PERFORMANCE AND QUANTITATIVE AND QUALITATIVE CARCASS TRAITS IN PIGS

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INTRODUCTION
Brazil is the fourth world producer and exporter of pigs and, in 2010, per capita pig consumption was 14.8 kg (ABIPECS, 2011).Soybean meal (Glycine max) is the most used protein source to formulate diets for pigs (CROMWELL, 2010).However, due to its high cost, it is necessary to evaluate other protein sources, such as canola (Brassica napus), cotton (Gossypium herbaceum), sunflower (Helianthus annuus), and peanut (Arachis hypogaea).
Canola is a rapeseed cultivar (Brassica napus) that contains low levels of glucosinolates in the seed (<3 μg g -1 ) and erucic acid in the oil (<2%) (Bell, 1993).In Brazil, its cultivation has been increasing as an option for the winter harvest and the production of oil rich in unsaturated fatty acids (SANTOS; BASSO, 1990).
Canola meal (CM) is a by-product of oil extraction and has a great content of sulphur amino acids, ether extract, fibres, calcium, phosphorus (Keith & Bell, 1991), and vitamins of the B complex (niacin, thiamine, riboflavin, folic acid, and biotin), compared with soybean meal (BELL, 1993).However, it has limiting factors, such as the production of metabolites of glucosinolates, trypsin inhibitors, phytic acid, phenolic compounds, and tannins (TESKEREDZIC et al., 1995).
The goal of the present study was to assess the nutritional value of CM in diets for growingfinishing pigs and its effects on performance and carcass traits.

