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METABOLISM AND NUTRITION |
* Centro Interdisciplinar em Investigação em Sanidade Animal–Faculdade de Medicina Veterinária, Pólo Universitário do Alto da Ajuda, Avenida da Universidade Técnica, 1300-477 Lisboa, Portugal; Fertiprado, Herdade dos Esquerdos, 7450-250 Vaiamonte, Portugal; Centro de Ciência Animal e Veterinária–Universidade de Trás-os-Montes e Alto Douro, Apartado 1013, 5000-911 Vila Real, Portugal; Estação Zootécnica Nacional, Instituto Nacional de Investigação Agrária e das Pescas, Fonte Boa, 2005-048 Vale de Santarém, Portugal; and # Instituto Superior de Agronomia, Tapada da Ajuda, 1349-017 Lisboa, Portugal
1 Corresponding author: cafontes{at}fmv.utl.pt
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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-linolenic acid (ALA) and other bioactive compounds. In this study, we evaluated the effects of restricting the intake of a cereal-based feed on the consumption of a legume-based pasture, and consequently on poultry performance and meat quality. Broilers of the RedBro Cou Nu x RedBro M genotype were fed a cereal-based feed at different intake restriction levels (100, 75, or 50% of ad libitum intake) in portable floorless pens located on a subterranean clover (Trifolium subterraneum) pasture. Control birds were maintained at the same site in identical pens but had no access to pasture. The results revealed that, although the growth rate achieved was below the levels expected for the genotype, restriction of cereal-based feed intake had a significant impact on broiler weight gain and feed conversion while leading to an increase in relative leguminous pasture intake (from 1.6 to 4.9% of the total intake, on a DM basis). In addition, bird performance was positively influenced by pasture consumption. The capacity of ingested pasture to modulate carcass characteristics, broiler meat fatty acid profiles, and the meat content of total cholesterol, tocopherols, and to-cotrienols was investigated in broiler chickens slaughtered on d 64. Pasture intake decreased carcass yield (P < 0.05) and meat pH (P < 0.001) and improved breast skin pigmentation (P < 0.001). Consumption of the leguminous pasture had a marginal effect in the vitamin E profiles and cholesterol contents of broiler meat (P < 0.05), although it significantly affected the meat fatty acid profile. Although pasture intake did not influence the linoleic acid content of poultry meat, the levels of n-3 polyunsaturated fatty acids in breast meat [ALA (P < 0.001), eicosapentaenoic acid (P < 0.001), docosapentaenoic acid (P < 0.001), and docosahexaenoic acid (P < 0.001)] were significantly greater in birds consuming the leguminous biomass. Overall, the data suggest an important deposition of ALA and some conversion of ALA to its derivatives in pastured broilers subjected to a restriction of cereal-based feed.
Key Words: feed restriction • pasture intake • broiler performance • fatty acid profile
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Pasture may constitute a source of energy and protein for broilers raised in free-range systems. In addition, the presence of a large range of bioactive compounds in the forage, such as xanthophylls and several hypocholesterolemic and anticarcinogenic compounds, may lead to improvements in meat quality (Ponte et al., 2004). Green forages are also a good source of tocopherols and tocotrienols, the natural diterpenes with vitamin E activity, which are the primary lipid-soluble antioxidants in biological systems (Kerry et al., 2000). Tocotrienols are also known to help lower plasma cholesterol levels (Qureshi et al., 1997). Antioxidant supplementation of feed is an efficient method for increasing meat oxidative stability (Maraschiello et al., 1999), although the various vitamin E forms are known to present different antioxidant potencies (Bourgeois, 1992). However, the contribution of green-pasture vitamin E homologs for the oxidative stability of meat from chicken subjected to dietary restriction remains to be established. Finally, meat provides from one-third to one-half of the daily recommended cholesterol intake (300 mg; World Health Organization, 2003), which seems to be directly associated with a greater risk of hypercholesterolemia (Chizzolini et al., 1999). It was shown previously that the inclusion of leguminous forages in broiler diets contributes to decreased cholesterol content of broiler meat (Ponte et al., 2004). However, recently no changes were observed in cholesterol levels of broiler meat obtained when fresh forages (Ponte et al., 2008a) or dehydrated forages (Ponte et al., 2008b) were included in cereal-based diets for broiler chickens of both slow- and fast growing genotypes.
