Carcass traits and meat quality of steers fed palm kernel cake as a replacement for grain sorghum

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2021), but does not seem to interfere with the physicochemical traits of goat meat (Ribeiro et al., 2018).In feedlot cattle, preliminary studies (Santana Filho et al., 2016;Cruz et al., 2018) have showed a linear decrease in performance and carcass weight and no changes in the physicochemical traits of meat in response to the dietary inclusion of PKC.In this respect, there is little evidence in the literature about the use of PKC for feedlot cattle, especially in high-grain diets, and its effects on the carcass and meat of these animals.
The hypothesis of this study was that the concentrations of inclusion of palm kernel cake up to 240 g/kg in the diet of confined, crossbred cattle could improve the carcass traits and meat quality of these animals.This study thus proposed to investigate the effects of replacing grain sorghum with palm kernel cake on the carcass traits and meat quality of feedlot steers fed high-grain diets.
The present study was approved by the Ethics Committee on Animal Use at the State University of Southwest Bahia (approval no.45/2013).Forty uncastrated, half-blood, Holstein × Zebu crossbred cattle at an average age of 24 ± 2 months, with an initial average weight of 331.1 ± 36.2 kg, were housed in group stalls (10 animals/stall) with a usable area of 100 m 2 (10 × 10 m), with 50 m² of cement floor and 50 m² partially covered.The stalls were equipped with covered concrete feeders (10 linear meters) and drinkers of 250-L capacity.The animals were weighed, identified with plastic eartags, and dewormed (Abamectin-1% -Abmic® Microsules).After weighing, they were randomly distributed into four treatments in a completely randomized design with ten replicates.The treatments consisted of diets containing 0 (control), 80, 160, or 240 g/kg of PKC on a dietary dry matter (DM) basis (Table 1).Composition: calcium 140 g, phosphorus 65 g, sodium 148 g, magnesium 5 g, sulphur 12 g, cobalt 107 mg, copper 1,550 mg, iodine 150 mg, manganese 1,400 mg, nickel 30 mg, selenium 18 mg, zinc 4,500 mg, 1,120 mg, fluorine (maximum) 650 mg 2 g/kg fresh matter 3 neutral detergent fibre corrections for protein and ash 4 acid detergent fibre 5 metabolizable energy For information on feed composition, animal management during the feedlot period and estimates of nutrient intake and digestibility and animal performance, see Lisboa et al. (2021).
After 126 days, the animals were weighed without previous fasting.Subsequently, they were deprived of solid and liquid feed for 12 h to determine the final body weight (FBW) and the empty body weight (EBW).After fasting, the animals were slaughtered, skinned, and eviscerated in a commercial slaughterhouse in Itapetinga -BA, Brazil, following current law (Brasil, 2000).The carcass of each animal was sawn lengthwise along the sternum and spine, producing two similar halves, which were weighed to determine the hot carcass weight (HCW).Hot carcass yield (HCY) was calculated as HCW/EBW (Gomes et al., 2021).Gain yield (GY) was calculated using the following equation: Carcass gain (GC), in turn, was calculated using the following equation: GC (kg) = (Gain yield × Average daily gain)/100 (2) The right half-carcasses were identified and stored in a cold chamber, where they were kept at 4 °C for 24 h.After this period, the carcasses were measured to determine carcass and leg lengths and beef round thickness.Carcass conformation was evaluated according to the scale suggested by Gomes et al. (2021).
Ribeye area was measured on the right side of the carcass by making a cross-section between the 12th and 13th ribs and exposing the longissimus lumborum muscle.Then, its outline was traced on parchment paper and the area was later measured with a planimeter.Subcutaneous fat thickness was determined as the average of three measurements at equidistant points, using a precision calliper, in the region of the section between the 12th and 13th ribs.'Ratio', a measurement that characterizes the ratio between the height and width of the longissimus lumborum muscle (obtained using a graduated ruler), was also determined.
A sample of the Longissimus dorsi muscle was dissected between the 10th and 13th ribs in each right half-carcass, wrapped in film, placed in high-density plastic bags, and covered with aluminium foil.Muscle samples were stored in a freezer at -10 ºC for 60 d until laboratory analysis.To determine the physicochemical parameters in the logical order of analysis, the colour was first determined, followed by cooking loss and shear force.In parallel, water-holding capacity and the ionic potential of hydrogen were measured, following the methodologies described by Ramos & Gomide (2017).
The pH was determined in triplicate, using a Quimis 0400MT benchtop pH meter.For chemical analysis, the samples were thawed at room temperature, the subcutaneous fat was removed, and the muscle was lyophilized to determine the moisture, ash, and crude protein contents, following the methodology proposed in AOAC (2000).Total lipids were determined using a method adapted from Bligh & Dyer (1959).Total cholesterol was extracted according to the method described by Al-Hasani et al. (1993).
The data were evaluated according to the following statistical model: where Yij = experimental response measured in treatment i and replicate j; µ = overall constant; Ti = effect of treatment i, where i = 0, 80, 160, and 240; B(Xij -X) = effect of covariate (initial weight); and eij = random error associated with each observation.The data were subjected to analyses of variance and regression using the GLM and REG procedures of Statistical Analyses System software.
The replacement of GS with PKC caused the metabolizable energy intake of the animals to decrease linearly (P <0.05) but did not influence (P >0.05) digestible protein intake or final body weight (Table 2).
