Levels of digestible methionine + cystine in diets for high genetic potential barrows from 95 to 125 kg 1

This study was carried out to evaluate the effects of increasing levels of digestible methionine+cystine on performance and carcass composition of high genetic potential barrows for lean deposition. Sixty-four barrows with initial weight of 95.46 ± 1.09 kg were allotted to a completely randomized block design, with four levels of digestible methionine+cystine (0.427, 0.466, 0.504, and 0.545%, corresponding to the digestible methionine+cystine:digestible lysine ratios of 57.0, 62.0, 67.0 and 73.0%, respectively), with eight replicates, and two animals per experimental unit. Experimental diets and water were provided ad libitum until the end of the experimental period when pigs reached 125.21 ± 2.49 kg. Levels of digestible methionine+cystine did not affect daily intake, daily weight gain and feed conversion of the animals, but they affected daily intake of digestible methionine+cystine which increased linearly. Levels of digestible methionine+cystine did not affect carcass weight, meat amount, backfat thickness at P2, and daily meat deposition. The digestible methionine+cystine level of 0.427%, corresponding to the digestible methionine+cystine:lysine ratio of 57.0% and to a daily digestible methionine+cystine intake of 14.20 g/d, provides the best performance and carcass traits for high genetic potential barrows in the phase of 95 to 125 kg.


Introduction
The growing demand of consumers for a healthy pig meat has been increasing the interest of pig producers and pork industries in slaughtering pigs with higher amount of meat and less fat in the carcass.Meeting this demand has been made possible through genetic selection resulting in lines of pigs with higher R. Bras. Zootec., v.40, n.3, p.581-586, 2011 potential for protein accretion and less fat deposition (Moura et al., 2006).
The production of these new commercial lines makes it viable to the meat industries to slaughter heavier pigs, with higher carcass yield and weight of the major commercial cuts without significant alteration in the percentage of these cuts (Irgang & Protas, 1986).Slaughtering pigs at heavier weights also results in an increase of meat production with no need to change the number of sows, leading to a 20 to 30% increase in the meat supply, therefore improving the income of the producer (Faccin, 1997).
This market tendency for animals with higher weights at slaughter and the introduction of commercial lines specialized in lean meat accretion require nutritionists to update the amino acids requirement of pigs from 95 to 125 kg (Kiefer et al., 2005).
The growing rate and efficiency of pigs can be impaired by an intake of amino acids above or below the amount required by the animals.However, an adequate level of amino acid in the diet can improve feed efficiency and increase both growth rate and profit (Kiefer et al., 2005).
According to the NRC (1998), pigs with high genetic potential have daily protein accretion rate equal or higher than 350 g/day which results in higher requirements of amino acids for maintenance and growth.Among these amino acids, methionine+cystine stands out in the maintenance functions for being engaged in the renewal of intestinal tissues and as precursor of substances with various biological functions.Methionine is important in the biosynthesis of creatine, carnitine, poliamines, epinefrine, choline, and melatonin (Baker, 1991).Cystine participates in the structure of many proteins such as in the hormone insulin, in the immunoglobulin, and for linking polypeptide chains by disulfide bonds (Baker, 1991).
There are much information about lysine requirement of pigs from different genetic groups, categories and sex.However, there is a lack of studies on requirements of sulfur amino acids for late finishing pigs.
Accordingly, this work was conducted to evaluate the effects of different dietary methionine+cystine levels on performance and carcass traits of castrated male pigs with high genetic potential for meat deposition from 95 to 125 kg.