Poultry meat has been considered one of the main sources of PUFA, particularly n-3 PUFA, for human diets (Howe et al., 2006; Sioen et al., 2006). It has been shown that the content of n-3 fatty acids, particularly -linolenic acid (ALA), in poultry meat can be readily improved by increasing the levels of n-3 PUFA in poultry diets by incorporating linseed oil (López-Ferrer et al., 1999, 2001b), oily fish by-products (Hulan et al., 1988; López-Ferrer et al., 2001a), or both. However, a decrease in flavor quality has been reported for these products because of an overall greater meat susceptibility to lipid oxidation (Manilla and Husvéth, 1999; Bou et al., 2001). It is well known that green pastures are a good source of ALA and that in ruminants, pasture consumption leads to greater contents of this fatty acid in meat while decreasing the n-6:n-3 fatty acid ratio (Wood and Enser, 1997; O’Sullivan et al., 2004). In a recent work developed in our laboratory, we showed that pasture intake promoted the consumption of a cereal-based feed available for ad libitum consumption by free-range broilers, leading to an increased final BW of broiler chicks of a slow-growing genotype (Ponte et al., 2008c). Although the levels of pasture intake were low, ranging from 2.5 to 4.5% of the total DM consumed, the effects on the fatty acid profile of broiler breast meat, while marginal, were significant and resulted in an increased EPA content. In addition, lower levels of the n-3 precursor ALA were observed in meat from these birds, suggesting a greater conversion of ALA into EPA in birds consuming fresh forages (Ponte et al., 2008a). In addition, broilers of a fast-growing genotype grown under a conventional intensive system, fed a diet containing 11% of a dehydrated legume-based forage and slaughtered on d 28, had meat with an improved fatty acid profile containing greater levels of n-3 LC PUFA [C 
20, i.e., EPA, docosapentaenoic acid (22:5n-3; DPA), and DHA; Ponte et al., 2008b]. More recently, a study by Horsted and colleagues (2007), using laying hens fed organic diets with access to pasture, suggested that restricting the intake of a cereal-based feed promoted foraging and therefore consumption of the fresh forage. The objective of the research reported here was to establish the effect of restricting the intake of a cereal-based feed on the consumption of a legume-based forage by free-range-pastured broilers of a slow-growing genotype. In addition, the implications of pasture intake on bird performance and the resulting meat content of cholesterol, fatty acids, vitamin E homologs, and β-carotene were evaluated.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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This experiment was performed in the autumn of 2004 at Herdade dos Esquerdos (039°07.18' N, 007° 29.36' W, 318 m above sea level), Vaiamonte, Portugal. During the experiment, the average daily mean temperature was 9.5°C (the mean of the highest temperatures was 17.2°C and that of the minimum was 4.4°C) with 7 d with rain and a total precipitation of 27 mm. Two hundred forty 36-d-old males RedBro Cou Nu x RedBro M, vaccinated against Marek’s disease, were divided into 24 floorless portable metal outdoor pens (10 birds per pen), with both the mean and the variance of BW equalized. Before commencing the experiment, birds were maintained in a conventional indoor facility following standard brooding procedures and were fed a typical corn (Zea mays) and soybean meal diet. Birds were maintained in the pastured pens described below for an additional 28 d until slaughtered on d 64. The movable pens (1.7 x 1.5 x 0.5 m; 0.255 m2 per bird) allowed birds direct contact with the legume-based pastures. Approximately one-third of the top of each cage area was covered with transparent whitewashed plastic for protection against harsh climatic conditions. Water was available for ad libitum consumption throughout the experiments and was provided via 2 automatic drinking nipples. A cereal-based feed was provided in one individual hanging tube feeder per pen. The composition of the cereal-based feed used in these studies, which was formulated to contain adequate nutrient levels as defined by the NRC (1994), is presented in Table 1
. The birds were randomly assigned to 1 of the 6 treatments, with 4 replicates of 10 birds per treatment. The 6 treatments consisted of 3 levels of cereal-based feed consisting of 100% (100), 75% (75), or 50% (50) of the reference intake to the breed and age (http:// www.hubbard-isa.com), and 2 levels of pasture access, without access to pasture (no pasture) or with access to a Trifolium subterraneum-based pasture (pasture), in a completely randomized experimental design. To promote forage intake, the portable pens of the treatments with access to pasture were moved daily so that birds could consume fresh herbage every day. Pens in the no-pasture treatment were located in a fixed position in the same field, and access to the pasture was blocked in the initial days and throughout the experiment by adding new pine wood shavings to the ground. On d 50, samples of the pasture were collected from 1 m2 paddocks by cutting it at 3 cm above the ground, for chemical evaluation. The experimental protocol was approved by the ethics commission of Centro Interdisciplinar em Investigação em Sanidade Animal (CIISA) following the appropriate European Union guidelines (No. 86/609/EEC).
