Effects of tannins and monensin on the modulation of in vitro ruminal fermentation and ammonia production of nitrogen‐fertilized and non‐fertilized Urochloa brizantha cv. Marandu

Abstract

AbstractThis study was conducted to evaluate the effects of the increasing levels of tannin supplementation—0 (control—no additive), 2, 4 and 6 mg/g of dry matter (DM)—versus monensin (0.02 mg/g DM) on in vitro ruminal fermentation of either nitrogen (N)‐fertilized or non‐fertilized Urochloa brizantha cv. Marandu. Ruminal fluid was obtained from two grazing Nellore bulls receiving 0.3% of the body weight of a supplement free of additives. The incubations were conducted for four consecutive weeks with gas production (GP) recorded up to 96 hr, whereas pH and ruminal ammonia (N‐NH3) were measured at 24 and 48 hr, and volatile fatty acids at 48 hr. Additionally, in vitro dry matter digestibility (IVDMD) and in vitro neutral detergent fiber digestibility (IVNDFD) were measured at 24, 48 and 96 hr. The crude protein (CP) contents for N‐fertilized and non‐fertilized forages were 11.77% and 7.75, respectively. There was no interaction between forage and additives (p > 0.05) for fermentation kinetic parameters. Nitrogen fertilization reduced (p < 0.05) the theoretical maximum of gas production (ml) (a), the maximum gas production rate (ml/hr) (b) and the lag time (L). The inclusion of monensin reduced (p < 0.05) b and L compared with control and inclusion of tannin. In general, the inclusion of monensin and tannins reduced (p < 0.05) the IVDMD and IVNDFD. Compared to monensin, tannin reduced (p < 0.05) the N‐NH3 and the acetate:propionate ratio. The use of N fertilization in tropical forage reduces in vitro gas production. Tannins and monensin influence the modulation of ruminal fermentation mainly by reducing neutral detergent fiber (NDF) digestibility. Tannins reduce N‐NH3 concentration regardless of the use of N fertilization of Urochloa brizantha cv. Marandu.