Microscopic variables of rumen epithelium of feedlot Nellore cattle submitted to different nutritional strategies using sodium monensin and virginiamycin

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, 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), on the histological variables of feedlot Nellore cattle. In this project there will be two experiments. In study 1 the treatments will be: 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 study 2, the treatments will be: 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 finishing period 1, and only VM (25 mg/kg) during the finishing period 2. It will be used 120 Nellore bulls, with average initial body weight of 370 kg. After the slaughter, the rumen of all animals will be emptied and washed, and will be collected rumen epithelium samples from the ventral sac of each animal. Afterwards, it will be determined the height, width, and area of ruminal papillae, as well as mitotic index related to the nuclei of the basal layer, and layer thickness of keratin of the epithelium. (AU)