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Skin Color
The color of breast skin was evaluated by using a Minolta Chroma Meter CR-300 (Konica Minolta Sensing Americas Inc., Ramsey, NJ ). The readings were taken on equivalent positions of the carcasses. The tip of the chromameter measuring head was placed flat against the surface of the skin. For each reading, 3 measurements were performed, and the final value for each bird is the average of those readings. Skin color was expressed in the CIELAB dimensions of lightness (L*), redness (a*), and yellowness (b*).
Determination of Total Lipids
Meat samples were lyophilized (–60°C and 2.0 kPa) to a constant weight by using an Edwards Modulyo lyophilizer (Edwards High Vacuum International, Norfolk, UK), maintained desiccated at room temperature, and analyzed within 2 wk. For determination of total lipids, intramuscular fat was extracted from the lyophilized samples (0.25 g) as described by Alfaia et al. (2006). Total lipids were measured gravimetrically, in duplicate, by weighing the fatty residue obtained after solvent evaporation.
Determination of Fatty Acid Composition
Intramuscular fat of lyophilized samples (0.25 g), cereal-based feed, or pasture (0.10 g of DM) was first dissolved in 1 mL of dry toluene. Fatty acids were then converted to methyl esters (FAME) by base-catalyzed transesterification with sodium methoxide for 2 h at 30°C. The fatty acid composition was determined by gas chromatography of FAME, performed with a Varian 3800 gas chromatograph (Varian Inc., Walnut Creek, CA) equipped with a flame-ionization detector and an OmegaWax 250 (Supelco, Bellefonte, PA) capillary column (30 m x 0.25 mm i.d., 0.25-µm film thickness). The chromatographic conditions were as follows: injector temperature, 250°C; detector temperature, 280°C; helium was used as carrier gas; and the split ratio was 1:20. The gas chromatograph oven temperature was programmed to start at 150°C (maintained for 15 min), followed by a 3°C/min increase to 220°C (maintained for 20 min). Identification was accomplished by comparing the retention times of peaks from samples with those of FAME standard mixtures. Quantification of FAME was based on the internal standard technique, with nonadecanoic acid (19:0) as the internal standard (Nu-Chek Prep. Inc., Elysian, MN), and on the conversion of relative peak areas to weight percentage by using the corrected response factor of each fatty acid (ES ISO 5508; European Committee for Standardization, 1990). Fatty acids were expressed as gravimetric contents (mg/g of muscle) or as a percentage of the sum of identified fatty acids (% wt/wt).
Quantification of Total Cholesterol, Tocopherols, and Tocotrienols
The simultaneous determination of total cholesterol, β-carotene, tocopherols, and tocotrienols was performed as described by Prates et al. (2006). The method involves a direct saponification of the fresh meat (0.75 g), cereal-based feed, or pasture (0.10 g of DM); a single n-hexane extraction; and analysis of the extracted compounds by normal-phase HPLC by using fluorescence detection (tocopherols and tocotrienols) and ultraviolet-visible photodiode array detection (cholesterol and β-carotene) in tandem. Briefly, the analyses were performed by using a normal-phase silica column (Zorbax RX-Sil with the corresponding 12.5-mm analytical guard column, 250 mm length x 4.6 mm i.d., 5-µm particle size; Agilent Technologies Inc., Palo Alto, CA), with fluorescence detection for tocopherols (excitation wavelength of 295 nm and emission wavelength of 325 nm) and ultraviolet-visible photodiode array detection for cholesterol (202 nm) and β-carotene (450 nm) in series. The solvent [1% (vol/vol) isopropanol in n-hexane] flow rate was 1 mL/min, the run lasted for 17 min, and the temperature of the column oven was adjusted to +20°C. The injection volumes used varied between 20 and 100 µL to obtain values within the linearity range of the standard curves. The content of total cholesterol, β-carotene, tocopherols, and tocotrienols was calculated in duplicate for each sample, based on the external standard technique, from a standard curve of the peak area versus the compound concentration.
