Qualitative traits of the meat of Nellore steers supplemented with energy and protein in an integrated crop–livestock system

Additional keywords: marbling, shearing force, zebu.

Brazil has the largest commercial herd of cattle in the world, with ~212.8 million heads (IBGE 2012). However, with the growth of the beef industry and beef exports, it is imperative to maximise and modernise this sector, especially the segments of animal production, slaughtering and meat processing.

The development of livestock market makes beef-cattle producers increase their degree of specialisation. Consequently, the number of properties that perform only one specialised area of beef production has increased, developing specific activities of cow–calf operations, stocker production and fattening. In this context, feedlots for fattening steers represent a small fraction of the slaughtered carcasses, which most coming from cattle raised on pasture.

Disregarding the value of the animal, in intensive systems, the most representative cost is concentrate feeds (70–75% of the operational costs), limiting the profitability of the entire production system (Cunha et al. 2012; Lopes et al. 2012b). Integrated crop–livestock systems become interesting due to reduction in costs, environmental benefits and sustainability (Pacheco et al. 2006; Zorzi et al. 2013).

In the Santa Fe model of integrated crop–livestock system, grain crops and grasses are grown intercropped. After crop harvest, the pastures are grazed in the dry season and, after that, accumulate straw for no-till systems. In this way, protein and energy supplementation can contribute to finishing steers on pastures, attending to the increasing demand from internal and external markets for high-quality red meat (Lobato et al. 2014).

Thus, aspects related to qualitative traits of carcass and meat assume an important role for aggregating value to the product. According to Luchiari Filho (2000), the evaluation of carcass yield and meat quality are essential to improve the efficiency of beef-cattle production systems. The quantitative and qualitative traits of carcasses are important, because they are directly related to the final product (Silva et al. 2014). Nevertheless, they help obtain products of superior quality and more competitiveness in the market.

Meat quality is evaluated by structural, physical–chemical and sensorial parameters, in which nutritional value, fat content and fatty acid composition are important factors (McAfee et al. 2010). For Brazilian beef to gain a wider place in the market, it is imperative to focus more attention on meat quality. Several fatty acids are of interest to the meat industry because of their health benefits (Mir et al. 2004). Therefore, the meat industry has looked for means to reduce saturated fatty acids and increase polyunsaturated fatty acids (PUFA). These fatty acids include linoleic and linolenic fatty acids, which are considered beneficial because they belong to omega-6 and omega-3 series respectively, and also conjugated linoleic acid. Hence, an important role of animal production is to provide good-quality meat for human consumption (Madruga et al. 2006).

Polyunsaturated fatty acids have usually been associated with beneficial health effects on early life and later-life disease such as cardiovascular diseases (Khandelwal et al. 2012). The benefits of PUFA in human nutrition are recognised by the Food and Agriculture Organization (FAO 2008) and the European Food Standards Authority (EFSA 2010) guidelines for fat intake and composition, although there are knowledge gaps that need further research (Butler 2014). The aim of the present work was to evaluate the physical and chemical composition of the muscle meat Longissimus dorsi of castrated Nellore steers fed with increasing levels of protein and energy in an integrated crop–livestock system. The hypothesis was that supplementation can improve the main meat-quality traits.

The experiment was conducted at Stone Farm, located in the municipality of Luis Eduardo Magalhaes, west of Bahia (known as grain belt), during the dry season, between July and October 2011. The experiment lasted for 105 days, of which 15 days were for adaptation.

For the experiment, 40 Nellore males, chemically castrated with a commercial product (Bopriva®), aged 33 ± 6.7 months and an initial average bodyweight (BW) of 396 ± 16.1 kg, treated against worms and identified with numbered ear tags, were used. The animals were distributed in a completely randomised design, divided into four groups, with 10 animals in each group. There were eight testers and two tracers, to adjust the forage supply to 10 kg of DM/100 kg of BW.

