August 15, 2025

Impact of supplementing different sources of non-protein nitrogen on ruminal fermentation, nutrient digestibility, and microbial protein synthesis in beef cattle consuming a corn silage-based diet.

Key Points

Steers supplemented with urea-biuret consumed more dry matter than those with urea-biuret-nitrate, indicating a preference for certain non-protein nitrogen sources.
Animals consuming urea-biuret-nitrate digested more acid detergent fiber, highlighting differences in nutrient digestibility among treatments.
Rumen fermentation metrics like microbial N flow were consistent, showing minimal variation among non-protein nitrogen treatments.
Lower ammonia concentration was observed in steers supplemented with urea-biuret-nitrate compared to other treatments, suggesting a potential benefit for rumen health.

Abstract

Supplementation of low-protein diets with non-protein nitrogen (NPN) increases ruminal degradable protein and improves rumen fermentation and microbial growth. The objective of this experiment was to evaluate the effect of supplementing urea-biuret (UB) and urea-biuret-nitrate (UBN) mixtures relative to urea (U) on rumen fermentation and microbial N outflow in growing steers. Twelve American Aberdeen steers were used in a replicated and balanced 3 × 3 Latin square design (LSD) with three periods of 35 days each. Steers were housed in pens and consumed a corn silage-based diet. Steers were stratified by body weight and randomly allocated to one of the three NPN supplementation treatments. Treatments were supplementation with U, UB, and UBN, adjusted to the amount of N provided by U when included at 1% of the diet on a dry matter (DM) basis. Intake and feeding behavior were individually recorded throughout the experiment. In each period, steers were adapted to increasing levels of NPN during the first 8 days. From day 19 to 23, feed and fecal samples were collected to assess nutrient digestibility. Samples of blood, rumen contents, and omasal digesta were collected on d 20 to 23. On d 24, rumen evacuation was performed and subsequently steers were dosed with Co-EDTA and YbCl3 to determine the passage rate of digesta flow. Rumen fluid collection was conducted on d 24 and 25. Steers did not receive NPN supplementation from day 26 to 35 during the washout period. Microbial N flow was estimated for each animal within periods. Intake, digestibility, digesta flow, and microbial N flow were analyzed using a 3 × 3 LSD, while blood and rumen fermentation parameters were analyzed using a 3 × 3 LSD with repeated measures. Steers supplemented with UB tended (P 0.10) among NPN-supplemented treatments. Steers supplemented with UBN showed lesser (P < 0.05) concentration of ammonia than those with U and UB. In conclusion, novel NPN mixtures have the potential to modify ruminal fermentation without affecting microbial protein outflow.

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