Growth, physiological responses, and meat quality of feedlot-finished Bonsmara steers offered unprocessed Mucuna pruriens utilis seed meal with or without conventional and green zinc oxide nanoparticles

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Feedlot finishing of beef cattle on commercial nutrient-dense diets based on expensive corn (maize), soybean meal (SBM) and other commonly used protein-rich ingredients is economically unsustainable, especially for smallholder farmers. Rich in energy and proteins, Mucuna pruriens utilis seed meal (MSM) could replace corn and protein-rich ingredients in beef cattle diets provided its problems of antinutritional factors (ANFs) and high fiber content that compromise animal growth performance are resolved. The objective of this study was, therefore, to investigate the effects of incorporation of conventional (C-Nano-ZnO) versus green (G-Nano-ZnO) zinc oxide (ZnO) nanoparticles in the diets of feedlot-finished Bonsmara steers supplemented with 20% MSM (dry matter basis). In a completely randomized design, 28 Bonsmara steers were randomly allocated to 4 experimental diets [i.e., Control diet without MSM (C); C with 20% MSM replacing corn (partially) and the common protein-rich ingredients (CM); CM with 25 mg/kg C-Nano-ZnO (CM-C); and CM with 25 mg/kg G-Nano-ZnO (CM-G)] each with seven replicates for 98 days. Performance variables, carcass traits, hemato-biochemistry, and meat quality were then measured. All data were analyzed with SAS using one-way ANOVA applying the GLM procedure, with diet as the independent variable, except for growth performance data that were analyzed as repeated measures. Results showed that while dietary MSM did not affect (P > 0.05) meat quality and serum biochemistry, it decreased body weight gain (BWG; P < 0.01), feed intake (FI; P = 0.001), feed conversion efficiency (FCE; P < 0.01), carcass fatness (P = 0.05), hot carcass weight (HCW; P < 0.05), cold carcass weight (CCW; P = 0.05), blood MCV (P < 0.05), MCH (P < 0.01), and neutrophils (P < 0.01) as it increased blood lymphocytes (P < 0.001). Interestingly, the harmful effects of MSM were attenuated by C-Nano-ZnO and worsened by G-Nano-ZnO. In conclusion, feeding of high dietary unprocessed MSM did not affect Bonsmara beef meat quality and serum biochemistry but compromised their growth performance, carcass traits, and some hematology responses, and these were alleviated by C-Nano-ZnO and deteriorated by G-Nano-ZnO incorporation. We recommend feeding commercial diets supplemented with 20% MSM, replacing corn and commonly used protein-rich ingredients, plus 25 mg/kg of C-Nano-ZnO to feedlot-finishing beef cattle.