The animals received increasing levels of concentrate (1.0, 2.0, 3.0, and 4.0 kg/animal.day), which consisted of 17% crude protein and 75% of total digestible nutrients (Tables 1, 2). However, after adjustments by daily intake to allow maximum amounts of orts of 10%, the final concentrate consumptions were 0.98, 1.45, 1.86 and 2.02 kg/animal.day, representing 0.23%, 0.34%, 0.44% and 0.47% of the BW respectively. The previous history (all the life raised on pastures without any concentrate), the genetic of cattle (zebuine) and the high-herbage availability (3892 kg/ha), allowing to select better forage quality, contributed to the reduced concentrate intake.

Table 1.  Chemical composition (g/kg DM) of the ingredients used in the experimental diets and pasture
Neutral (NDF) and acid (ADF) detergent fibre have been corrected for ash and protein

Table 2.  Percentage of ingredients and chemical composition of the concentrate

Concentrate was offered once a day, in the morning (0800 hours), in a 2-m-long feeder, with access from one side.

Pasture consisted of four paddocks of 10.5 ha, 42 ha in total, where corn plus Brachiaria ruziziensis, soybean and cotton were cultivated in rotation, using the Santa Fe model of integrated crop–livestock system. In that year, corn and B. ruziziensis grass were cultivated. After the corn harvest, electric fences, drinking fountains and feeders were installed. The paddocks were deferred for 60 days before the beginning of the trial, aiming to accumulate more forage for the dry season.

The steers were slaughtered at the end of the experiment in a commercial slaughterhouse (FRIBARREIRAS©), in Barreiras, Bahia, Brazil, which is located 120 km from the farm. The hot carcass weight was measured for subsequent evaluation of carcass yield and typification. The Bovine Classification System was regulated by MAPA (Ministry of Agriculture, Livestock and Supply, regulation no. 9 of 4 May 2004). The carcasses of the animals were divided into two half-carcasses, which were weighed and cooled in a cold room at 5°C for 24 h. Then, carcasses were cut longitudinally, at the height of the midline, into two antimeres. The half-carcasses were sectioned between the 12th and 13th ribs to collect the loin (Longissimus dorsi muscle), according to the adaptations of the method of Colomer-Rocher et al. (1987).

The pH was measured by a Mettler M1120x digital potentiometer, equipped with an insertion electrode, with a resolution of 0.01 (Gomide et al. 2006), directly from the Longissimus dorsi muscle at the 12th rib. These values were measured 24 h after slaughter and after the sample was defrosted.

The determination of the loin eye area (LEA) was performed on the surface between the 12th and 13th ribs. Transparent sheet and appropriate pen were used for the measurement.

The right-side loin of each animal was used to determine colour, shear force and cooking loss. The determination of the colour was performed through a colourimeter (Minolta CR-10, Konica Minolta Sensing Americas, Inc.), using the CIE system L*, a*, b*, which determine the coordinates luminosity (L*: 0 = black; 100 = white), index of red (a*) and index of yellow (b*; Miltenburg et al. 1992). For colour evaluation, six readings were obtained from the Longissimus dorsi muscle (three in the medial portion and three in the lateral portion) of each animal, and an average per animal was then calculated.

Cooking loss was obtained by cutting 25 × 25-mm cubes, measured with a digital caliper, weighed and baked in an electric oven until the temperature of the geometric centre reached 71°C, as monitored by a thermo-couple equipped with a digital reader. Then, the samples were cooled to room temperature and weighed again. Cooking loss was calculated by the weight difference of the samples before and after the heat treatment and was expressed as a percentage, according to the method described by Felicio (1999).

The texture of the meat was measured by shear force, according to the method of Purchas and Aungsupakorn (1993), in the same samples as those used for cooking loss determination. Six 1-cm-diameter cubes were removed from all parts of the Longissimus dorsi with a metallic cylinder. The shear was made perpendicular to the fibres by using a texturometer equipped with a Warner Bratzler blade, operating at 20 cm/min, and the peaks of the shearing force were recorded. Then, the average was calculated for all cubes per animal.

