Fadul-Pacheco L, Pellerin D, Chouinard P Y, Wattiaux M A, Duplessis M, Charbonneau É
Département des Sciences Animales, Université Laval, Québec, QC, Canada G1V 0A6.
Department of Dairy Science, University of Wisconsin, Madison 53706.
J Dairy Sci. 2017 Aug;100(8):6592-6601. doi: 10.3168/jds.2016-11788. Epub 2017 Jun 7.
Nitrogen efficiency (milk N/dietary N; NE) can be used as a tool for the nutritional, economic, and environmental management of dairy farms. The aim of this study was to identify the characteristics of herds with varying NE and assess the effect on farm profitability. One hundred dairy herds located in Québec, Canada, comprising on average 42 ± 18 cows in lactation were visited from October 2014 to June 2015. Feed intake was measured over 24 h. Samples of each feedstuff were taken and sent to a commercial laboratory for analysis of chemical composition. Feeding management and feed prices were recorded. Milk yield was recorded and milk samples were collected over 2 consecutive milkings. Fat, protein, and milk urea N were analyzed. Balances of metabolizable protein (MP; MP supply - MP requirements) and rumen degradable protein (RDP; RDP supply - RDP requirement) were calculated. A hierarchical cluster analysis was conducted and allowed grouping the farms by their NE. Four clusters were identified with an average NE of 22.1 (NE22), 26.9 (NE27), 30.0 (NE30), and 35.8% (NE36). Herds in clusters NE30 and NE36 were fed diets with greater concentrations of starch, net energy for lactation, and nonfiber carbohydrates than those in the other 2 clusters. Moreover, the average proportion of corn silage was lower for herds in cluster NE22 compared with NE30 and NE36 (8.23 vs. 31.8 and 31.3% of total forages, respectively). In addition, crude protein of the diets declined from an average of 16.0 to 14.9% with increasing NE among clusters. Average dry matter intake declined from 26.1 to 22.5 kg/d as NE of clusters increased. Herds in cluster NE22 had lower yields of milk (28.7 vs. 31.8 kg/d), fat (1.15 vs. 1.29 kg/d), and protein (0.94 vs. 1.05 kg/d) than the other clusters. Also, milk urea N was greater for farms in cluster NE22 (13.2 mg/dL) than for farms in the other clusters (11.4 mg/dL). Furthermore, MP and RDP balances decreased from 263.2 to -153.7 g/d and from 594.7 to 486.9 g/d, respectively, with increasing NE among clusters. Income over feed cost increased from $14.3 to $17.3/cow per day (Can$) as NE among clusters augmented. Results from this study showed that some farms were able to achieve high NE by using lower levels of dietary N and having cows with lower DMI while maintaining milk performance. These farms had a potentially lower environmental impact, and they were more profitable.
氮效率（牛奶氮/日粮氮；NE）可作为奶牛场营养、经济和环境管理的一种工具。本研究的目的是确定不同氮效率牛群的特征，并评估其对农场盈利能力的影响。2014年10月至2015年6月期间，对加拿大魁北克的100个奶牛群进行了走访，这些牛群平均有42±18头泌乳奶牛。测量了24小时的采食量。采集每种饲料的样本并送往商业实验室分析化学成分。记录饲养管理和饲料价格。记录产奶量，并在连续两次挤奶时采集牛奶样本。分析了脂肪、蛋白质和牛奶尿素氮。计算了可代谢蛋白质（MP；MP供给 - MP需求）和瘤胃可降解蛋白质（RDP；RDP供给 - RDP需求）的平衡。进行了层次聚类分析，可根据氮效率对农场进行分组。确定了四个聚类，平均氮效率分别为22.1%（NE22）、26.9%（NE27）、30.0%（NE30）和35.8%（NE36）。与其他两个聚类相比，NE30和NE36聚类中的牛群所喂日粮中淀粉、泌乳净能和非纤维碳水化合物的浓度更高。此外，与NE30和NE36相比，NE22聚类中牛群的玉米青贮平均比例更低（分别占总饲草的8.23%、31.8%和31.3%）。此外，随着聚类中氮效率的提高，日粮粗蛋白从平均16.0%降至14.9%。随着聚类氮效率的增加，平均干物质采食量从26.1千克/天降至22.5千克/天。NE22聚类中的牛群产奶量（28.7千克/天对31.8千克/天）、脂肪（1.15千克/天对1.29千克/天）和蛋白质（0.94千克/天对1.05千克/天）均低于其他聚类。而且，NE22聚类中农场的牛奶尿素氮（13.2毫克/分升）高于其他聚类中的农场（11.4毫克/分升）。此外，随着聚类中氮效率的增加，MP和RDP平衡分别从263.2克/天降至 - 153.7克/天和从594.7克/天降至486.9克/天。随着聚类中氮效率的提高，每头奶牛每天的饲料成本收益从14.3加元增加到17.3加元。本研究结果表明，一些农场能够通过使用较低水平的日粮氮并使奶牛采食量降低同时维持产奶性能来实现高氮效率。这些农场对环境的潜在影响较小，并且更具盈利能力。
