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

Abstract Text:  This study, conducted at the São Paulo State University feedlot, Dracena Campus, Brazil, was designed to determine the effects of different doses of sodium monensin on rumen tissue histological variables of feedlot cattle. The experiment was designed as a completely randomized block, with 12 replications per treatment, in which 60 20-mo-old yearling Nellore bulls (402.52 ± 33.0 kg) were fed in individual pens for 84 days according to the different doses of monensin (DM basis): 1) 0 ppm (D0); 2) 9 ppm (D9); 3) 18 ppm (D18); 4) 27 ppm (D27), and 5) 36 ppm (D36). The adaptation program consisted of ad libitum feeding of two adaptation diets over period of 14-d with concentrate level increasing from 68% to 84% of diet DM. The finishing diet contained: 71.5% cracked corn grain, 16.0% sugarcane bagasse, 7.7% soybean meal, 3.0% supplement, 1.2% urea, and 0.6% limestone (DM basis). At harvest, a 1-cm² fragment of each rumen (n = 60) was collected from ventral sac for histological assessment. Histological sections were stained with hematoxylin and eosin, embedded in paraffin wax, and sectioned. Morphometric measurements, such as papillae surface area, papillae height, papillae width, keratinized layer thickness, and mitotic index, were determined in four papillae per animal using computer-aided light microscope image analysis. Orthogonal contrasts were used to evaluate linear, quadratic, cubic and quartic relationship between doses of monensin and the dependent variable. The use of different doses of sodium monensin did not affect (P > 0.10) keratinized layer thickness. However, as doses of sodium monensin increased, papillae width in mm (D0 = 0.46; D9 = 0.42; D18 = 0.44; D27 = 0.45; D36 = 0.38), papillae surface area in cm² (D0 = 2.43; D9 = 2.12; D18 = 2,25; D27 = 2.68; D36 = 1.72) and mitotic index, as % of basal cells  (D0 = 2.57; D9 = 3.15; D18 = 2.92; D27 = 2.71; D36 = 3.11) were affected (P < 0.05) cubically. The papillae height in mm (D0 = 4.98; D9 = 5.42; D18 = 5.04; D27 = 6.21; D36 = 4.71) was affected (P = 0.05) quadratically as dose of sodium monensin increased. Thus, increasing doses of sodium monensin affected histological variables of rumen tissue. The feeding of either 9 ppm or 27 ppm of sodium monensin seemed to be the best options in this study.

Keywords: Nellore, mitosis, papillae