LAUSR

BACKGROUND Two consecutive trials were carried out to study the effects of dietary supplementation of rumen protected methionine (RPM) on nutrient digestibility, nitrogen (N) metabolism (Trial 1), and consequently the nitrous oxide (N2 O) emissions of urine in beef cattle (Trial 2). Eight 24-month old castrated Simmental bulls with liveweight of 494 ± 28 kg and four levels of dietary supplementation of RPM at 0, 10, 20 and 30 g head-1 ·d-1 were allocated in a replicated 4 × 4 Latin square for Trial 1 and the N2 O emissions of the urine samples collected in Trial 1 were measured using static incubation technique in Trial 2. RESULTS Supplementation of RPM at 0, 10, 20 and 30 g head-1 ·d-1 to basal ration deficient in methionine (Met) did not affect the apparent digestibility of dry matter, organic matter, neutral detergent fibre or acid detergent fibre (P > 0.05), but decreased the urinary excretions of total N (P < 0.05) and urea (P < 0.001), increased the ratio of N retention/digested N (P < 0.05) in beef cattle, and decreased the estimated cattle urine N2 O-N emissions by 19.5%, 23.4% and 32.6%, respectively (P < 0.001). CONCLUSION Supplementation of RPM to Met-deficient ration is effective to improve the utilization rate of dietary nitrogen and decrease the N2 O emissions of urine in beef cattle. This article is protected by copyright. All rights reserved.