A note on partial replacement of maize with rice bran in the pig diet on meat and backfat fatty acids

The effect of partial substitution of maize with rice bran (maize/rice bran, 62/38, w/w) on feed intake per animal, weight gain per animal at growing-finishing period (kg), feed conversion ratio, weight at slaughter (kg) and fatty acid composition of pork leg and backfat has been studied. The use of diets with maize and rice bran (M/RB) increased (P<0.05) the feed conversion ratio to 3.17 while a value of 3.02 was obtained when maize diets (M) were used. Weights at slaughter were 107.5 and 119.9 kg in animal feed with M/RB and M, respectively. The fatty acid composition of backfat and pork leg was modified by the use of rice bran. In general, tissues from animals fed with M/RB diets showed higher concentrations (P<0.05) of C18:2n-6, C18:3n-3 and polyunsaturated fatty acids (PUFA) (n-6 and n-3) than that found in M diet.


INTRODUCTION
Rice bran is a low price by-product of rice which use allows reducing the final cost of pig rations.Research work published so far with this by-product shows that it is possible to use about 40% of defatted rice bran in swine feeds without affecting negatively both animal performance and carcass quality (Borin et al., 1988).
It has been widely described that fatty acid composition of pork muscle and adipose tissue lipids is mainly influenced by fat diet (Wiseman and Agunbiade, 1998;Kouba and Mourot, 1999;Hoz et al., 2003).For this reason it could be possible that the dietary inclusion of rice bran could modify the fatty acid composition of pork.
The objective of this work was to evaluate the effect of partial replacement of maize with rice bran in pig diets on some growth characteristics and on fatty acid composition of pork leg and backfat at the growing-finishing period.

Experimental design
Twenty castrated crossed male pigs (MS 60 male based on Duroc, Large White and Pietrain × female F1 based on Large White and Landrace) (Fávero, 2000) with approximately 25 kg BW were randomly distributed and located in individual cages and fed a conventional pig diet until they weighed around 40 kg.Ten pigs were randomly assigned to each experimental diet.All pigs were fed ad libitum for 80 days and then weighed.Feed intake of each group of animals and animal weighed before slaughter were recorded.
Ingredients, chemical composition and fatty acids of experimental diets are shown in Table 1.Determination of feed composition was carried out according to AOAC (1995).

Slaughter, sample collection and chemical analysis
Animals were stunned, slaughtered and exsanguinated at a local slaughterhouse at Concordia, Santa Catarina State (Brazil).At 24 h post-mortem, pork from the whole forelegs of the left side of the carcass and the backfat were removed, immediately vacuum packed in low-oxygen permeable film and, kept at -22°C until analysis.Protein (Kjeldhal nitrogen), moisture (oven air-drying method) and ash (muffle furnace) were analysed following AOAC (1995) procedures.Fatty acid analysis was carried out in duplicate within three weeks after slaughter.For lipid analysis, the method of Hanson and Olley (1963) (lipid extraction), Hartman and Lago (1973) (methylation) and Firestone (1998) (analysis of fatty acid methyl esters) were used.Fatty acids were analysed using 0.5 µl of sample in a Konik mod.HRGC 4000 gas chromatograph (Barcelona, Spain) equipped with a flame ionization detector and a capillary column CP Sil 88 Tailor Made FAME (Chrompak).The chromatographic conditions were as follows: the initial column temperature was 180°C, which was kept for 2 min, then raised to 225 at 3.0°C/min and finally held for 15 min; injector and detector temperature was 270°C.Helium was used as carrier gas, at a flow rate of 2 ml/min.Fatty acid methyl esters were identified by comparison with commercial standards analysed in the same conditions and quantified as percentage of total methyl esters.

Statistical analysis
The statistical analysis was performed using the multiple correspondence analysis, and the t-test from the Statistical Analysis System (SAS/1999(SAS/ -2001)).

RESULTS AND DISCUSSION
Feed intake, weight gain per animal, feed conversion and weight at slaughter of animals fed with diets containing maize and rice bran (M/RB) or maize (M) are shown in Table 2.The use of rice brain reduced (P<0.05) the feed intake per animal (kg) from 236.2 (M) to 214.4 (M/RB), the weight gain per animal at growingfinishing period (kg) from 78.2 (M) to 67.7 (M/RB) and the weight at slaughter from 119.9 (M) to 107.5 (M/RB).All these reductions gave raise to a slightly increase (P<0.05) of the feed conversion ratio (3.17 vs 3.02) in the M/RB diet which is in agreement with previous results from Campos (2002).This fact is probably due to a lower digestibility coefficient of rice bran when compare to maize (Rostagno et al., 2000) for protein (74.44 vs 81.5), fat (80 vs 90), crude fibre (39.72 vs 41.42) and digestible organic matter (58.1 vs 76.4).In conclusion, animals fed on M/RB diet had lower feed intake, lower intake of total dry matter, higher intake of crude fat and similar crude protein ingestion.
No effect of dietary treatment was observed in pH at 24 h, water, protein, and ash content (g/100 g wet matter) in pork leg and backfat (Table 3).Only a higher amount of fat (P<0.05) was found in backfat of animals fed with M/RB diet while no differences for fat (P>0.05) were found in pork leg (Table 3).The effect of M/RB and M diet on fatty acid composition of pork legs and backfat are shown in Table 3.The partial replacement of maize with rice bran (diet M/RB) increased the content of total polyunsaturated fatty acids (PUFA) in both pork leg and backfat.The concentration of C18:2n-6, the main n-6 fatty acid, and therefore, the total n-6 fatty acids were significantly higher (P<0.05) in both tissues of animals fed with M/RB diet.Also, the use of the M/RB diet produced an increase (P<0.05) in the C18:3n-3 and total n-3 fatty acid concentration.The fatty acid composition of pork backfat (Table 3) also showed significant differences (P<0.05) for the saturated fatty acids, C14:0, C16:0, C17:0 and C22:0.In general, the results concerning n-3 and n-6 fatty acids were seen as expected because the M/RB diet (Table 1) is richer in C18:2n-6 and C18:3n-3 and, as we previously stated, fatty acid composition in backfat and muscle reflects fatty acid composition in the diet.
The higher variation on the fatty acid composition of backfat is in agreement with the results of Kouba andMourot (1999), Warnants et al. (1999) and Enser et al. (2000) who stated that diets have a weaker influence on muscular fat than on adipose tissue.
The n-6/n-3 ratio in pork foreleg and backfat was not modified by dietary inclusion of rice bran.In both diets, this ratio was higher than the value recommended by the British Nutrition Foundation (1992) in the human diet.Therefore, it should be made an effort to decrease the n-6/n-3 ratio to values closer to the nutritional recommendations in order to improve the nutritional quality of this meat.

CONCLUSIONS
The results for weight gain, feed intake and conversion and fatty acid composition of pork foreleg and backfat prove that maize could be partially substituted by rice bran in pig diet at growing-finishing period, although a slightly higher feed conversion ratio was observed when diets with rice bran were used.

Table 2 .
Feed intake per animal (kg), weight gain per animal (kg), feed conversion ratio at growingfinishing period (80 days) and weight at slaughter (kg) of animals fed diets containing maize and

Table 3 .
Chemical composition (g/100g wet matter), pH and fatty acids (% of total methyl esters) of pork forelegs and backfat of animals fed diets containing maize and rice bran (62/38, w/w) or maize