Feeding Behavior of Nellore Cattle Supplemented with Different Combinations of Sodium Monensin and Virginiamycin

This study, conducted at Sao Paulo University feedlot, in Botucatu Campus, Brazil, was designed to evaluate the effect of combined use of monensin (MON) and virginiamycin (VM) during the adaptation period and finishing period on feeding behavior of Nellore cattle. Seventy-two 26-mo-old yearling Nellore bulls (388±31.07kg), backgrounded on pasture were randomly allocated and kept in 24 pens (10 m² and 1.67m bunk space per animal) according to the treatments: MON (30 mg/kg) during the adaptation and finishing period, MON (30mg/kg)+VM (25mg/kg) during the adaptation and only VM (25mg/kg) in finishing, MON (30mg/kg)+VM (25mg/kg) during the adaptation and finishing period, and only VM (25mg/kg) during the adaptation period and MON (30 mg/kg)+VM (25mg/kg) during the finishing period, thus characterizing a completely randomized block design. Each treatment was composed of 6 replications (pens) in this study. The adaptation program consisted of ad libitum feeding of 3 adaptation diets overa period of 19 d with the concentration level increasing from 69% to 84% of diet DM. Cattle were fed twice daily for ad libitum consumption throughout the study. Two visual appraisals were conducted, 1 at the end of the adaptation period and another at d 60 of the experimental period, every 5 min during 24 h at each observation. At the end of the adaptation period no treatment effects were observed for the time spent resting, ruminating and eating as well as the length and the number of meals per day. Cattle supplemented only with VM during the adaptation period and MON plus VM in the finishing period and those supplemented with MON plus VM during the adaptation period and only VM in the finishing period showed greater (P<0.05) DMI (8.15; 8.10 vs. 6.99), eating a rate of DM (20.11; 21.20 vs 26.9, min/kg of DM) and eating a rate of NDF (79.69; 91.39 vs 112.52, min/kg of NDF) compared to those fed only by MON during both adaptation and finishing period. However, at the 60thd of experiment cattle fed with the combination of MON and VM during the adaptation period and only VM during the finishing period showed greater DMI (P=0.01), eating a rate of DM (P<0.01) and NDF (P<0.01) compared to all other treatments. Supplementation with different combination of MON and VM change feeding behavior of Nellore cattle, nevertheless, supplementation with MON and VM during the adaptation period and only VM in finishing period seem to improve the feeding behavior traits of Nellore cattle.