Evaluation of nitrate and prussic-acid risk in annual forages submitted by producers to a commercial forage testing laboratory in Nebraska

Objective

My objective was to determine whether there is a relationship between nitrate (NO₃-N) toxicity risk and prussic-acid (HCN) toxicity risk in annual forages for grazing livestock.

Materials and Methods

Throughout the grazing seasons in 2021, 2022, and 2023, livestock producers submitted annual forages known for accumulating both NO₃-N and HCN to Ward Laboratories Inc. (Kearney, NE). Properly submitted samples were tested for both NO₃-N and HCN (n = 201). Regression analysis and ANOVA were performed. Additionally, samples were broken down by “risk of toxicity” to determine whether risk of ruminant animal health issues was related to NO₃-N and HCN.

Results and Discussion

Average NO₃-N concentration was not statistically significantly different by forage specie group; however millet was lower in HCN compared with other forage species. Samples submitted in November were lower in NO₃-N than samples submitted in August, September, and October (Figure 2). However, there was no statistical difference in HCN concentration based on the month samples were submitted. The concentrations of NO₃-N and HCN were not correlated (R² <0.01). Additionally, samples categorized as safe for NO₃-N were not consistently categorized as safe for HCN and vice versa.

Implications and Applications

A low concentration of HCN or NO₃-N in a forage does not imply a low concentration of the other. Therefore, forages likely to accumulate these toxic substances should be analyzed for both NO₃-N and HCN before grazing to help mitigate health risks for ruminant animals.