Effects of different doses of sodium monensin on DMI variation and selective consumption by feedlot cattle
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 DMI variation and selective consumption (sorting) of diets by Nellore cattle. The experiment was designed as a completely randomized block, replicated 12 times, 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 following treatments (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). The DMI variation was calculated for each individual pen as the difference in intake, expressed as % of variation, between consecutive days throughout the study. Samples of orts and diets were collected on days 10 and 40 of the study for particle size distribution determination, which was performed by sieving using the Penn State Particle Size Separator and reported on as-fed basis. Values equal to 1.0 indicate no sorting, <1.0 show selective refusals, and >1.0 indicate preferential consumption. Orthogonal contrasts were used to assess linear, quadratic, cubic and quartic relationship between doses of monensin and the dependent variable. During the period of adaptation, DMI variation was affected (P = 0.02) quadratically as dose of sodium monensin increased (D0: 15.3%; D9: 14.6%; D18: 13.6%; D27: 13.5%; D36: 18.5%); however, the use of different doses of sodium monensin did not affect (P > 0.10) DMI variation during the finishing period. Increasing doses of sodium monensin only affected particle sorting during the adaptation period, in which as dose of sodium monensin increased, sorting for screens one (diagonal opening=19.0 mm; D0=0.986; D9=0.962; D18=0.947; D27=0.928; D36=1.021), two (diagonal opening=8.0 mm; D0=0.992; D9=1.013; D18=1.014; D27=0.936; D36=0.932), and three (diagonal opening=1.18 mm; D0=1.001; D9=1.015; D18=1.065; D27=1.043; D36=0.993), and bottom pan (D0=0.938; D9=1.022; D18=1.020; D27=1.074; D36=1.016) were affected (P < 0.05) quadratically. Thus, the feeding of sodium monensin up to 27 ppm reduced DMI variation, but increased diet sorting during the adaptation period.
Keywords: fluctuation, Nellore, sorting