Abstract
Simple SummaryRanchers in tropical savannas must alter management to deal with forage shortages during seasonal droughts while adding value to their calf crop. Castration, pasture supplementation, and growth-promoting implant protocol (GPIP) can improve growth performance, carcass yield, and perhaps meat quality, potentially increasing profitability. The researchers measured the effects of pasture supplementation and GPIP use in bulls (Experiment I) and/or steers (Experiment II). Bulls offered a strategic protein-energy supplementation (SS) outperformed those offered a traditional mineral mix (MS) in live weight gains, carcass yield, and yield of expensive meat cuts. A combination of a high-potency implant (HPI) followed by a low-potency implant (LPI) resulted in more tender steaks from SS bulls. Tenderness was improved by HPI-LPI in SS bulls or by LPI in SS steers. It is concluded that (a) SS improved growth performance and carcass yield of bulls, while castration improved carcass quality (grading); and (b) the response to GPIP in cutability and tenderness was dependent on castration status. These results are useful for ranchers finishing calves in tropical savannas worldwide.The effects of castration, supplementation, and implant protocol (IP) on growth, carcass characteristics, and meat quality of grass-fed cattle were evaluated. Two experiments followed a two-way ANOVA and a 2 × 2 factorial arrangement. Experiment-I, 99 bulls were evaluated for: (a) supplementation (mineral (MS) or strategic protein-energy supplementation (SS), and (b) IP (repeated (day-0 and day-90) Zeranol-72 mg implantation (Zeranol–Zeranol) or Trenbolone Acetate-140 mg/Estradiol-20 mg (day-0) followed by Zeranol-72 mg (day-90) (TBA/E2–Zeranol). Experiment II, 50 animals were evaluated for: (a) IP (like Experiment-I), and (b) male class (steers vs. bulls). In Experiment-I, SS bulls had greater growth rate, carcass yield, and yield of high-valued boneless lean cuts than MS bulls, while decreasing (p < 0.05) time to harvest. Steaks from SS-bulls on TBA/E2–Zeranol IP were more (p = 0.05) tender than SS/Zeranol–Zeranol counterparts. Experiment-II bulls had greater growth than steers, but decreased (p < 0.05) carcass quality aspects. Zeranol–Zeranol increased (p < 0.01) meat tenderness of steers. Interactions (p < 0.05) affected cutability (Experiment-II) and meat sensory traits (Experiment-I/II). The SS improved growth, carcass yield, and shortened days until harvest of bulls, while TBA/E2–Zeranol IP positively affected tenderness in bull meat only. Castration improved carcass quality while the implant effects on cutability and tenderness were male-class dependent.
Highlights
Non-castrated zebu-influenced calves are the main crop of cow–calf ranches operating in the savanna ecosystem of Venezuela [1]
Most bulls subjected to strategic supplementation (SS) reached the desired endpoint earlier than those subjected to mineral supplementation (MS) (Table 2)
The sensory ratings for the TBA/E2-ZER bull steaks in both experiments and for ZER-ZER steer steaks in Experiment II were below 5, and the mean Warner–Bratzler shear force (WBSF) value was greater than the tenderness threshold (WBSF = 4.09 kg) of Rodas-Gonzalez et al [46]. These results indicate that the degrees of improvement in palatability traits with any of the tested implant protocols were not good enough from the consumer acceptability standpoint
Summary
Non-castrated zebu-influenced calves are the main crop of cow–calf ranches operating in the savanna ecosystem of Venezuela [1]. Experiences on the combined effects of re-implant protocols and strategic supplementation on cutability (fabrication yield) and meat quality of grass-fed, tropical cattle are very rare. It was hypothesized that the combined use of implant protocols and strategic supplementation with or without castration makes feasible quality-pasture-finish of young cattle in grass-fed systems under tropical savannas conditions by positively affecting days until harvest, carcass yield, quality grade, fabrication yield of commercial cuts, and meat quality of Brahman-influenced cattle. A previous assessment was conducted in the Apure’s savannas [35] to evaluate the responses in fattening performance, carcass traits, and carcass classification/grading of grazing bulls exposed to implant protocols (ZER-ZER vs TBA/E2-ZER), while supplementation of cultivated pastures was conducted during the dry season. A follow-up to the study by Huerta-Leidenz et al [35] is presented to further explore the effects of implant protocol and pasture supplementation on fattening performance traits and cold carcass yield of bulls and examine the responses to treatments in fabrication yield and meat
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