MATERIAL AND METHODS
The experiments were carried out in the swine sector of Iguatemi Experimental Farm, Agricultural Sciences Centre of the State University of Maringá, State of Paraná, Brazil (23°21' S, 52°04' W; 564 m altitude).
Were conducted two experiments.The first assessed the total digestibility of CM and the second assessed the performance of growing-finishing pigs and carcass traits.The CM was acquired in an agroindustrial firm of the State of Paraná, Brazil.The experimental procedures and the use of animals were previously approved by the Ethics Committee of the State University of Maringá, Approval Certificate No. 136/2010.
The digestibility experiment was carried out from March to April 2010 assessing 14 castrated commercial crossbred male pigs with initial live weight of 60.69 ± 4.26 kg.The pigs were housed in individual metabolism crates under controlled environment.The digestibility trial lasted 15 days, ten for adaptation and five for collecting faeces and urine.The control diet consisted of maize (72.97%), soybean meal (24.45%), salt (0.570%), calcium carbonate (0.635%), dicalcium phosphate (0.875%), and mineral-vitamin supplement (0.50%).These components were formulated according to the requirements proposed by Rostango et al. (2005).Were used two diets (treatments): control; and control (75%) with addition of CM (25%) performing seven repetitions per treatment.
Provision of diets and collection of faeces and urine were performed according to the method proposed by Sakomura and Rostagno (2007).During the collection period, feed intake was calculated based on the metabolic weight (kg 0.75 ) of each pig and the average consumption recorded during the adaptation period (approximately seven days).
To set the beginning and the end of the faeces collection procedure, were used 3% iron oxide (Fe 3 O 2 ) as faecal marker (SAKOMURA; ROSTAGNO, 2007) and faeces were collected once a day, packed in plastic bags and stored in a freezer (-18 °C).Subsequently, each sample was homogenized and dried (approximately 350 g) in a forced-ventilation oven (55 °C) and ground in a blade mill (1 mm sieve).Urine was collected in plastic buckets with 20 mL of HCI solution (1:1) to avoid bacterial growth and nutrient losses by volatilization.The analyses of feed and faeces were performed according to the procedures described by Silva and Queiroz (2002).Total energy values were determined by adiabatic calorimetry (Parr Instrument Compant, Illinois, USA).The digestibility coefficients of dry matter (DMDC), energy (EDC), protein (PDC), and organic matter (OMDC) were calculated according to the method proposed by Moreira et al. (1994).
Experiment II assessed the performance during the growing (30-60 kg) and finishing (60 to 90 kg) phases and was carried out from July 2010 to February 2011.During the experiment, the minimum average temperature was 18.8 ± 2.32 °C and the maximum 29.1 ± 4.11 °C.Were used 50 commercial crossbred pigs whose average initial live weight was 29.90 ± 1.16 kg and the average finishing live weight was 60.33 ± 3.38 kg during the growing phase.During the finishing phase, the average initial live weight was 60.37 ± 1.46 and the average final live weight was 90.37 ± 3.19 kg.The pigs were housed in brick sheds divided into two sectors, each with 10 pens (7.60 m 2 each) separated by a central corridor.Each pen had pacifier-type drinkers at the back and single feeders at the front, which provided free access to feed and water.The diets and water were provided ad libitum throughout the experiment.The treatments consisted of four diets (6, 12, 18, and 24% CM) and a control diet (0% CM).The diets (Tables 1  and 2) were formulated as recommended by Rostagno et al. (2005) for growing-finishing pigs.We assessed the ileal digestibility to determine the digestible amino acids of the CM and the results were used to formulate the diets.Were determined the levels of protein, phosphorus, and calcium in maize and soybean meal samples at the Laboratory of Food and Animal Nutrition Analysis, State University of Maringa, Paraná, Brazil.The metabolizable energy values were those cited by Rostagno et al. (2005).The values of digestible amino acids of maize and soybean meal were calculated using true amino acid digestibility coefficients reported by Rostagno et al. (2005).
Table 2. Centesimal and chemical composition of diets containing different levels of canola meal (CM) for finishing pigs feeding (60-90 kg).However, Moreira et al. (1996) worked with growing-finishing pigs and concluded that there was a reduction in the performance of the pigs according to increased CM levels in the diets.These authors linked this behaviour to the fact that CM contains high levels of crude fibre that can impair the performance.Thacker and Newkirk (2005) worked with growing-finishing pigs (28.7 to 107.4 kg of live weight) and observed that there was a reduction in daily weight gain and feed:gain ratio during the growing phase when they completely replaced soybean meal with CM as a protein source.In the finishing phase, total replacement did not affect daily feed intake, daily weight gain, and feed:gain ratio.
On the other hand, Roth-Maier et al. ( 2004) observed an improvement trend in the yield variables of growing animals with increased levels of CM inclusion (0-26%).However, there was a linear decrease in daily gain weight as the CM level increased (0-17%).Gomes et al. (1998) observed that it was possible to include 15% of CM in the diet of finishing pigs, whereas Brand et al. (2001) concluded that the inclusion of 24% for pigs with 25 to 84 kg live weight did not affect the performance.The experiment carried out by Zanotto et al. (2009) showed a detrimental effect on the feed:gain ratio during the growing phase and a limitation in the daily feed intake during the finishing phase when high levels of CD (replacement level above 40% of soybean meal) were included to replace soybean meal.
Results obtained by Seneviratne et al. ( 2010) were similar to those of the present study.They assessed pigs fed on diets containing a maximum of 23% CD during the growing phase and found no differences.However, these authors reported that, when they increased the level of CM inclusion in finishing pigs, the daily weight gain decreased linearly and feed:gain ratio worsened.With regard to the quantitative carcass traits (Table 4), none of the variables was influenced by the addition of CD (p ≥0.05).
Dunnett's test indicated that there was no difference (p ≥0.05) between the levels of CM inclusion and the control diet (0% CM) for most variables.However, for the variables 'hot carcass weight' and 'cold carcass weight', the values were lower (p ≤0.05) between inclusion levels of 12, 18, and 24% for hot carcass weight and between 18 and 24% for cold carcass weight compared with the control diet.This result is due to the lower weight of these animals at sacrifice.However, special attention should be given to these variables.Losses during cooling represent an important value related to the percentage of carcass water loss in the refrigerator (BRIDI; SILVA, 2009).Therefore, these results indicate that up to 24% of CM inclusion in the diets does not affect the quantitative carcass traits in pigs.
The results obtained in the present study are similar to those obtained by Gomes et al. (1998), Roth-Maier et al. (2004), and Thacker and Newkirk (2005), which did not show any effect of the CM level replacing soybean meal on the carcass traits assessed in growing-finishing pigs.Rojo et al. (2001) assessed the potential of partial (50%) or total (100%) replacement of soybean meal with CM and the effects on pigs sacrificed at 100 kg live weight.They reported that carcass yield, meat percentage, and backfat thickness were not affect by the treatments.However, Brand et al. (2001) assessed the carcasses of lightweight pigs (up to 85 kg live weight) including high CM levels.They found a reduction in backfat thickness, increase in the percentage of carcass meat, and reduction in the carcass performance.
In addition, Zanotto et al. (2009) reported that the inclusion of CM in the diet resulted in carcasses with lower meat yield.With the exception of colour (a*), lightness (L*), and tonality (b*) of the longissimus muscle, none of the other qualitative meat traits (Table 5) were influenced by the inclusion of CM (p ≥0.05).
Table 4. Effect of diets with different levels of canola meal inclusion (CM) on quantitative carcass traits of pigs in finishing (60 to 90 kg).† Standard Error; † † CV = Coefficient of variation; § Linear Effect of Levels Canola Meal; ¶ Quadratic Effect of Levels Canola Meal; NS = non-significant; * Significant (p ≤ 0.05) the Dunnett tests.There was a linear decrease (p≤0.05) in lightness (L*) and tonality (b*) of the longissimus muscle as the CM level increased in the diet.Dunnett's test indicated differences (p ≤0.05) between the levels of CM inclusion and the control diet (0% CM) with respect to muscle colour.
With respect to lightness (L*), the inclusion of 18 and 24% of CM exhibited difference (p ≤0.05) with respect to 0% CM.For the variables saturation (a*) and tonality (b*), the inclusion of 24% CM showed differences (p ≤0.05) compared to 0%.Dunnett's test did not show difference (p ≥0.05) in the other qualitative muscle traits.Rojo et al. (2001) reported that high canola levels darkens the meat.However, some authors (HERTZMANN et al., 1988;BELL et al., 1991;NRC, 1998) did not mention this risk when they used turnip paste with high levels of glucosinolates and rich in erucic acid.As a result, the possibilities of generating dark meat with CM would be less.