Material and Methods
The experiment was carried out at the Fazenda Experimental Vale do Piranga, of the state-owned Empresa de Pesquisa Agropecuária de Minas Gerais -EPAMIG (Oratórios, Minas Gerais, Brazil), during September and November of 2005.
Sixty-four commercial hybrid male pigs (PIC) with high genetic potential for meat deposition were used allotted in a completely randomized block design with four treatments, eight replicates, and two pigs per experimental unit which was represented by the pen.Body weight was used as criterion in the formation of the blocks (heavy pig vs. light pig).
The ratios between lysine and the other amino acids in the basal diet were checked in order to insure that in all treatments no other amino acid except methionine was limiting in the diet.When the amino acid ratios where being evaluated, it was considered those suggested by Fuller (1996) in the ideal protein for 50 to 110 kg pigs (threonine 70, valine 68, methionine+cystine 65, isoleucine 60, leucine 100, fenilalanine+thyrosine 95, histidine 32, tryptophan 19, arginine 30, and lysine 100).DL-methionine was incorporated into the diets in replacement of glutamic acid proportionally to their nitrogen concentrations.
Pigs were housed in pens with semi-automatic feeders, drinkers, and concrete floor.The thermal environment inside the facility was monitored daily by using minimum and maximum thermometer Pigs were fed ad libitum and water was provided throughout the experimental period.Daily feed waste and animals were weighed weekly to calculate feed intake, daily weight gain, feed conversion, and methionine+cystine intake.
At the end of the experiment, when pigs reached 125.21 ± 2.49 kg, they were weighed after eighteen hours of fasting and then sent to be slaughtered in a commercial meat industry (FRIVAP).Pigs were electrically stunned followed by exsanguinations.
The carcasses were boiled, shaved with flame thrower, eviscerated, weighed, and evaluated for backfat thickness and amount of meat by using apparatus to carcass classification with Henessay Grading Probe (HGP-4), in accordance with procedures used in the meat industry.
Daily meat deposition (DMD) was estimated by using the data of initial weight of the animal (IW), carcass yield backfat thickness at P 2 , amount of meat, carcass weight, and daily meat deposition.
Performance and carcass traits data were analyzed using the procedures for analysis of variance and regression contained in the Sistema para Análises Estatísticas e Genéticas (SAEG), developed at the Universidade Federal de Viçosa (UFV, 2000), version 8.0, using the procedures for variance and regression analysis, according to the following statistical model: Y ijk = μ + B i + T j + e ijk , where: Y ijk = characteristic observed; μ = overall mean of the characteristics; B i = effect of block i; i = 1, 2... e 8; T j = effect of methionine+cystine level j; j = 1, 2... e 4; e ijk = random error associated with each observation.
Estimates of methionine+cystine requirements were determined through linear or quadratic regressions, or by the discontinuous Linear Response Plateau (LRP) model contained in SAEG (UFV, 2000), as the best fit for each variable and taking into account the biological behavior of each animal.
(CY), estimated carcass weight (SCW), carcass lean meat percentage (CLM), estimated meat amount (EMA), final meat amount (FMA), initial estimated meat amount (IEMA), and days in the experimental study (D), calculated by using the equations: The values of carcass yield were obtained using the data of Rossoni et al. (2008) in which the carcass yield was obtained using the Método Brasileiro de Classificação de Carcaça (MBCC), considering the relationship between hot carcass weight and final body weight of the animal whereas the meat percentage in the carcass was determined according to the methodology used by the meat industry (FRIVAP).

