Reynolds Mary Beth, Drewnoski Mary E
Department of Animal Science, University of Nebraska Lincoln, Lincoln, NE 68583-0908, USA.
Transl Anim Sci. 2022 Feb 8;6(1):txac023. doi: 10.1093/tas/txac023. eCollection 2022 Jan.
Annual forages provide a valuable grazing resource for cattle producers; however, annuals are prone to accumulating nitrate and have the potential to cause nitrate toxicity. Although these forages pose a risk of containing high nitrate concentrations, they can be a high-quality feed source. Understanding the factors that affect the potential for toxicity when using these forages is important to help nutritionists and producers make management decisions. This review describes the previous research, current guidelines for nitrate toxicity, and the potential for improvement in our current recommendations. Current extension toxicity guidelines appear to be founded primarily on drenching based studies and overestimate the nitrate toxicity potential of forages. Recommendations need to account for multiple factors that affect the threshold for toxicity. There is evidence that fresh forages have a lower risk of toxicity because of slower release of nitrate into the rumen and a slower rate of dry matter intake. Increased dietary energy and sulfur content reduce the potential for toxicity. Microbial adaptation can reduce the risk and allow use of potentially toxic forages. These factors should influence feeding recommendations. However, there is currently not enough data available to establish new guidelines that account for these main factors. Thus, there is a need for renewed research in this area. The limited number of studies grazing elevated nitrate forages seems to suggest that there is less risk in grazing situations, especially if animals graze selectively. There is a need to develop guidelines for nitrate toxicity and management recommendations when grazing. To accomplish this, there is a need for more studies to evaluate risk of toxicity in grazing situations. These grazing studies need to evaluate the effects of nitrate concentration, forage quality, and grazing management on the potential for nitrate toxicity. While the conservative guidelines that are currently in use reduce risk of nitrate toxicity, they may also cause a significant increase in feed costs for producers.
一年生牧草为养牛户提供了宝贵的放牧资源；然而，一年生牧草容易积累硝酸盐，并有可能导致硝酸盐中毒。尽管这些牧草存在硝酸盐浓度高的风险，但它们可以成为优质的饲料来源。了解使用这些牧草时影响中毒可能性的因素，对于帮助营养学家和养殖户做出管理决策非常重要。本综述描述了以往的研究、当前关于硝酸盐中毒的指导方针，以及我们当前建议中有待改进的地方。目前推广的中毒指导方针似乎主要基于灌服研究，高估了牧草的硝酸盐中毒可能性。建议需要考虑影响中毒阈值的多个因素。有证据表明，新鲜牧草中毒风险较低是因为硝酸盐向瘤胃的释放较慢，干物质摄入量的速率也较慢。增加日粮能量和硫含量可降低中毒可能性。微生物适应可以降低风险，并允许使用潜在有毒的牧草。这些因素应影响饲养建议。然而，目前没有足够的数据来制定考虑这些主要因素的新指导方针。因此，这一领域需要重新开展研究。放牧硝酸盐含量较高的牧草的研究数量有限，似乎表明放牧情况下风险较小，尤其是如果动物进行选择性放牧。需要制定放牧时硝酸盐中毒的指导方针和管理建议。要做到这一点，需要更多的研究来评估放牧情况下的中毒风险。这些放牧研究需要评估硝酸盐浓度、牧草质量和放牧管理对硝酸盐中毒可能性的影响。虽然目前使用的保守指导方针降低了硝酸盐中毒风险，但它们也可能导致养殖户的饲料成本大幅增加。
