159. Effects of Dietary Crude Protein Concentration and Urea Source on Nitrogen Utilization in Finishing Nellore Bulls.

IF 3.7 2区农林科学 Q1 AGRICULTURE, DAIRY & ANIMAL SCIENCE

Journal of animal science Pub Date : 2026-09-29 DOI:10.1093/jas/skag272.264

Renato Luís de Paula, Rayane Aparecida A Lino, Gabriela Dias Rezende, Júlia Mara Campos Souza, Javier Martin-Tereso, Isabela P C de Pena Carvalho de Carvalho, Erick D Batista

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Abstract

The objective of this study was to evaluate the effects of dietary crude protein (CP) concentration and urea source on nitrogen (N) utilization in finishing Nellore bulls fed corn-based diets. A total of 84 Nellore bulls (initial body weight = 448 ± 40.5 kg) were assigned to a 2 × 2 factorial arrangement, with treatments allocated across 28 pens (7 pens per treatment; 3 bulls per pen). Treatments consisted of two CP concentrations (11 or 14% of dry matter [DM]) and two urea sources: feed-grade urea (U) or coated urea (CU). Diets were offered as total mixed rations ad libitum twice daily. The CU source contained 82% urea on a DM basis, and in an in vitro assay, 27% of this urea was released in the rumen. The experimental period lasted 90 d. The N intake, fecal and urinary N excretion, and N retention from growth performance were determined to evaluate N utilization efficiency. No CP concentration × urea source interactions were observed (P ≥ 0.31) for N balance variables. Bulls fed diets containing 14% CP had greater N intake compared with those fed diets containing 11% CP (290.6 vs. 222.5 g/d; P < 0.001). Consequently, urinary N excretion was also greater in bulls fed diets containing 14% CP (156.2 vs. 94,8 g/d; P < 0.001). Nitrogen absorption was greater in bulls fed diets containing 14% CP (206.2 vs. 140.2 g/d; P < 0.001). However, reducing dietary CP concentration improved nitrogen utilization efficiency. Bulls fed diets containing 11% CP had greater N retention relative to N intake (20.2 vs. 17.1%; P < 0.001) and greater N retention relative to apparent N absorption (32.2 vs. 24.2%; P < 0.001) compared with bulls fed diets containing 14% CP. Urea source also affected nitrogen losses. Bulls fed diets containing CU had lower fecal N excretion compared with those fed diets containing U (79.2 vs. 87.2 g/d; P = 0.04). In addition, CU increased N retention efficiency relative to N intake compared with U (19.5 vs. 17.9%; P = 0.03). These results indicate that modifying dietary protein concentration and the form of non-protein nitrogen supplementation can influence N partitioning and its overall efficiency in feedlot cattle. In conclusion, reducing dietary CP concentration increased N utilization efficiency by enhancing N retention relative to N intake and absorbed N. In addition, inclusion of coated urea reduced fecal N excretion and increased nitrogen retention efficiency compared to feed-grade urea, demonstrating that these strategies improve N utilization efficiency in finishing cattle. For image description, please refer to the figure legend and surrounding text.

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159. 饲粮粗蛋白质浓度和尿素源对育肥牛氮素利用的影响。

本试验旨在探讨饲粮粗蛋白质（CP）浓度和尿素源对玉米基饲粮育肥牛氮(N)利用的影响。共有84头Nellore公牛（初始体重= 448±40.5 kg）被分配到2 × 2因子安排中，分配到28个栏中（每个处理7个栏，每个栏3头牛）。处理包括两种CP浓度（干物质[DM]的11%或14%）和两种尿素来源：饲料级尿素(U)或包膜尿素（CU）。日粮为全混合口粮，每日2次。以DM为基础，CU源含有82%的尿素，在体外试验中，27%的尿素在瘤胃中释放。试验期90 d。测定饲粮中氮的采食量、粪便和尿氮排泄量以及生长性能引起的氮滞留量，以评价饲粮中氮的利用效率。CP浓度与尿素源之间不存在相互作用（P≥0.31）。饲粮中蛋白质含量为14%的公牛比饲粮中蛋白质含量为11%的公牛摄入更多的氮（290.6 g/d vs 222.5 g/d; P < 0.001）。因此，饲粮中CP含量为14%的公牛尿氮排泄量也更高（156.2对94,8 g/d; P < 0.001）。饲粮中CP含量为14%的公牛对氮的吸收率更高（206.2 g/d vs. 140.2 g/d; P < 0.001）。降低饲粮粗CP浓度可提高氮素利用效率。与饲粮中粗蛋白质含量为14%的公牛相比，饲粮中粗蛋白质含量为11%的公牛相对于氮摄入量有更大的氮保留（20.2比17.1%;P < 0.001），相对于表观氮吸收有更大的氮保留（32.2比24.2%;P < 0.001）。尿素来源也影响氮损失。饲粮中添加CU的公牛粪氮排泄量低于饲粮中添加U的公牛（79.2 g/d vs 87.2 g/d, P = 0.04）。此外，与U相比，CU提高了氮沉积效率（19.5% vs. 17.9%, P = 0.03）。综上所述，调整饲粮蛋白质浓度和非蛋白质氮补充形式可影响饲粮中氮的分配及其整体效率。综上所述，降低饲粮粗蛋白质浓度可通过提高氮沉积（相对于氮摄入和吸收）来提高氮素利用效率。此外，与饲料级尿素相比，包被尿素可减少粪氮排泄，提高氮沉积效率，提高了肥育牛氮素利用效率。有关图像说明，请参阅图例和周围文字。

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来源期刊

Journal of animal science 农林科学-奶制品与动物科学

CiteScore

4.80

自引率

12.10%

发文量

1589

审稿时长

3 months

期刊介绍： The Journal of Animal Science (JAS) is the premier journal for animal science and serves as the leading source of new knowledge and perspective in this area. JAS publishes more than 500 fully reviewed research articles, invited reviews, technical notes, and letters to the editor each year. Articles published in JAS encompass a broad range of research topics in animal production and fundamental aspects of genetics, nutrition, physiology, and preparation and utilization of animal products. Articles typically report research with beef cattle, companion animals, goats, horses, pigs, and sheep; however, studies involving other farm animals, aquatic and wildlife species, and laboratory animal species that address fundamental questions related to livestock and companion animal biology will be considered for publication.