Evaluating nitrate toxicity potential in grazed cover crops

Project Overview

Project Type: Graduate Student
Funds awarded in 2017: $11,947.00
Projected End Date: 08/31/2019
Grant Recipient: University of Nebraska — Lincoln
Region: North Central
State: Nebraska
Graduate Student:
Faculty Advisor:
Dr. Mary Drewnoski
University of Nebraska - Lincoln

Information Products


  • Animals: bovine


  • Animal Production: animal protection and health
  • Crop Production: cover crops


    Annual forages provide a valuable grazing resource for producers; however, annuals are prone to accumulating nitrate and toxicity can be a potential challenge. There are multiple publications regarding nitrate toxicity, but few, if any, address grazing high nitrate forages. There is variability on what amount of nitrate is considered toxic to cattle, and information is not available on the frequency producers experience toxicity when feeding annual forages. A literature review provided insight to how the guidelines on nitrate toxicity were established. The guidelines on nitrate toxicity used today are very similar to what was established in the 1940’s and 1960’s when researchers used nitrate salts to determine the toxic dose. Multiple factors impact the risk of nitrate toxicity in individual scenarios and indicate that the risk of nitrate toxicity when grazing annual forages is less than the risk when feeding hayed annual forages. To better understand the risk when grazing forages, cooperating beef producers were contacted and blood and forage samples were taken to observe how affected cattle were while grazing various concentrations of nitrate. To understand the incidence of nitrate toxicity in the North Central Region of the U.S., a survey was distributed through the “UNL BeefWatch” newsletter to producers. Though producers appeared concerned about nitrates in annual forages, only 38% have experienced an issue. Management decisions to test annual forages for nitrates did not change if a producer had previously experienced toxicity. Producers tended to experience nitrate toxicity more often when grazing (31%) compared to feeding hay (21%). This data agreed with a dataset of samples submitted to Ward Laboratories, in which 48% of fresh brassica samples, 23% of fresh annual grasses, and 5% of dry annual grasses analyzed would have been considered at risk for causing toxicity. However, the increased incidence of toxicity in pasture is smaller than expected based on the large proportion of fresh forages sampled and submitted to the commercial laboratory and considered toxic. Some mitigation factors may explain differences in toxicity risk for animals grazing compared to animals fed annual forage hay. Understanding these factors and the cost of not utilizing the forage is important for management decisions. Although these forages pose a risk of toxicity, they provide a high quality feed source.

    Project objectives:

    Grazing cover crops can be an avenue to obtain economic value while achieving environmental stewardship. This project addresses one of the potential barriers to grazing cover crops as high nitrates levels have been observed in the forage species used. However, the perceived risk when grazing cover crops/annual forages may be greater than actual risk. The reduced rate of intake and increased selectivity when grazing, the decreased rate of nitrate release into the rumen with fresh forages, and the high-energy content of the diet may decrease the potential for toxicity.

    The objective of this project was to: Increase the understanding of nitrate toxicity potential in grazed cover crops/annual forages.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.