The effects on ewes and lambs of grazing pasture containing differing levels of nitrate‐nitrogen

Perennial ryegrass (Lolium perenne) swards were given annual applications in six equal instalments at 21‐day intervals of either 100, 400 or 700 kg ha⁻¹ N in 1973 and 1974. Ewes with twin lambs were rotationally grazed on these areas. The nitrate‐N content of the grass was measured immediately before grazing. Blood samples were taken at regular intervals from the ewes and lambs to estimate blood methaemoglobin and certain plasma mineral concentrations. A maximum nitrate‐N concentration of of 0.67% in the herbage dry matter was recorded but no adverse effect of N fertilizer was found in terms of the blood constituents or growth of the sheep, or in the carcase quality of the lambs.