Results and Discussion
During the experimental period, the minimal and maximal temperatures inside the facility corresponded to 27.88 ± 3.75 o C and 19.13 ± 1.5 o C, respectively.Considering that according to Perdomo (1994), the range of thermoneutral temperature for finishing pigs is between 12 and 18°C, so it can be inferred that pigs were subjected to periods of heat stress.
The digestible methionine+cystine levels in the diets did not influence (P>0.05)daily feed intake (Table 2).In studies carried out with finishing pigs, Loughmiller et al. (1996), Santos et al. (2007), andPena et al. (2008) did not observe significant variation in the voluntary feed intake of the animals by increasing the dietary digestible levels of methionine+cystine, neither.
On the other hand, Loughmiller et al. ( 1998) evaluated sulfur amino acids levels in diets for finishing female pigs and found significant alteration in the daily feed intake of animals.Based on the results of the studies cited above, it can be assumed that sex of the animal is one factor that can influence the feed intake pattern due to the variation in the dietary levels of methionine+cystine.
Thus, the daily feed intake pattern obtained in this study by increasing the levels of dietary methionine+cystine confirmed the report of Edmonds and Baker (1987) that pigs can tolerate considerable excess of methionine in the diet without presenting significant variation in feed intake.
As the average daily feed intake of pigs in this study corresponded to 3210 g, it can be inferred that periods of high temperatures that pigs were subjected to were not sufficient to compromise their voluntary feed intake, based on the feed intake value of 3100 g/day suggested by Rostagno et al. (2005) for this animal category.
Dietary methionine+cystine levels influenced (P<0.01)methionine+cystine intake which increased linearly according to the equation: Y ^ = 2.7023 + 26.9185 X (r 2 = 0.98).Similarly, Santos et al. ( 2007) also observed linear increase in the digestible methionine+cystine intake of finishing pigs fed different levels of these amino acids in the diets.The result obtained in this study can be justified by the fact that the voluntary feed intake of pigs did not vary significantly among the levels of amino acids evaluated.
There was no effect (P>0.05) of methionine+cystine levels in the daily weight gain of pigs.Similar results were observed by Grandhi and Nyacothi (2002) and Pena et al. (2008), who also found no variation in the daily weight gain of pigs in the finishing phase when levels sulfur amino acids were increased in the diets.
However, Loughmiller et al. (1998) and Santos et al. ( 2007) observed significant variation in the growing rate of finishing pigs by increasing the levels of methionine+cystine in the diets.
Feed conversion was not influenced (P>0.05) by the increase in the dietary methionine+cystine levels.Consistently with this result, Knowles et al. (1998) andPena et al. (2008) also found no influence of dietary sulfur amino acids in the feed efficiency for weight gain of finishing barrows from 77 to 144 kg and 84 to 109 kg, respectively.
By contrast, assessing methionine+cystine levels in diets for finishing pigs, Santos et al. (2007) found that the feed conversion improved up to the estimated level of 0.506%.The inconsistency among results regarding to weight gain and feed conversion may be related to differences in the genetic potential of pigs for growth.
According to Thong and Liebert (2004), the difference in the genetic potential for weight gain is one of the major factors that influence the requirements of amino acids by the pigs.
There were no effects (P>0.05) of the dietary methionine+cystine levels in the carcass weight, meat amount, backfat thickness at P 2 , and daily meat deposition (Table 3).These results were similar to those described by Loughmiller et al. (1998), Grandhi andNyacothi (2002), andPena et al. (2008), who also did not find significant variation in the carcass traits by increasing the levels of dietary digestible methionine+cystine in studies with finishing pigs.
Likewise, when evaluating different total methionine+ cystine:lysine ratios (50.0, 55.0, 60.0, 65.0, and 70.0%) in diets with 0.55 or 0.65% lysine for male pigs with 60 to 95 kg, Knowles et al. (1998)  Table 2 -Performance and intake of digestible methionine+cystine of 95 to 125 kg castrated male pigs, according to the digestible methionine+cystine in the diets used, confirming that for castrated male pigs, the methionine+cystine:lysine ratio for better carcass traits do not differ between the finishing (60 to 95 kg) and late finishing (95 to 125 kg) phases.Nevertheless, Knowles et al. (1998), in a study with finishing female pigs (74 to 110 kg), found significant variation in the percentage of fat free meat in the carcass by increasing the concentration of methionine+cystine in the diet when assessing levels of these amino acids which corresponded to the ratios of 35 and 65% with lysine.
Sex of the animals and the levels of amino acids assessed are among the factors that may have contributed for the differences observed among studies, because according to Peisker (1982), cited by Thong and Liebert (2004), when weight variation between sexes is the same, females have 13.5% higher protein accretion than castrated males due to the lack of sexual hormones in these animals, resulting in lower capacity of this category to incorporate the amino acids in muscular tissues (Xue et al., 1997).
The results of carcass traits found in this study are consistent with those of performance and show that the digestible methionine+cystine level of 0.427% in the diet, corresponding to a ratio of 57.0 with the digestible lysine met the requirement of late finishing castrated male pigs.

Conclusion
The greatest performance and carcass traits of 95 to 125 kg castrated male pigs with high genetic potential for meat deposition is obtained at 0.427% of digestible methionine+cystine, corresponding to a ratio of 57.0% with the digestible lysine.v.5, p.21-28, 1997.

Table 1 -
Proximate composition and nutritional values of experimental diets also observed no effect of these amino acids levels in the carcass traits irrespective of lysine level 1 Linear effect (P<0.01).