Whereas the meat pH increased linearly (P <0.05), there were no changes in cooking loss (32.42 ± 42.35%), water-holding capacity (69.21 ±1.73%), shear force (3.35 ± 0.32 kgF), or the objective colour parameters of the meat (Table 3).The replacement of GS with PKC did not influence (P >0.05) the moisture (72.68 ± 1.03%), fat (3.42 ± 0.27%), or cholesterol (40.03 ± 2.98 mg/100 g) contents of the meat (Longissimus).The decrease in metabolizable energy intake did not influence empty body weight.This was possibly because the replacement of the starch from GS with PKC reduced the heat increment of feeding and provided more net energy for gain in the steers that consumed PKC.Additionally, digestible protein intake was similar between the treatment groups.In contrast, Cruz et al. (2018) and Santos et al. (2019) reported decreases in the crude protein intake and final weight of steers and cull cows, respectively, following the inclusion of PKC in the diet.
Hot carcass weight and carcass gain were not influenced by the inclusion of PKC in the diet, possibly because of the observed similarity in empty body weight between the treatment groups.Hot carcass weight has a strong positive correlation with slaughter weight in cattle (Façanha et al., 2014).In addition, the produced carcasses met the standard weight required by the Brazilian domestic market (minimum of 225 kg) for Zebu animals.Gordo et al. (2018) recently reported a carcass weight of 272 ± 24.70 kg in animals slaughtered in Brazil.
The average carcass gain observed in this study was compatible with high-grain diets, indicating that even with the inclusion of a byproduct and the removal of part of the starch from the diet, the efficiency of nutrient conversion into carcass was high for Zebu animals (Paulino et al., 2013).Benediti et al. (2016) also did not observe an effect of replacing corn with crude glycerine on the carcass gain of cattle.
The reduced subcutaneous fat thickness may be attributed to a decreased synthesis of short-chain fatty acids (SCFA) in the cattle rumen induced by the reduced presence of GS in the diet (Gómez et al., 2016).Lower levels of SCFA-acetate and butyrate, mainly-in the peripheral circulation result in fewer acetyl units for fatty acid synthesis in subcutaneous adipocytes in cattle (Park et al., 2018).Although low by international standards, the average subcutaneous fat thickness found in the present study (3.21-3.50mm) was considered adequate for Zebu carcasses.Bonin et al. (2021), for instance, reported an average fat thickness of 3.59 mm in the carcasses of animals slaughtered in Brazil.
It is possible that the lower presence of GS in the diet (resulting from its replacement with PKC) impaired the synthesis of rumen propionate (Lage et al., 2017).This SCFA is involved in the processes of hepatic gluconeogenesis and hepatic and muscle glycogenesis (Gardner et al., 2014).Therefore, the animals fed PKC might have produced less rumen propionate, which led to lower muscle glycogen stores and, consequently, a higher final pH of their meat.
Despite the observed decrease in the final pH of the meat, the physicochemical parameters of cooking loss and water-holding capacity were not influenced.We suggest that the increase in the final pH of the meat (0.056 at each 80 g/kg PKC) of the animals fed PKC was not sufficient to elicit consistent changes in water retention within the myofibrillar proteins (Peace et al., 2011).
Water retention, in turn, influences lightness (Rosa et al., 2016) and, together with other objective colour measurements (a* and b*), these two variables were similar between the treatment groups.Besides the pH, the similar age and physiological stage of the animals likely contributed to the observed proximity of objective colour parameters (Hughes et al., 2014).Oliveira et al. (2020) evaluated the meat of feedlot-finished Nellore cattle and found L*, a*, and b* values of 34.38, 17.92, and 9.9, respectively.In addition to the colour, the tenderness of meat is also markedly influenced by age, particularly in terms of collagen solubility (Pacheco et al., 2020).Thus, the lack of effects of PKC inclusion on tenderness (shear force) is due to the similar age of the animals at slaughter.Santana Filho et al. (2016) also did not observe an effect of including 210 g/kg PKC on the cooking loss, water-holding capacity, shear force, or colour parameters of beef.
Even with the increase in the EE content of the diet provided by the inclusion of PKC, the steers produced meat with a low fat content (3.42% EE) (Casperson et al., 2020).This low intramuscular fat content is possibly due to the fact that the experimental animals -uncastrated Nellore slaughtered at 485 kg-had not yet reached mature weight for intact Nellore males (Silva et al., 2013).Despite the increase in the EE content of the experimental diets, the cholesterol content of the steers' meat was not altered by the dietary inclusion of PKC, possibly because the endogenous synthesis of cholesterol depends more on acetyl units.Silva et al. (2021) also reported no influence of the inclusion of licuri cake (Syagrus coronate) in the diet on the proximate composition of the meat of steers.
The partial replacement (41,57%) of grain sorghum with palm kernel cake in high-grain diets for feedlot steers reduces the thickness of subcutaneous fat in their carcass but does not interfere with carcass weight or meat tenderness, colour, and composition.The inclusion of 240 g/kg palm kernel cake in high-grain diets for feedlot steers is recommended.

Table 1 .
Feed ingredients and chemical composition of the experimental diets (g/kg DM)

Table 2 .
Performance and carcass traits of steers fed palm kernel cake as a replacement for grain sorghum

Table 3 .
Chemical composition and cholesterol content of the Longissimus dorsi muscle of steers fed palm kernel cake as a replacement for grain sorghum