A Phytogenic Feed Additive Improves Performance By Nellore Growing Bulls Grazing on Tropical Pastures

Abstract Our objective was to evaluate the effect of including a phytogenic additive in protein supplement on performance of grazing Nellore bulls during growing phase in the rainy season. One hundred and fourteen animals (iBW, 273 ± 4.46 kg) were allocated for 152 days in six paddocks of Brachiaria brizantha cv. Marandu (~7 ha each), with automatic feeders and scales (in drinkers, Intergado, Brazil); and randomly distributed in six treatments fed on protein supplement (30% Crude protein): 1) Negative Control (CON), with no additive; 2) Monensin (MON; positive control, 15 ppm) 3) Digestarom (DSM Nutritional Products) at 0.2 g· animal-1· /day-1 (D0.2); 4) Digestarom at 0.4 g· animal-1· /day-1 (D0.4); 5) Digestarom at 0.6 g· animal-1· /day-1 (D0.6) and 6) Digestarom at 0.8 g· animal-1· /day-1 (D0.8). Supplement offered and additives inclusion were adjusted weekly, based on the intake of the previous week. Supplement intake (SI, measured by the automatic feeders) and Average Daily Gain (ADGs; measured subtracting final and initial fast BW, divided by 152 days; and ADGf; measured by the automatic scales) were evaluated during this study. Data were analyzed by SAS PROC GLIMMIX and significance of 5% was adopted. Means of Digestarom levels were compared with the CON and MON, and of the MON was compared with the CON using a Dunnett test. MON reduced (P < 0.05) SI (175 g/d) compared with CON (433 g/d) and all Digestarom levels (423, 303, 468 and 332 g/d respectively). D0.4 and D0.8 also reduced SI when compared with CON. The ADGs and the ADGf of animals on D0.6 (927 and 1.262 g/d) were greater (P < 0.05) compared with CON (0.860 and 1.127 g/d) and MON (0.840 and 1.114 g/d). The other levels of Digestarom [D0.2 (0.886 and 1.107 g/d), D0.4 (0.823 and 1.054 g/d), and D0.8 (0.853 and 1.071 g/d)] did not differ from CON and MON. D0.6 did not reduce SI (compared with CON; P > 0.05) and increased ADGs and ADGf (compared with CON and MON; P < 0.05). Feeding Digestarom at the dose of 0.6 g· animal-1· /day-1 may increase BW gain of grazing growing bulls during rainy season.