The majority of research on nitrate in ruminant diets has been focused on its toxic role in
the animal. Since nitrate is the major precursor of nitrogenous compounds in plants including
protein, it is safe to assume that under grazing conditions where pastures are growing that
ruminants would ingest some nitrate on a continuous basis. This varies from very small amounts
to the large concentrations that under certain conditions are known to become toxic (see values in
Table 1). O’Donovan and Conway (1968) in Ireland showed that with high rates of application of
nitrogen fertilizers that crude protein in the pasture sometimes exceeded 6% N (3.9-6.4%) with up
to 45% (from 5-45%) as nitrate –N. Recent work by Lovett et al (2004) found that for each 1%
increase in crude protein (from 13-23%CP) in perennial rye grass from N fertilizer application to
the soil, nitrate in forage increased linearly by 0.035g/kg dry matter (from 0.04 to 3.6 g/kg DM)
with an R2 of 0.94. The point being made is that nitrate is not an uncommon substrate in rumen