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Feedlot cattle are usually adapted to high-concentrate diets containing sodium monensin (MON) in more than 14 days. However, for finishing diets with lower energy content, the use of MON during adaptation may hold dry matter intake (DMI), and virginiamycin (VM) may be an alternative. This study was designed to determine the potential of shortening the adaptation of Nellore cattle to high-concentrate diets using only VM as a sole feed additive relative to feedlot performance, feeding behavior, and ruminal and cecum morphometrics. The experiment was designed as a completely randomized block replicated six times (four animals/pen) in which 120 Nellore bulls (390.4 ± 19.0 kg) were fed in 30 pens for 111 days according to the following treatments: (1) MON and adaptation for 14 days (MON14), (2) MON + VM and adaptation for 14 days (MONVM14), (3) VM and adaptation for 14 days (VM14), (4) VM and adaptation for 9 days (VM9), and (5) VM and adaptation for 6 days (VM6). At the end of the adaptation, 30 animals (n = 1 per pen) were randomly slaughtered for rumen and cecum evaluations. The remaining 90 bulls were harvested at the end of the study. No effects of treatments were observed (P < 0.10) for final body weight, average daily gain (ADG), and hot carcass weight (HCW). Cattle fed VM14 presented a greater (P ≤ 0.03) DMI, expressed as percent of body weight (BW), than animals fed either MON14 or MONVM14; however, cattle fed either MON14 or MONVM14 improved (P ≤ 0.02) the gain-to-feed ratio (G/F) by 10.4 or 8.1%, respectively, when compared to bulls fed VM14. Bulls fed VM14 had smaller (P < 0.05) papillae area (0.34 vs. 0.42 cm2) and rumen absorptive surface area (28.9 vs. 33.8 cm2) than those fed MON14. The shortening of the adaptation period linearly decreased the 12th rib fat (P = 0.02) and biceps femoris fat daily gain (P = 0.02) of Nellore bulls fed only VM, which linearly decreased the final biceps femoris fat thickness (P < 0.01). Feedlot cattle fed VM as a sole feed additive should not be adapted to high-concentrate diets in less than 14 days. Regardless of either adaptation length or feed additive, feedlot cattle need at least 14 days to adapt to finishing diets.

The objective of this study was to analyze the effects of anthelmintic treatment and supplementation of post-weaning Nellore calves. The parasitism degree, hematological changes and animal performance were analyzed, as well as the financial viability. One hundred contemporary Nellore calves were used. Animals were divided into four groups: CS+AT: supplementation with concentrate and anthelmintic treatment; CS: supplementation with concentrate; PS+AT: protein mineral supplementation and anthelmintic treatment; PS: protein mineral supplementation. Coproparasitological, hematological, and cost examinations were performed, and productive performance was also evaluated. A completely randomized design was used. Animals that received CS+AT showed greater weight gain. In females, there was significant difference in egg counts per gram of feces only between the CS and PS+AT. In males, animals receiving CS+AT, CS, and PS+AT differ from those receiving PS. No significant effects were observed for total plasma protein, packed cell volume, and eosinophils count. Females which received PS+AT and males who received CS+AT showed higher profitability. This study concludes that effective anthelmintic use is still viable, with higher profitability associated with concentrated supplementation in males, and mineral protein supplementation in females. Male calves show better return over investment when compared to females, due to the higher market value and higher potential performance.

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