The energy content of finishing diets offered to feedlot cattle may vary across countries. We assumed that the lower is the energy content of the finishing diet, the shorter can be the adaptation period to high-concentrate diets without negatively impacting rumen health while still improving feedlot performance. This study was designed to determine the effects of adaptation periods of 6, 9, 14 and 21 days on feedlot performance, feeding behaviour, blood gas profile, carcass characteristics and rumen morphometrics of Nellore cattle. The experiment was designed as a completely randomised block, replicated 6 times, in which 96 20-month-old yearling Nellore bulls (391.1 ± 30.9 kg) were fed in 24 pens (4 animals/pen) according to the adaptation period adopted: 6, 9, 14 or 21 days. The adaptation diets contained 70%, 75% and 80.5% concentrate, and the finishing diet contained 86% concentrate. After adaptation, one animal per pen was slaughtered (n = 24) for rumen morphometric evaluations and the remaining 72 animals were harvested after 88 days on feed. Orthogonal contrasts were used to assess linear, quadratic and cubic relationships between days of adaptation and the dependent variable. Overall, as days of adaptation increased, final BW (P = 0.06), average daily gain (ADG) (P = 0.07), hot carcass weight (P = 0.04) and gain to feed ratio (G : F) (P = 0.07) were affected quadratically, in which yearling bulls adapted by 14 days presented greater final BW, ADG, hot carcass weight and improved G : F. No significant (P > 0.10) days of adaptation effect was observed for any of feeding behaviour variables. As days of adaptation increased, the absorptive surface area of the rumen was affected cubically, where yearling bulls adapted by 14 days presented greater absorptive surface area (P = 0.03). Thus, Nellore yearling bulls should be adapted by 14 days because it led to improved feedlot performance and greater development of rumen epithelium without increasing rumenitis scores.

This experiment was designed to evaluate the effects of lipid source and fatty acid (FA) profile on intake, performance, carcass characteristics, expression of enzymes, and sensorial analysis of B. indicus animals offered a high-concentrate diet. On day 0, 96 non-castrated animals were blocked by initial body weight (400 ± 19.3 kg), randomly allocated to 1 of 24 pens (4 animals/pen), and pens were randomly assigned to receive: 1) Control: basal diet composed of whole cottonseed and corn germ as lipid substrates (CONT; n = 6), 2) Calcium salts of fatty acids (CSFA) of soybean: CSFA of soybean oil as replacement for whole cottonseed and corn germ (CSSO; n = 6), 3) CSFA-Blend: CSFA of palm, cottonseed, and soybean oil as replacement for whole cottonseed and corn germ (CSVO; n = 6), and 4) Mix: basal diet containing whole cottonseed, corn germ, and CSVO (MIXT; n = 6). Experiment lasted 108 d and performance, ultrasound measurements, as well as carcass characteristics were evaluated. Additionally, meat FA profile, expression of enzymes involved in lipid metabolism, and sensorial analysis were evaluated. No treatment effects were observed on performance variables, ultrasound, and carcass traits (P ≥ 0.22), whereas animals receiving CONT had a greater intake of C10:0, C16:0, C16:1 trans-9, C18:1 cis-9, C18:2, C18:3, total FA, monounsatured FA (MUFA), and polyunsaturated FA (PUFA) vs. CSSO and MIXT (P < 0.05). Conversely, intake ratios of saturated FA (SFA):MUFA and SFA:PUFA were all reduced for CONT vs. other treatments. Meat obtained from CONT animals had greater colorimetric (L*, a*, and b*) values vs. MIXT (P < 0.01). On meat FA profile, CONT increased C18:0 vs. supplementation with calcium salts (P < 0.02) and supplementation with CSSO yielded greater meat concentrations of C18:1 trans-10 and C18:2 CLA intermediates (P < 0.01). Expression of SREBP-1, SCD, and LPL was downregulated for CSSO (P < 0.05). For sensorial analysis, regular flavor was greater (P = 0.01) for CSSO vs. other treatments, but also greater aroma (P = 0.05) vs. CONT and CSVO. In summary, addition of different lipid sources with varying FA profile into high-concentrate diets did not affect performance and carcass characteristics of B. indicus animals, but supplementation with calcium salts of soybean oil inhibited the mRNA expression of enzymes involved in lipid metabolism, whereas flavour and aroma were positively impacted by this lipid source.

The objective was to evaluate the effects of 25-hydroxycholecalciferol (HyD®, DSM Produtos Nutricionais Brasil S.A.) supplementation in expression of genes related to anabolism and catabolism of feedlot cattle. A total of 120 Nellore bulls (IBW = 370±20 kg) were distributed in 24 fully roofed-pens with concrete floor (5 animals/pen) in a randomized complete block design (8 pens/treatment). The treatments were T1 (control): no supplementation of HyD®; T2: HyD® supplementation at 1 mg/animal/day; T3: HyD® supplementation at 3 mg/animal/day. Basal diet was formulated to meet requirements of finishing bulls, considering an ADG of 1.6 kg/day (Level 2 Nutrition System, Fox et al., 2004). Adaptation to diets followed a step-up scheme for 14 days, with concentrate inclusion being gradually increased from 76 to 91% DM. Finishing diets were offered from 15th to 100th day of feedlot period and animals fed twice a day (0800 and 1500), with bunks managed for a maximum of 5% orts. After slaughter, muscle samples were collected for quantitative evaluation of gene expression using RT-qPCR method, considering the following genes: SOD1 (antioxidant marker), IGF1, IGF2 and MTOR (anabolism), FOXO1, MURF1, Atrogin-1 and MSTN (catabolism). Statistical analysis was performed using PROC MIXED of SAS® and means compared by Tukey test at 5% probability. No significant differences among treatments were observed for SOD1, FOXO1, MURF1 and Atrogin-1 expression (P >0.05). However, tendencies (0.05 > P ≤0.10) could be observed for IGF1, IGF2, MTOR and MSTN expression in animals receiving HyD®, regardless of dosage. These results indicate a positive effect of HyD® on muscular anabolism and protein synthesis on feedlot finishing cattle. Moreover, the greater expression on MSTN suggest a higher protein turnover and muscular growth regulation. In conclusion, HyD® supplementation increased expression of genes correlated to muscular growth and protein synthesis, being a viable technology for beef cattle finished in feedlot systems.

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