Moisture, ash and crude protein contents were determined in the samples of fresh meat according to the methods described by AOAC (2000). After the extraction of lipids, by the method of Folch et al. (1957), the fatty acids (FA) were methylated and stratified by the method described by Hartman and Lago (1973). The identification and quantification of the esters of FA were obtained by the means of a gas chromatograph 430-GC (Varian, Middelburg, The Netherlands) coupled with a flame ionisation detector. The FA separation happened in a fused silica capillary column CP WAX 52 CB (dimensions of 60 mm × 0.25 mm and 0.25 µm, Agilent, Santa Clara, CA, USA). The samples of methyl esters (1.0 μL) were injected in a split and splitless injector system at 250°C, and the chromatograms were recorded by a software type Galaxie Chromatography Data System (Agilent). The initial and final temperatures of the column were 100°C and 240°C respectively, with a ramp of 2.5°C/min. The temperature of the detector was kept at 250°C.

Peaks of the FA were identified by comparison to their retention time using Supelco-1896 MSDS standards (Merck, Darmstadt, Germany). Once the concentrations were determined, the FA were grouped according to their respective order of nutritional interest.

Data were submitted to polynomial regression through the statistical program SAS (2013), using the following statistical model:

where Y_i = variable response value obtained at the ith level of concentrate (kg/animal.day); β_o = intercept of the regression equation; β₁ = regression coefficient correspondent to linear, quadratic,., kth degree (k = 3); x = ith level of the concentrate intake (kg/animal.day); ϵ = random error.

When the regression fit is linear:

where Y_i = the dependent variable; β0 = intercept; β1 = slope parameter; ϵ = random error.

The Pearson correlation matrix was associated with carcass subcutaneous fat thickness (FT), marbling, shear force, cooking loss, LEA and FT. Once the muscle was exposed, the meat marbling was measured, according to the scale of 1–18 points (Müller 1987). The colour and texture readings of the meat were also taken at the same location, using a scale of 1–5 points (Müller 1987).

The score for subcutaneous fat (SF) in the carcasses was affected quadratically by the concentrate level, with the minimum point (2.35 mm) being at the supplementation level of 1.45 kg/animal.day (Table 3). In the Brazilian system of carcass typification, the degree of carcass finishing, evaluated by the SF score, allows carcasses with a scarce SF to be considered adequate (MAPA 2004). Whereas 3 mm is the minimum FT for a good-quality carcass (Luchiari Filho 2000; Moletta et al. 2014).

Table 3.  Characteristics of the carcass of Nellore steers fed with increasing levels of energy and protein
HCW, hot carcass weight; HCY, hot carcass yield; SF, subcutaneous fat; s.e.m., standard error of the mean

Classifying the postmortem carcasses according to MAPA (2004), they were mostly subconvex (77.5% carcasses), receiving, in accordance with current regulations, a good carcass-grade quality. According to Mendes et al. (2012), greater FT of the carcass means a greater degree of finishing of the animal and a greater protection of the carcass by fat, decreasing the weight loss during the cooling process.

There were no significant differences among the hot carcass weights (P > 0.36; Table 3). According to Silva et al. (2014) and Berg and Butterfield (1979), during the growth and fattening of cattle, the tissue-synthesis rates are influenced mainly by the age, physiological stage, nutrition, genotype and sex of the animal, which alter the physical and chemical composition of the carcass.

As the animal grows, fat is deposited between muscles (intermuscular fat), below the skin (coating or SF), and finally between muscle fibres (marbling or intramuscular fat; Silva et al. (2014). According to Kempster et al. (1988), European breeds differ from zebuine breeds in the distribution of body fat, depositing fat in regions that are not part of the carcass, and, when depositing in the carcass, the deposition is greater intermuscularly than subcutaneously.

Animals with some zebuine lineage are more precocious for deposition of SF (source). All groups presented SFT greater than 3 mm (average 3.12 mm), which is the minimum recommended by the slaughter houses to avoid deductions (Luchiari Filho 2000).

The chemical composition of bovine meat may be influenced by the diet, since it may be associated with other qualitative traits, such as organoleptic traits. According to Prado et al. (2011), the centesimal composition of beef is 74% moisture, 21.4% protein, 1.69% fat, 0.99% ash and 37.8 mg/100 g total cholesterol. These percentages may vary according to the age of the animal, genotype, sex, castration, feeding and pre- and post-slaughter handling.