Statistical Analysis
Statistical analysis (ANOVA) was conducted by using the GLM procedure of SAS (SAS Institute, 2004). The model used to analyze data from the pasture experiment included the effect of pasture intake (P), the effect of cereal-based feed restriction (R), and the interaction between P and R (P x R). The experimental unit considered was the pen. The significance levels for the main effects of pasture, restriction, and the interaction between these 2 effects are presented. Orthogonal contrasts were constructed to test differences between restriction levels. The first contrast (100 vs. 75) compared the parameters from birds with no restriction (100) with birds subjected to 75% of the referenced intake (75). The second contrast (75 vs. 50) compared the parameters from birds with 75% restriction (75) with birds with access to 50% of their referenced intake (50). Unless otherwise stated, differences were considered significant when P < 0.05.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Total fatty acids were greater in the cereal-based feed than in the pasture (Table 2). As expected, linoleic acid (LA; 18:2n-6) was the major fatty acid in the cereal-based diet, whereas ALA predominated in the legume-based pasture. Palmitic acid (16:0) was relatively abundant in both feeds. The cereal-based feed contained greater percentages of oleic acid (18:1n-9) when compared with the pasture. In addition, EPA (20:5n-3) and DHA (22:6n-3) were present at very low levels (data not shown). The ratio of LA to ALA was 0.15 and 16.7 in pasture and in cereal-based feed, respectively.
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-tocopherol was coeluted with a minor proportion of β-tocotrienol, a profile of vitamin E compounds was obtained (Table 2
). The - and -tocopherols were the most abundant vitamin E homologs in both the cereal-based diet and the legume-based pasture. In addition, compared with cereal-based feed, the pasture biomass had significant levels of β-carotene. Pasture Intake and Bird Performance
Although pasture consumption was low, cereal-based feed restriction resulted in a significantly greater (P < 0.05) proportion of pasture intake in the total intake (Table 3). The legume-based pasture was estimated to constitute 1.6, 2.8, and 4.9% (DM basis) of the total intake in birds consuming the cereal-based feed at 100, 75, and 50% of the reference intake, respectively. Analogous results were obtained in a study with organic laying hens (Horsted et al., 2007). In addition, the recorded percentages of forage intake in this study were lower than those reported by Ponte et al. (2008a) in experiments with an ad libitum supply of cereal-based feed. However, these values should be viewed with some caution, because they represent an estimate of the pasture consumption at a specific moment of the trial, and forage consumption may have varied during the experiment. Climatic factors and time of day are known to have important effects on the range area used and forage consumption of laying hens (Hegelund et al., 2005; Horsted et al., 2007). Interestingly, although the proportion of pasture intake increased with the level of restriction, the absolute pasture consumption was equivalent in all groups. Total pasture intake, estimated according to cereal-based feed intake, varied between 400 and 474 g (DM basis) during the 28 d of the experiment. The mortality rate during this experiment was moderate (5.6%) and was not related to the treatments (data not shown).
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). Birds in treatments 75 and 50 displayed lower weight gains and BW compared with birds from the nonrestricted groups. Although no significant difference was observed in weight gain as a result of restricting the cereal-based feed intake in the last week of the experiment (P > 0.05), total weight gain and final BW were significantly decreased in birds in the cereal-based feed-restricted groups (P < 0.001). Other researchers have also observed that limiting feed intake depresses growth during the period of restriction (Acar et al., 1995; Govaerts et al., 2000). Birds subjected to the most severe feed restriction were unable to compensate for the reduced performance resulting from the reduced cereal-based feed intake by increasing pasture intake; therefore, a significant decrease in growth rate was observed. As expected, the data suggest that the high fiber content of pasture biomass limited the feed intake and nutrient utilization of the birds. Nevertheless, although no differences were observed between the weight gain and BW of birds consuming or not consuming pasture throughout the trial, a cumulative effect was observed that allowed the total weight gain (P < 0.01), and consequently the final BW (P = 0.075), to be greater in grazing birds.
