The value of pH is related to muscle glycogen depletion, a factor that can be associated with inappropriate handling of animals (i.e., preslaughter stress), resulting in the appearance of meats known as dark-cutting beef, as described in the literature (Sousa Ribeiro et al., 2022). The average pH values of the carcasses in the present study may be, at least partially, associated with the diet (processing and energy bioavailability) and the appropriate slaughter conditions, irrespective of the C:R ratio. The final pH, a vital parameter to evaluate the levels of lactic acid in the muscle, will be higher when the glycogen reserves are lower, which may compromise the qualitative aspects of the meat (Lawrie and Ledward, 2006). Moreover, pH and temperature measurements are important in monitoring the final quality of the meat, because the hot carcass undergoes acidification and denaturation of proteins, and these factors may interact (Kim et al., 2012).
The diets in this study containing unprocessed silage may have provided the animals with rapid phosphocreatine degradation, which in turn depleted the glycogen and ATP reserves, due to the low energy in the muscles and the reduced bioavailability of energy from the food provided. Consequently, although this did not characterize dark-cutting beef, higher pH values were observed in the carcasses of animals that consumed these diets. Furthermore, light carcasses with low BFT are commonly more subject to fiber shortening by cold, resulting in lower meat tenderness, especially when rapidly cooled (Tait et al., 2005). However, such effects were not observed in the present study.
In addition to HCW, cut yields are positively associated with REA and negatively associated with BFT (Chardulo et al., 2013). Other studies have reported that bovine carcass evaluated as a function of BFT (finishing) and REA (growth or muscularity) can provide parameters indicative of the boning yield of commercial cuts (Delgado-Pando et al., 2021; Maciel et al., 2021). Beef carcasses of the same weight, but with discrepant average BFT and REA, were found to generate variable yields and negatively affect the number of commercial cuts, especially those of higher added value, affecting costs and revenues (Boykin et al., 2017).
Hence, as confirmed in the present study, finishing systems that use feedlot zebu cattle consuming diets containing mechanically processed silage can obtain similar yields of the main meat cuts of higher commercial value, even if trends (P < 0.10) for higher yields of the tenderloin in response to the C:R ratio were verified. Similar results were reported by He et al. (2018) who evaluated two different types of corn silages in beef cattle fed with finishing diets. Yield implies a direct financial return to the producer and the slaughterhouse, as it is directly related to the amount of marketable meat.
The 20:80 C:R ratio tested in the finishing diet yielded meat with an IMF content of 1–3%, which is consistent with the result of another study on beef cattle (Serra et al., 2008). The centesimal composition varied slightly between the LT muscle samples of both treatments, with the maximum variation observed only for the IMF content of meat. In a study by Pereira et al. (2010) on F1 Angus–Nellore cattle, similar centesimal composition values as those in the present study were observed, with the average values being 75.57%, 1.08%, and 22.20% for moisture, ash, and protein contents, respectively. Moreover, Costa et al. (2007) analyzed meat from beef cattle and found similar average values for protein (23.1%), IMF (2.4%), and ash (1.5%) contents as those observed in the present study.
The nature and amount of lipids stored in the muscle are dependent on feeding conditions, digestion, intestinal absorption, liver metabolism, and the transport system of these lipids. The results of IMF content in the present study were similar to those found by Neumann et al. (2008) who evaluated the meat characteristics of Charolais cattle as a function of the effect of corn silage particle size. The characteristics related to IMF deposition can positively influence the sensory attributes of meat, including taste, flavor, juiciness, and tenderness, as reported (Hocquette et al., 2010).
Regarding the color variables, the values found in this study were similar to those described by Muchenje et al. (2009), who reported a lightness (L*) average range of 33–41, a red parameter (a*) value of 11–23.5, and a yellow parameter (b*) value of 6–11. The results of the present study corroborate those reported by other researchers in the literature (Pflanzer and de Felício, 2011; Lopes et al., 2020) for the aspect of meat color. The color observed on the meat surface is a consequence of light absorption by myoglobin and other components, such as muscle fibers and their proteins, and is also affected by the amount of water in the extracellular space. In general, the lower the sarcoplasmic protein content on the surface of myofibrils, the less light scattering occurs, resulting in darker colored meats (Suman et al., 2014).
In the present study, the treatments possibly did not affect the sarcoplasmic proteins, which generated similar coloration results for both meat and fat. We evaluated the meat color because such characteristics comprise a primary aspect to be considered when purchasing meat at retail, in addition to food safety (origin and the brand of the product), type and size of cut, fat cover, and meat tenderness. For classifying meat that is most likely to have tenderness and juiciness, consumers generally look at meat coloration and cut size and particularly the amount of marbling or IMF and subcutaneous fat (Chardulo et al., 2013).
Although meat tenderness was not affected by the treatments, it was noticed that the mean WBSF observed (7.37 ± 0.23 kg) characterized the meat of Nellore cattle as tough in the present study, considering the WBSF reported in the literature for meat classification as tender (Rodas-González et al., 2009), i.e., < 4.9 kg. This condition can be explained by the fact that the meats in the present study were not submitted to aging for a period of more than 7 days. However, the toughness of the meat verified in both treatments can be associated with the losses that occurred during the cooking process. The CL was in the range of 23.21–28.66%, a value that can be considered to be higher than that reported in the literature (Rivaroli et al., 2016). In a previous study on LT muscle samples obtained from 1652 feedlot-finished Nellore bulls, a biological model similar to that used in the present study (Baldassini et al., 2017), only 11.2% of samples were considered to be tender (WBSF ≤ 4.9 kg) and had lower CL.
Mechanical processing of corn silage and its inclusion in feedlot diets, irrespective of 20% or 40% of dietary DM, can provide better carcass pH of Nellore cattle, without negatively influencing other growth characteristics (muscularity and yield of cuts), fatness (BFT), and meat quality traits (color, WBSF and CL).
In the biological production model adopted in the present study (uncastrated male zebu cattle), better results on IMF content were obtained when a higher proportion of concentrate was used in the finishing diet, irrespective of corn silage processing.
Based on the cost evaluation of the experimental diets, mechanical processing of corn silage could be recommended for diets with a higher proportion of concentrated feed (i.e., 20:80 C:R ratio), enabling better economical diets for finishing feedlot Nellore cattle. The cost differences ($/@ produced, $/animal/day, total feedlot, and $/ton DM) among the 60:40 C:R ratio diets were less discrepant, with a small economic advantage observed for diets containing unprocessed silage.