Effects of different doses of sodium monensin on rumen papillae and tissue histology of feedlot Nellore cattle

The experiment was designed to determine the effects of different doses of sodium monensin (MON) on rumen papillae and tissue histology of feedlot Nellore cattle. The experiment was designed as a completely randomised block, replicated 12 times, in which 60 20-month-old yearling Nellore bulls (402.52 ± 33.0 kg) were fed in individual pens for 84 days according to the following doses of MON expressed in ppm (on a dry-matter basis): 0, 9, 18, 27 and 36. The adaptation program consisted of ad libitum feeding of two adaptation diets over a period of 14 days, with concentrate level increasing from 68% to 84% of diet dry matter. Orthogonal contrasts were used to assess linear, quadratic, cubic and quartic relationships between doses of MON and the dependent variable. No significant (P > 0.10) MON effect was observed for number of papillae, mean papillae area, papillae area as a percentage of absorptive surface and rumenitis incidence. However, as the dose of MON increased, the absorptive surface area, papillae surface area and mitotic index were affected (P < 0.05) cubically, in which animals fed 9 and 36 ppm presented larger absorptive surface area and greater number of cells in mitosis. Thus, based on the results, feeding of MON affected rumen papillae and tissue histology of feedlot Nellore cattle. The doses of 9 or 36 ppm of MON should be considered as the most feasible options, because they promote better development of rumen epithelium.