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Meat Physical Properties
Both restriction of feed intake and pasture consumption had a negative effect on carcass yield (P < 0.001 and P < 0.05, respectively; Table 5). In addition, a significant interaction between pasture intake and feed intake restriction (P < 0.01) resulted in a greater decrease in carcass yield in birds consuming pasture compared with birds without access to pasture that were subjected to the feed intake restriction. It is widely accepted that dietary fiber can influence the development and size of the digestive organs in broilers chicks (Brenes et al., 1993; Mourão et al. 2007), which in turn has a significant influence on carcass yield. It is also known that birds with lower live weights attributable to a lower intake of nutrients, like the ones subjected to the feed restriction, usually have a lower carcass yield (Havenstein et al. 2003). In addition, the greater activity of grazing birds in conjunction with the imposed feed restriction might have improved the proportion of wings, thighs, and drumsticks (Castellini et al., 2002). In contrast, Fanatico et al. (2005) found no differences in the carcass yield of indoor and outdoor birds, and Ponte et al. (2008a) observed increases in carcass yields in pastured broilers. In addition, decreases in carcass yields in birds with access to pasture suggest that foraging could increase the proportion of gastrointestinal tract tissues in the overall BW as an adaptation to a greater fiber intake. Meat pH was lower in breast originating from grazing birds (P < 0.001). This result may reflect the different management conditions of pasture birds that are allowed to graze, thereby allowing more activity (Castellini et al., 2002; Fanatico et al., 2007). The significant interaction between the effect of feed restriction and pasture intake (P < 0.05) resulted in a greater decrease in meat pH in birds consuming pasture, compared with birds without access to pasture that were subjected to feed restriction.
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). Interestingly, feed restriction induced a considerable decrease (P < 0.01) in broiler carcass redness (a*), showing that the usually undesirable pink and red tones in the skin were less developed. Pasture intake did not influence broiler skin L* and a* values (P > 0.05). Breast skin yellowness (b*) was influenced by feed restriction (P < 0.05), pasture intake (P < 0.001), and the interaction between this 2 effects (P < 0.001). In birds consuming legume-based pasture, feed restriction had the opposite effect, inducing a large increase in breast skin yellow tones, most probably supplied by the natural pigments present in the legume-based pasture. Nevertheless, no differences were observed in the breast skin b* scores between birds without feed restriction resulting from pasture consumption. This is supported by the observation that although pasture contains carotenoid pigments (Toyopmizu et al., 2001; Table 2), there was no improvement in breast skin yellowness when diets contained a considerable proportion of corn (Schaible, 1970). Fatty Acid Composition and Cholesterol, Tocopherol, and Tocotrienol Content of the Meat
The predominant fatty acids in meat from birds of all treatments were palmitic (16:0) and stearic (18:0) acids as saturated fatty acids, oleic acid as a monounsaturated fatty acid, and LA and arachidonic acid (20:4n-6) as PUFA (Table 6). Oleic and palmitic acids were the most abundant fatty acids in the various meats under analysis. The restriction on intake of the cereal-based feed induced several changes in the fatty acid profile of broiler meat. The percentages of 18:1n-9 and 22:2n-6 fatty acids were lower in the meat from birds receiving only the cereal-based feed at 75 or 50% of the reference intake. However, the restriction on cereal-based intake had an opposite effect on the levels of 17:0, 18:0, 20:1n-9, 20:4n-6, 20:5n-3, 22:5n-3, and 22:6n-3. Together, the data suggest that the significant increase in stearic acid and decrease in oleic acid resulted from a depression in the activity of stearoyl-CoA desaturase in birds of the forage-consuming group. It is well known that stearoyl-CoA desaturase expression can be regulated by nutritional factors (Rosebrough et al., 2005). In addition, pasture consumption influenced the fatty acid profile of broiler meats, leading to significant increases in most PUFA. Although no changes were observed in the contents of LA and 18:3n-6 in meat from birds with access to pasture, all the other n-6 PUFA levels were enhanced (P < 0.05). However, a significant effect of pasture intake in fatty acid content was observed for all the n-3 PUFA percentages (P < 0.001). The level of ALA was influenced by pasture intake (P < 0.001). However, the ALA content was affected differently by pasture intake analyzed in birds subjected to the different restriction levels (P < 0.001). In birds without access to pasture, feed restriction resulted in lower ALA contents in the meat. In contrast, in birds consuming the legume-based pasture, feed intake restriction had the opposite effect, inducing a large deposition of the main n-3 PUFA in breast meat. The n-3 PUFA were most possibly supplied by the legume-based pasture, in which ALA was the most abundant fatty acid. Levels of n-3 LC PUFA [EPA, DPA, and DHA (P < 0.001)] were greater in birds consuming pasture. Nevertheless, because n-3 LC PUFA were present in trace levels in both the cereal-based feed and in pasture, these data suggest a significant conversion of ALA, by desaturation and elongation, to its derivatives in broilers with access to pasture. Similar results have been obtained in previous studies in birds consuming linseed oil (López-Ferrer et al., 2001a) and leguminous biomass (Mourão et al., 2007; Ponte et al., 2008b,c). This finding supports the view that chickens have the ability to deposit ALA in muscle tissues and convert this fatty acid to its derivatives. However, the levels of ALA, EPA, DPA (22:5n-3), and DHA in the broiler meat of pasture-consuming birds were much lower than the percentages of n-3 fatty acids reported in meat originating from birds supplemented with 2 to 4% of fish oil (López-Ferrer et al., 2001a). This may be explained, at least in part, by the fact that the ALA present in the pasture was in the esterified form in structural lipids, including galactolipids from chloroplasts (Gurr, 1984). Thus, the broiler digestive system may not have been able to generate free ALA via hydrolysis of galactolipids because of a lack of galactolipase activity.
