Ruminal fermentation standard and use of nutrients by nelore beef confined supplemented with virginiamycin and / or monensine

The objective of this study was to evaluate the ruminal fermentation pattern, protozoa counts, ruminal degradability of nutrients, rumen solids disappearance rate, feeding behavior and particle sorting of cannulated Nellore cattle fed with different combinations of sodium monensin (MON) and virginiamycin (VM) during adaptation and finishing periods in the feedlot. Five 5x5 Latin square rumen-fistulated Nellore cattle were used, where each period consisted of 28 days + 7 washout, with the following treatments: T1 - MON (30 mg / kg); T2 - MV (25 mg / kg); T3 - MV (25 mg / kg) + MON (30 mg / kg) during the adaptation period and MV only (25 mg / kg) during termination; T4 - VM (25 mg / kg) + MON (30 mg); and T5 - MV (25 mg / kg) + MON (30 mg / kg) during adaptation and termination 1, and MV only (25 mg / kg) during termination 2. The adaptation period was 14 days for all treatments. The variables evaluated in this study were: ruminal degradability of DM, starch and CP; ingestive behavior and particle selection; rumen pH, temperature and oxy-redox potential via data logger; number of protozoa; molar ratio of short chain fatty acids, as well as lactate and ammonia concentrations and solids disappearance rate. During the adaptation and termination 1 phase, T2 presented higher IMS. In termination 1 phase, T3 can exceed the IMS of treatment T1. Arriving at termination 2 phase, T3 reached IMS of T2 and exceeded that of T5. It was also observed that T1 and T4 presented lower solids passage rate in kg/h compared to T2 and T3. T3 also showed higher potential degradability of DM during termination 1 phase, compared to T2, T4 and T5, and greater effective starch degradability, at levels of 2, 5 and 8%, when compared to T4 and T5 during finishing phase 2. There was no significant difference between treatments for total SCFA. Therefore, removing MON at the end of finishing 1 does not affect the ruminal fermentation and nutrient utilization pattern of cannulated Nellore cattle, but the removal of MON at the end of adaptation causes changes in the fermentative pattern and nutrient utilization, which persisted until finishing phase 2. (AU)