GEOGRAPHICAL VARIABILITY OF THE ZINC, MANGANESE AND IRON CONCENTRATIONS OF FORAGES GROWN IN NORTHWESTERN MANITOBA

Abstract

From two or three sites per township (93.24 km2), in the cattle-producing area of Northwestern Manitoba, 612 grass and 271 legume samples were collected and analyzed for zinc (Zn), manganese (Mn) and iron (Fe). Analyses were reported on an air-dry basis of approximately 90% dry matter. Within subregions, the mean Zn concentration ranged from 18.6 to 22.0 mg/kg and the mean Mn concentration ranged from 24.1 to 45.1 mg/kg for grass samples. The mean concentrations for the legume samples ranged from 17.8 to 25.5 mg/kg for Zn and 15.6 and 25.6 mg/kg for Mn. The mean Zn content in the legume samples was 3–5 mg/kg higher (P < 0.05) than that of the grass samples in three of seven subregions. In six of seven subregions the mean Mn content was 5–10 mg/kg higher (P < 0.05) in the grass than the legume samples. The range of Fe concentration was 31.3–1044.5 mg/kg for grass and 29.8–617.2 mg/kg for legume samples. Mean Fe for the entire study area was 107.6 and 93.6 mg/kg for grass and legume samples, respectively. For grazing cattle in Northwestern Manitoba, forages were deficient in Zn and Mn to varying degrees, with excessive intakes of Fe through soil contamination of forages possible. Recommendations for supplemental Zn and Mn should apply to the entire study area, and be based on the difference between the mineral content of forages and the requirement of cattle. Key words: Cattle, forage, minerals, zinc, manganese, iron