Vargas Juan de J, Tarnonsky Federico, Maderal Araceli, Podversich Federico, Fernández-Marenchino Ignacio, Cuervo Wilmer, Ramirez Vanesa, Novo Sabina, Fernández-Lehmann Andrés, Ruiz-Moreno Martín, Schulmeister Tessa M, Ruiz-Ascacibar Isabel, Ipharraguerre Ignacio R, DiLorenzo Nicolás
Department of Animal Sciences, North Florida Research and Education Center, IFAS, University of Florida, Marianna, FL, USA32446.
AgNext, Department of Animal Sciences, Colorado State University, Fort Collins, CO 80523, USA.
J Anim Sci. 2025 Jan 4;103. doi: 10.1093/jas/skaf272.
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 3 periods of 35 d each. Steers were housed in pens and consumed a corn silage-based diet. Steers were stratified by body weight and randomly allocated to 1 of the 3 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 days 19 to 23, feed and fecal samples were collected to assess nutrient digestibility. Samples of blood, rumen contents, and omasal digesta were collected on days 20 to 23. On day 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 days 24 and 25. Steers did not receive NPN supplementation from days 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 < 0.07) to consume more DM and organic matter (OM) than those supplemented with UBN; however, animals supplemented with UBN tended (P = 0.051) to digest more acid detergent fiber in the total tract. Steers supplemented with U and UB showed greater (P < 0.05) DM and OM flow throughout the omasum than those with UBN. Microbial N flow, microbial efficiency, and the concentration of total volatile fatty acids were not different (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.
用非蛋白氮（NPN）补充低蛋白日粮可增加瘤胃可降解蛋白，并改善瘤胃发酵和微生物生长。本试验的目的是评估相对于尿素（U），补充尿素 - 缩二脲（UB）和尿素 - 缩二脲 - 硝酸盐（UBN）混合物对生长公牛瘤胃发酵和微生物氮流出的影响。12头美国阿伯丁公牛用于重复平衡的3×3拉丁方设计（LSD），共3个阶段，每个阶段35天。公牛饲养在围栏中，采食以玉米青贮为基础的日粮。根据体重对公牛进行分层，并随机分配到3种NPN补充处理中的1种。处理方式为分别补充U、UB和UBN，当以干物质（DM）计占日粮的1%时，将其调整为与U提供的氮量相同。在整个实验过程中，单独记录采食量和采食行为。在每个阶段的前8天，使公牛适应逐渐增加的NPN水平。从第19天到第23天，采集饲料和粪便样本以评估养分消化率。在第20天到23天采集血液、瘤胃内容物和网胃消化物样本。在第24天，进行瘤胃排空，随后给公牛投喂Co - EDTA和YbCl3以确定消化物流动的通过率。在第24天和25天进行瘤胃液采集。在洗脱期的第26天到35天，公牛不接受NPN补充。对每个阶段内的每头动物估计微生物氮流量。采食量、消化率、消化物流动和微生物氮流量采用3×3 LSD进行分析，而血液和瘤胃发酵参数采用具有重复测量值的3×3 LSD进行分析。补充UB的公牛比补充UBN的公牛有采食更多干物质（DM）和有机物（OM）的趋势（P < 0.07）；然而，补充UBN的动物在全消化道中消化更多酸性洗涤纤维的趋势（P = 0.051）。补充U和UB的公牛在整个网胃中的DM和OM流量比补充UBN的公牛更大（P < 0.05）。在补充NPN的处理之间，微生物氮流量、微生物效率和总挥发性脂肪酸浓度没有差异（P > 0.10）。补充UBN的公牛比补充U和UB的公牛氨浓度更低（P < 0.05）。总之，新型NPN混合物有潜力改变瘤胃发酵而不影响微生物蛋白流出。