CONCLUSION
The addition of up to 24% CM did not interfere in the performance and quantitative and qualitative carcass traits in growing-finishing pigs.CM can be used as alternative protein source in the balancing of diets for pigs.However, it is important to conduct further studies to determine whether the cost-benefit ratio is adequate.

Table 5 .
Effect of diets with different levels of canola meal inclusion (CM) on qualitative traits of Longissimus dorsi muscle in pigs (60 to 90 kg).†-Standard error; † †-CV = Coeficiente de variación; §-Linear Effect of Levels CM (Minolta b: Y=6.6145-0.0652583x;Minolta L: Y=57.253-0.218756x);¶-Quadratic Effect of Levels CM; a FLT =Fluid loss from thawing; b FLC = Fluid loss from cooking; ¤-a*: indicates the color of the flesh varies from red to green (green red high color indicates red, low color indicates green); b*: indicates the flesh color varying from yellow to blue (b* high indicates yellow color, b* low indicates blue color); L*: indicates the degree of brightness of the flesh (L* = 0 dark meat, L = 100 white meat); NS = non-significant; *Significant (p ≤ 0.05) the Dunnett tests.

Table 1 .
Centesimal and chemical composition of diets containing different levels of canola meal (CM) growing pigs feeding (30 a 60 kg).

Table 1 .
Centesimal and chemical composition of diets containing different levels of canola meal (CM) for growing pigs feeding (30 a 60 kg).