25% in the longissimus muscle area when the additive β-adrenergic receptor was used.Weber et al. (2006) and Amaral et al. (2009) also observed this increase, but on the orders of 11.18% and 21.4%, respectively.
There was an interaction between the levels of ractopamine and the sex of the animals for the variable depth of loin and meat yield in carcass of finishing pigs (P<0.05).The greater loin depth and better carcass meat yield was obtained in the carcasses of females that were fed diets supplemented with or without ractopamine and steers receiving ractopamine (Table 4).These results demonstrate greater efficiency in the use of ractopamine in castrated males compared to females.These pigs tend to deposit fat earlier, and the function of â-adrenergic agonists in reducing lipogenesis and increasing protein synthesis becomes more evident.Marino et al. (2007b) observed a 6.5% increase in loin depth and a 1.71% increase in carcass meat yield, while Zagury (2002) reported minor increases in pigs that were fed diets containing 5 ppm of ractopamine.These results show the efficiency of ractopamine as a divider of nutrients at increasing the rate of protein deposition by promoting an increase in the loin eye area, loin depth and yield of carcass meat, especially in barrows.
When evaluating the effects of ractopamine on carcass characteristics of pigs, other authors found no effect on the longissimus muscle area (Mimbs et al., 2005), loin depth (Marino et al. 2007a) or yield of carcass meat (Armstrong et al., 2004, Marino et al., 2007a) from barrows, which may be related to genetics and possibly to the different weights used among papers.
The inclusion of different levels of dietary lysine did not affect carcass characteristics of males and females at termination (P>0.05),irrespective of whether they had been or not supplemented with ractopamine.and Arouca et al. (2005) found no effect of lysine levels in diets on carcass traits of finishing pigs.However, in the study by Abreu et al. (2007), the carcass yield was linearly influenced by levels of dietary lysine (0.70, 0.80, 0.90 and 1.00%), and the lowest level of this amino acid produced better carcass yield.Cline et al. (2000) also observed a linear decrease in carcass yield.
For backfat thickness, several authors observed no effect of lysine level (Moreira et al., 2002, Oliveira et al. 2003ab;Arouca et al., 2005).However, Cline et al. (2000) and Marino et al. (2007a) observed a linear decrease of this variable as levels of this amino acid increased.
Similar to the results for longissimus muscle area obtained in this study, Oliveira et al. (2003b) and Abreu et al. (2007) also found no effect of lysine levels in the diet.The difference in the ability of deposition of the carcass meat of animals used in the work previously cited may have contributed to the variation in the resulting of longissimus muscle area.By studying the body composition of pigs from 25 to 152 kg in five genetic populations, Wagner et al. (1999) found that the longissimus muscle area ranged from 27.68 to 35.91 cm 2 in barrows slaughtered at 114 kg.
No difference (P>0.05) was observed between levels of lysine when the percentage of carcass meat was analyzed.This result was similar to that achieved by Arouca et al. (2005), Fontes et al. (2005) and Abreu et al. (2007), who observed that levels of lysine do not affect this variable.However, Cline et al. (2000), Marino et al. (2007a), Zangeronimo et al. (2009a) and Zangeronimo et al. (2009b) observed that diets supplemented with increasing levels of this amino acid (0.80, 0.95, 1.10, 1.25, 1.40% total lysine and 0.67 and 0.87% lysine, respectively) linearly increased the percentage of meat.
The average yield of meat obtained in this study was 58.28%, similar to values (58.2%) reported by Varley (2001) and reported (57.2%) by Abreu et al. (2007).
An effect of sex on carcass characteristics was observed (P<0.05) in backfat thickness and carcass meat yield.The backfat thickness was lower and the carcass meat yield was greater in females than in barrows.Similar results were obtained by Latorre et al. (2004), Amaral et al. (2009), Cantarelli et al (2009a) and Cantarelli et al. (2009b).By studying the effect of sex on carcass characteristics of pigs with high weights, Latorre et al. (2004) considered that the influence of hormonal activity, the higher basal metabolism and the reduced consumption capacity of females may explain these results.Moreover, the barrows are more precocious than females regarded to deposition of fat in the carcass.
Ractopamine and lysine levels on performance and carcass characteristics of finishing pigs 0.68% (i.e., 23.04 g/day) is enough to reach maximal performance and suitable carcass yield for pigs of both sexes, regardless whether the pig is receiving or not ractopamine.

Table 2 -
Main effect means for growth performance variables, measured at 28 days of fed either ractopamine -with supplemented or no-supplemented diets, and the effects of digestible lysine level in finishing pigs De la Llata et al. (2002) 1 Within treatment coluns, means with different lower case letters differ (P<0.05) by F test.

Table 3 -
Carcass yield, carcass length and backfat thickness of barrows and gilts fed either ractopamine-with supplemented or no-supplemented diets with differents levels of digestible Lysine level