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, the restriction in cereal-based feed intake contributed to an increase in the total PUFA, n-3 PUFA, and n-6 PUFA content of broiler meat (P < 0.001), induced by a decrease in the content of monounsaturated fatty acids, particularly oleic acid (Table 7). Although pasture consumption did not result in significant changes in total n-6 PUFA, n-3 PUFA percentages were improved (P < 0.001). Consequently, the n-6:n-3 ratio in meat derived from grazing birds was lower than that in birds exclusively consuming the cereal-based feed. Interestingly, the effect of pasture intake was evident even in birds consuming the cereal-based feed at the level of 100% of the reference intake. This observation is surprising because it contradicts previous observations suggesting that at a nonrestricted level of intake of cereal-based feed, pasture intake has no effect on the n-6:n-3 ratios of broiler breast meat (Ponte et al., 2008b). Reference intakes stated in the breed standards consider typical housing facilities. However, it is well known that free-range production systems are usually associated with greater feed intakes, which allow birds to counteract harsh weather conditions. Therefore, it is likely that in the present experiment, birds in the 100% intake treatment could have been subjected to a slightly restricted consumption, which could have increased pasture intake. This is supported by the observation that pasture intake (Table 3) was remarkably similar across the 3 restriction treatments in birds in the grazing treatments. Taken together, the data suggest that when free-range broilers are given free access to high-quality pastures and subjected to a minor intake restriction of the cereal-based feed, this might be sufficient to improve the n-3 fatty acid content of the broiler meat.
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). However, all chicken meats were lean, based on the Food Advisory Committee (1990) criteria (<5% fat), and depicted median contents of total cholesterol (0.42 to 0.46 mg/g) compared with those reviewed by Chizzolini et al. (1999) for beef. Meat total cholesterol concentration was increased in meat from birds subjected to the greatest feed restriction (P < 0.05) and in birds with access to pasture (P < 0.05). However, the increase in meat cholesterol concentration, as influenced by the level of feed restriction, was exclusive to the birds without access to pasture (P < 0.05).
The diterpenes -tocopherol and -tocotrienol were the major vitamin E homologs detected in broiler breast meat (Table 8). In addition, breast meat presented trace levels of -tocotrienol, β-tocopherol, and -tocopherol (the latter coeluted with a minor proportion of β-tocotrienol). The prevalence of -tocopherol in meat is well established and results from the more than 10-fold preference of the tocopherol-binding protein for -tocopherol in relation to the -homologs, which are the most common vitamin E molecules in plant foods (Decker et al., 2000). Restriction of cereal-based feed intake had no effect on diterpene deposition in broiler meat. Meat from birds with access to the legume-based pasture presented lower levels of -tocopherol (P < 0.01), β-tocopherol (P < 0.05), and -tocopherol (P < 0.01; Table 8). This was not completely unexpected because the cereal-based feed displayed greater concentrations of these vitamin E homologs (Table 2). In addition, although the legume-based forage had significant levels of β-carotene, pasture intake had no influence on the levels of this lipid-soluble antioxidant provitamin in breast meat.
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ACKNOWLEDGMENTS |
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Received for publication December 21, 2007. Accepted for publication June 3, 2008.
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