Effect of controlled-release of nitrogen on fermentation and in situ digestibility of Cynodon dactylon

Objective. To evaluate the effect of a controlled-release non protein nitrogen source (CRNpn) on some parameters of rumen fermentation and in situ digestibility of Cynodon dactylon. Materials and methods. Four rumen fistulated cows fed a basal diet with Cynodon dactylon hay (4.8% crude protein and 78.4% neutral detergent fiber), 1 kg sugar cane molasses and 55 g mineral mix (Control), and experimental treatment plus 150 g urea (Urea), replaced Urea with CRNpn by 50% of the nitrogen contribution (Urea/CRNpn) and 183 g CRNpn (CRNpn), in a 4x4 Latin Square with periods of 17 days. Intake was measured between days 7 and 14, serial rumen content samples were taken to measure pH, ammonia nitrogen (N-NH3) and volatile fatty acids on day 15. Organic matter (OMD48) and neutral detergent fiber (NDF48) digestibility were measured with nylon bags at 48 h. Results. No differences (p>0.05) on dry matter intake (8.2±0.35 kgDM/animal/day), ruminal pH (6.1±0.21), OMD48 (52.2±6.2%) and NDF48 (30.1±2.8%) were observed. However, there were differences (p<0.01) in N-NH3 daily averages (19.1, 166.7, 181.6 and 281.8 mg/L; respectively). CRNpn increased (p<0.05) the propionic acid (27.3%), reduced T1/2 (13.2%) and optimized the P:E relation (22.0±0.76). Conclusions. The use of a CRNpn source generated a volatile fatty acid profile with gluconeogenic pattern, optimized the N-NH3 concentration and improved the P:E relation, and therefore may be considered as an alternative to manipulate the ruminal environment of cattle fed with fibrous resources.