In the present trial, no effect of protein and energy supplementation was found in the meat pH (P > 0.90). Evaluating the meat quality of Nellore calves, Zorzi et al. (2013) could verify that there was a close relationship between pH and other qualitative traits. After slaughter, the residual metabolic activity of the muscle causes the degradation of glycogen to lactate, which dissociates to lactic acid, causing pH to decrease (Nalbandian and Takeda 2016). Therefore, intracellular concentration of glycogen is responsible for high water-retention capacity.

The pH ranged between 5.64 and 5.71, which is considered suitable for maintaining the meat quality, according to Abularach et al. (1998) and Mach et al. (2008). However, Rossato et al. (2010) reported a range of 5.88–5.95 of final pH for beef from animals finished on pasture. The small range indicated that there was no pre-slaughter stress.

Bressan et al. (2011) observed that finishing beef cattle on pasture or feedlot influences the pH, with pH of feedlot-finished cattle being greater. In contrast, Jaeger et al. (2004) did not find the effect of the diet or genetic group on the pH, with the average pH being 5.79 for Longissimus dorsi of Nellore cattle.

Concentrate intake affected water loss for cooking, which decreased linearly until the supplementation level of concentrate was 2.02 kg/animal.day. Cooking causes structural changes in meat. Cooking temperatures between 54°C and 58°C result in changes in myosin, those between 65°C and 67°C result in changes in collagen, and those in the range of 80–83°C result in actin undergoing changes (Tornberg 2005). The water is expelled by the pressure exerted by this shrinkage in connective tissue, which influences the sensorial perception of juiciness (Silva et al. 2007).

Water retention capacity is another characteristic which is directly associated with juiciness and tenderness of meat (Mendes et al. 2012). It occurs when the pH of the meat remains high, which causes less denaturation and a smaller loss of protein solubility.

Higher water loss for cooking results in a lower meat juiciness, which can reduce its texture, as indicated by shear force (Bressan et al. 2011). In the present study, shear force reduced linearly (P < 0.05, R² = 0.97) with an increase of energy and protein in the diet.

As energy and protein increased in the diet, cooking loss decreased linearly (P = 0.01) and shearing force quadratically (P = 0.02), with a strong correlation between them (r = 0.93). In this way, as cooking loss increases, the shear strength increases, which may affect tenderness and juiciness.

The Pearson’s correlation coefficient between carcass FT and marbling was low, below 0.5, except when the animals received 2.02 kg of concentrate/animal.day (r = 0.74).

Several authors (e.g. Vaz et al. 2007; Menezes et al. 2010) have stated that finishing cattle on pastures results in meat with a greater shear force than does finishing in feedlot, with values ranging from 3.77 to 6.18 kgf for pastures and ~2 kgf for feedlot. In the present study, the values between 2.07 and 2.91 kgf indicated that supplementing steers with energy and protein in the Santa Fe model of integrated crop–livestock system is a feasible way to produce tender meat.

The meat tenderness is also related to carcass finishing degree and intramuscular fat content. The degree of finishing ensures the carcass protection against the cold in cooling chambers, i.e. it ensures that the temperature of the carcass falls gradually, preventing the shortening of tissue sarcomers and reducing the loss by dehydration during cooling (Mendes et al. 2012).

Several factors may influence colour, including diet and final pH. However, the direct effects of diet on meat colour rarely occur and depend on the capability to influence the muscle myoglobin content, as well as the composition of muscle fibre type, which varies according to the age and growth rate. Muscle colour may also reflect intramuscular fat content (Lafaucher 2010).

There were no significant differences in L*, or a* and b* (Table 4), probably because the animals were from the same breed and of a similar age. In addition, concentrate supplementation level and final meat pH did not affect meat colour. The conjunction of these variables located a point in the spherical system of colour, which classified the meat of all treatments as bright red, which is also the preference of the consumers. With concentrate supplementation, LEA (cm) results were adjusted to a cubic equation, without a clear biological response regarding energy and protein levels in the diet.

