PSXIII-15 Effects of a phytogenic feed additive on ruminal fermentation parameters in grazing beef cattle.

Abstract Our goal was to evaluate the effect of a phytogenic additive (Digestarom® Prime, dsm-firmenich, Switzerland) on ruminal fermentation of beef cattle grazing tropical pastures during the raining season. Six Nellore young bulls previously fistulated in the rumen were kept in the same paddock (2.2 ha), with B. Brizantha cv. Marandú, equipped with electronic feeders that provided individual access (Intergado® System), from December to March. The experiment was conducted in a 3x3 Latin square design duplicated simultaneously. The treatments consisted of a basal mineral supplement, with the inclusion of Digestarom® in doses adjusted to 0.4 g/animal/day (D04) or 0.6 g/animal/day (D06) or of Monensin (Mon; 15 ppm). Animals were weighed at the beginning of each experimental period to adjust the amount of supplement provided. In each experimental period, 13 days were allowed for adaptation to the treatment and, on the 14th day of each period, ruminal fluid was collected from the animals at 07:00, 12:00, 19:00 and 00:00 hours for subsequent analysis of volatile fatty acids (VFA), ammonia, and microbial protein. The data was analyzed using Proc Glimmix on SAS on Demand, adopting a significance level of 5%. There was an interaction between time and treatment for VFA, acetate, butyrate and propionate (P< 0.05). Overall, the pattern of VFA production was similar for animals on D06 and Mon, with peak of VFA production, acetate, propionate and butyrate at 19:00, while animals receiving D04 presented a peak on VFA production at 00:00. Average total VFA production was 166 mmol/L for Mon, 175 mmol/L for D04 and 167 mmol/L for D06. There was an effect of time of collection on ammonia production (P< 0.05), with all treatments presenting the highest ammonia production at 19:00, but no effect of treatment was observed (P >0.05). Average ammonia production was 39.4 mg/dL for Mon, 48.5 mg/dL for D04 and 48,3 mg/dL for D06. Interaction of time and treatment was also observed for microbial protein (P< 0.05), with average microbial protein production of 327 µg/mL for Mon, 343 for D04 and 317 µg/mL for D06. In conclusion, Digestarom® at dose of 0.6 g/animal/day provides a pattern of ruminal fermentation similar to monensin for grazing beef cattle.