The current study evaluated growth performance and digestion responses of finishing bulls fed diets containing 825 g/kg flint maize [dry matter (DM) basis] ground to medium (1.66 mm; MG) or coarse particle sizes (2.12 mm; CG), with added monensin (26 mg/kg; DM basis; MON) or a blend of essential oils (BEO) + exogenous α-amylase (AM; 90 mg/kg + 560 mg/kg commercial product, respectively, DM basis). In Expt 1, 256 Nellore bulls were blocked by initial body weight (BW) (360 ± 11.7 kg) and assigned to 48 pens in a 2 × 2 factorial arrangement of treatments. Effect of a maize particle size × feed additive interaction was not detected for final BW, DM intake (DMI), average daily gain (ADG) and feed efficiency. The DMI was greater for bulls fed BEO + AM v. MON. Final BW and ADG tended to be greater for bulls fed CG than MG maize. An interaction was detected for hot carcass weight which was 11 kg heavier for bulls fed BEO + AM v. MON in diets containing CG, but not MG particle size. In Expt 2, four ruminally cannulated Nellore steers were offered the same treatments as Expt 1, in a 4 × 4 Latin Square design. Intake of most nutrients was greater for steers fed CG than steers fed MG maize. In summary, feeding bulls CG maize increased growth performance and carcass characteristics compared with MG. The combination of BEO + AM resulted in heavier carcass weights compared with MON supplementation when included in diets containing CG maize.

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The determination of kinetic data is central to reaction mechanism; science courses usually include experiments on chemical kinetics. Thanks to PC-controlled data acquisition and availability of software, the students calculate rate constants, whether the experiment has been done properly or not. This contrasts with their experience in, e.g., organic synthesis, where a broad melting point indicates an impure product. In order to teach quality kinetics and link theory to experiment, we used a multistep project, based on the (convenient) pH-independent hydrolysis of 4-nitrophenyl chloroformate in aqueous organic solvents. The steps of the project included statement of the experiment's objective; a quiz on reaction mechanism and experimental techniques in chemical kinetics; students' decision on the organic solvent to be employed; extraclass activity to assess their choice of the solvent; carrying out the experiment; and discussion of the results obtained. We have applied the constructivist approach to illustrate that controlling the experimental conditions (solution temperature and homogeneity) is a prerequisite for obtaining quality kinetic data. The students' evaluation was highly positive because they participated in the different steps of the project.

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