Mary E. Drewnoski
Date of this Version
Lenz, Mary E., Risk of Nitrate Toxicity when Grazing Annual Forages. 2018. M.S. Thesis Univ. of Nebraska- Lincoln.
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. 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. An additional study was done to understand how the nutritive value of late-summer planted brassicas and small grains change through early winter. Even after the forage froze and was brown in January, these forages remained a highly digestible feed source, indicating producers can increase yields by delaying grazing in the fall, and still utilize the forage in the winter.
Advisor: Mary E. Drewnoski