Table 4.  Physical–chemical traits and centesimal composition of Longissimus dorsi
LEA, loin eye area; FT, subcutaneous fat thickness; *L, luminosity; *a, redness index; *b, yellowness index; s.e.m., standard error of the mean

Studies have shown (Jaeger et al. 2004; Bianchini et al. 2007; Lopes et al. 2012a) that LEA can estimate the proportion of animal’s musculature and yield of high-value cuts, such as fillet and sirloin steaks.

Costa et al. (2005) reported the association of LEA and the thickness of fat coating, evaluated between the 12th and 13th ribs. In the present study, LEA data were better adjusted to a cubic equation (P < 0.05, R² = 0.99), without a clear response to supplementation. However, FT quadratically increased (P < 0.05, R² = 0.94). It is likely that the supplementation levels in the present work were not different enough from one another (0.98, 1.45, 1.86, 2.02 kg/animal.day) to capture the differences observed by Luchiari Filho (2000).

Marbling fat is the last to be deposited in the carcass, and it is influenced by the energy level of the diet and animal weight (Moletta et al. 2014). In the present study, the best marbling (4.42) was observed when concentrate intake was 1.95 kg/animal.day (P < 0.05, R² = 0.75).

According to Luchiari Filho (2000), normal values for chemical composition of the muscle of a young bovine are 74% water, 21% protein, 4% fat and 1% minerals. However, according to this author, several factors influence meat composition, such as the animal age, muscle type, diet and fat, which is the most variable component. In the present study, fat content was not affected by energy and protein supplementation, differently from marbling and fat-thickness trends.

The physical and chemical properties of the lipids directly affect the nutritional, sensorial and conservational meat qualities. The flavour is influenced by the FA profile. Saturated fats solidify after cooking, affecting the residual flavour of the meat. The presence of unsaturated FA increases the oxidation potential, influencing shelf life (Madruga et al. 2006). However, in this trial, no differences in total SFA, monounsaturated fatty acid (MUFA) or PUFA were found (P > 0.05) when energy and protein were increased in the diets.

Due to the association between the production of healthier bovine meat and the use of semi-confinement or other systems, several studies have been conducted to evaluate the effects of animal feeding strategy on the fatty acid profile (Sami et al. 2006; Fernandes et al. 2008; Bressan et al. 2011). These studies have shown different responses in fatty acid (FA) profile because of the diets.

There is evidence that zebu cattle fed with high proportions of concentrate deposit larger amounts of saturated FA (SFA; Bressan et al. 2011), and the FA profile of cereal grains determines the FA found in the meat (Fernandes et al. 2008), which partially disagrees with the results of the present work, because there were no major changes in the concentrations of most SFA, except for C10:0 and C15:0.

However, it should be noted that SFA concentrations of ruminant meats are a result of biohydrogenation in the rumen and de novo synthesis in the adipose tissue (Jenkins et al. 2007). The increase in the SFA concentration is not desirable because it tends to raise both low-density (LDL) and high-density (HDL) lipoproteins. Myristic (C14:0), lauric (C12:0) and palmitic (C16:0) acids are the most worrying due to the hypercholesterolemic action, while stearic acid (C18:0) seems to have neutral effect because they are immediately transformed into oleic acid in the human organism (Hautrive et al. 2012). Consumers are interested in meat with a lower concentration of total lipids, SFA and calories (Clímaco et al. 2011) that makes the meat from cattle fattened in Santa Fe integrated crop–livestock system with concentrate supplementation an attractive option.

The capric acid (C10:0) tended to increase in a linear manner (0.05 < P ≤ 0.1) as the concentrate level was increased. With the concentrate intake of 1.16 kg/animal.day, the maximum concentration of C15:0 was reached (P < 0.05, R² = 0.98), which can be affected by the concentration of propionic acid.

Odd-chain FA in ruminants are formed by de novo synthesis from the propionic acid produced in the ruminal fermentation process (Fernandes et al. 2008). This response may also be related to grain supplementation because it may increase propionate production in the rumen. However, considering that diets had high-lipid grains, it is expected that some influence in ruminal biohydrogenation would occur by inhibiting adhesion of the cellulolytic bacteria to its substrate (Berchielli et al. 2011).

