Use of Virginiamycin to shorten the adaptation period to high-energy diets and to increase carcass weight of feedlot Nellore cattle.

Abstract

The objectives of this project will be as follows: 1) investigate shorter periods of adaptation to high-concentrate diets when only Virginiamycin (VM) is fed as feed additive (studies 1 and 3); and 2) evaluate the effects of feeding a diet containing a higher proportion of concentrate in the last 40 days of the finishing period supplemented either with VM or sodium monensin (MON) to increase carcass weight (study 2) of feedlot Nellore cattle. In this project, three studies are proposed: in the studies 1 and 3, the treatments will be as follows: 1) MON (30 mg/kg) and adaptation period of 14 days; 2) MON (30 mg/kg) + VM (25 mg/kg) and adaptation period of 14 days; 3) VM (25 mg/kg) and adaptation period of 14 days; 4) VM (25 mg/kg) and adaptation period of 9 days; and 5) VM (25 mg/kg) and adaptation period of 6 days. In the study 2, the treatments will be as follows: 1) MON (30 mg/kg) for the entire feeding period and 14 days of adaptation; 2) VM (25 mg/kg) for the entire feeding period and 6 or 9 or 14 days of adaptation (based on the results of study 1); 3) VM (25 mg/kg) + MON (30 mg/kg) during the period of 14 days of adaptation and only VM (25 mg/kg) in the finishing period; 4) VM (25 mg/kg) + MON (30 mg) for the entire feeding period and 14 days of adaptation; and 5) VM (25 mg/kg) + MON (30 mg/kg) during the 14 days of adaptation and up to 72 days on feed, and only VM (25 mg/kg) from day 73 to day 112 on feed. In the studies 1 and 2 will be evaluated variables of feedlot performance, carcass traits, feeding behavior, and rumen and cecal morphometrics of 210 Nellore yearling bulls (120 and 90 for the studies 1 and 2, respectively). In the study 3, it will be used 5 Nellore bulls cannulated in the rumen in a 5 x 5 Latin square, where the following response variables will be evaluated: rumen fermentation patterns, such as pH, short-chain fatty acids, as well as determination of ciliated protozoa and nutrients digestibility. (AU)