Context The Australian government has approved a greenhouse gas (GHG) offset method that requires cattle to consume nitrate in the form of a lick block. Field studies demonstrating the effectiveness of this methodology have not been previously reported. Aims This experiment was conducted to determine the effects on productivity and health when nitrate lick blocks were provided as a supplement to grazing beef cattle. We hypothesised that beef cattle given access to nitrate lick blocks would have similar productivity compared with cattle offered urea lick blocks. Methods Bos indicus breeding cows (n = 76) grazed a 467-ha paddock near Charters Towers, Queensland, between May and November 2014. A two-way remote automatic drafting system enabled allocation of cattle to different treatments while grazing in a common paddock. Treatments were 30% urea lick blocks (30U), or molasses nitrate lick blocks (MNB). At monthly intervals liveweight (LW), body condition score (BCS), and blood methaemoglobin concentration were recorded. Estimates of individual supplement intake were made on three separate occasions using a lithium marker technique. Results Mean daily supplement intake (±s.e.m.) of 30U (122 ± 13 g) was greater (P < 0.001) than MNB (67 ± 8 g). Lesser MNB intake was associated with greater variability for individual supplement intake, a greater proportion of non-consumers of supplement during July (P < 0.05) and reduced voluntary supplement intake until October (P < 0.001). Increasing MNB consumption during October and November was accompanied by elevated blood methaemoglobin concentration (P < 0.001). It was estimated that cattle offered MNB had insufficient supplementary nitrogen intake throughout the study to resolve rumen degradable nitrogen deficiency from grazed forage. Consequently, cattle provided access to MNB demonstrated conceptus free liveweight loss and lesser BCS compared with cattle treated with 30U (P < 0.001). Conclusion Nitrate lick blocks were ineffective as a dual-purpose non-protein nitrogen supplement and methane mitigant for beef cattle grazing poor quality forage. Further field experiments are required to determine if there may be situations where this GHG offset methodology is efficacious. Implications Caution is advised in implementing GHG mitigation methods that involve the use of nitrate lick blocks.

中文翻译：

---

糖蜜硝酸盐舔块对放牧劣质牧草的 Bos indicus 奶牛的补充摄入量、体重、状况评分、血液高铁血红蛋白浓度和畜群规模甲烷排放的影响

背景 澳大利亚政府批准了一种温室气体 (GHG) 抵消方法，该方法要求牛以舔块的形式消耗硝酸盐。以前没有报道过证明这种方法有效性的实地研究。目的 本实验旨在确定当提供硝酸盐舔块作为放牧肉牛的补充剂时对生产力和健康的影响。我们假设，与提供尿素舔块的牛相比，获得硝酸盐舔块的肉牛具有相似的生产力。方法 2014 年 5 月至 11 月期间，白种牛（Bos indicus）种牛（n = 76）在昆士兰查特塔附近的 467 公顷围场放牧。双向远程自动牵牛系统能够在公共围场放牧时将牛分配到不同的处理方式。处理为 30% 尿素舔块 (30U) 或糖浆硝酸盐舔块 (MNB)。每隔一个月记录一次活重 (LW)、身体状况评分 (BCS) 和血液高铁血红蛋白浓度。使用锂标记技术在三个不同的场合对个体补充剂摄入量进行了估计。结果 30U (122 ± 13 g) 的平均每日补充摄入量 (±sem) 比 MNB (67 ± 8 g) 大 (P < 0.001)。较少的 MNB 摄入量与个体补充剂摄入量的更大可变性、7 月份非消费者补充剂的比例更大 (P < 0.05) 和 10 月之前自愿补充剂摄入量减少 (P < 0.001) 相关。10 月和 11 月期间 MNB 消费量的增加伴随着血液高铁血红蛋白浓度的升高（P < 0.001）。据估计，在整个研究过程中，提供 MNB 的牛没有足够的补充氮摄入来解决来自放牧草料的瘤胃可降解氮缺乏。因此，与用 30U 处理的牛相比，使用 MNB 的牛证明了无概念活重损失和更小的 BCS（P < 0.001）。结论 硝酸盐舔块作为两用非蛋白氮补充剂和甲烷缓释剂对放牧劣质牧草的肉牛无效。需要进一步的现场实验来确定是否存在这种温室气体抵消方法有效的情况。影响 在实施涉及使用硝酸盐舔块的温室气体减排方法时，建议谨慎行事。