In general, the increase of dietary energy and protein promotes elevation of the concentration of total monounsaturated FA, while the concentration of total PUFA decreases, due to the elevation of meat intramuscular fat (Sami et al. 2006). However, in the present research, marbling and total lipid concentration were not altered by the diets (P > 0.05; Table 5).

Table 5.  Fatty acids (in percentage) in Longissimus dorsi of Nellore steers supplemented with energy and protein in an integrated crop–livestock system
s.e.m., standard error of the mean

The increase of PUFA in the meat has been attributed to genotypes with lower intramuscular fat concentrations (Smith et al. 2009). However, in the present study, an increase in PUFA concentration was found and it has a high degree of association with marbling (R₂ = 0.89).

Linoleic acid (C18:2n6) increased linearly with the energy and protein supplementation (P < 0.05, R² = 0.99). It is the most important FA of the (ω6) series and it is considerably present in vegetable oils such as sunflower oil, safflower, corn, soy, cotton and others. Soybean and cottonseed (high in C18:2n6 lipids) used in the concentrate seems to have undergone ruminal biohydrogenation and then been deposited into the muscles. PUFA had the maximum concentration point (4.66 litholeic acid/area) when the concentrate intake was 1.86 kg/animal.day (Table 5).

The FA from the family ω₃ of nutritional interest are, in addition to α-linolenic acid, its derivatives, namely, eicosapentaenoic acid (C20:5, n3) and docosahexaenoic acid (C22:6, n3; Palmiquist and Griinar 2006). They are found in the oilseeds used in the cattle diet. In this context, the docosahexaenoic acid increased linearly (P < 0.05, R² = 0.82) with increasing energy and protein in the diets (Table 6).

Table 6.  Fatty acids (in percentage) in Longissimus dorsi of Nellore steers supplemented with energy and protein in an integrated crop–livestock system
SFA, saturated fatty acids; MFA, monounsaturated fatty acids; PFA, polyunsaturated fatty acids; UFA, unsaturated fatty acids; DFA, desirable fatty acids; IA, aterogeneity index; CLA, conjugated linoleic acid; ICFA, intermediate chain fatty acids; MCFA, medium-chain fatty acids; LCFA, long-chain fatty acids

Energy and protein levels in the diet affected FA ω₃ concentration (Table 6), which linearly increased (P < 0.05, R² = 0.98) with increasing concentrate supplementation. However, there was no relationship between the concentrate level and the ω₆ : ω₃ ratio, even with a greater percentage of ω₃ in the diet (Darley et al. 2010).

The ω₆ and ω₃ FA have influence on the metabolism of eicosapentaenoic and docosahexaenoic acids, both in gene expression and intercellular communication. The composition of PUFA of cell membranes depends directly on the diet (Harper and Jacobson 2001).

The two classes of PUFA must be well differentiated, as they are metabolically distinct and have opposite physiological functions. Therefore, the nutritional balance is important to achieve homeostasis and normal development of organisms. A correct balance in the ratio of ω₆ : ω₃ in the diet is essential for the metabolism of humans, which may lead to prevention of cardiovascular and chronic degenerative diseases and also a better mental health (Stradiotto et al. 2010). The desired ratio of ω₆ : ω₃ is 1 : 4. The problem in the western diet is basically the imbalance of ω₆ : ω₃, with a high consumption of ω₆ in relation to ω₃ (Ruiz-Núñez et al. 2016). Finishing cattle supplemented with energy and protein in Santa Fe integrated crop–livestock system produced meat with potential increased health benefits, as indicated by the high concentration of ω₃.

Energy and protein supplementation of Nellore steers in Santa Fe integrated crop–livestock system improved meat quality, including attributes such as tenderness and marbling, without excessive deposition of saturated fatty acids. There was positive influence of the concentrate level on the ω₃, making the meat more attractive for human consumption because of its potential health benefits and commercial appeal.

The authors declare no conflicts of interest.