COPPER TO MOLYBDENUM RATIO AND MOLYBDENUM AND COPPER CONCENTRATIONS IN RUMINANT FEEDS

Abstract

Molybdenum and Cu concentrations and Cu/Mo ratios were determined on samples of legume hay, grass legume hay, grass hay, sedge hay, oat forage, corn silage and grains throughout British Columbia. In addition, the relationships between Cu distribution and both Mo concentration and the Cu/Mo ratio were determined for all feeds. The critical Cu/Mo ratio was selected as 2.0, and samples with ratios below 2.0 would be expected to cause conditioned copper deficiency. Sedge hays had a mean Cu/Mo ratio of 2.1, which was less than half the mean ratio of 4.4 for grass hays. The mean ratios for the other classes of feed were 5.0 or higher. Notwithstanding the favorable mean ratios, 19% of all samples had ratios below 2.0. The lowest Cu/Mo ratio was 0.1 and the highest was 52.7, which shows extreme variability. Molybdenum concentrations were generally low, with 35% of all samples below 1 ppm Mo. There were no unusually high Mo concentrations, as only 1% of all feeds were above 8.0 ppm Mo and the highest value was 9.9 ppm. Copper concentrations were low. Fourteen percent of all samples were below 3.0 ppm and 95% of all samples were below 10.0 ppm. Legume feeds had a mean Cu concentration of 7.5 ppm, in contrast to sedge hays which had a mean concentration of 3.3 ppm Cu. As Cu concentrations increased in all feeds the Cu/Mo ratios also increased, when all feeds were considered in one compilation. Molybdenum concentrations were high, then decreased, but increased to the same high concentrations as Cu concentrations increased. These data indicate an unexpectedly high and nutritionally important variability in Cu/Mo ratios, and add further support to our previous report of extensive low levels of Cu. Both Cu and Mo analyses are required to predict the need for Cu supplementation. This appears to be the first extensive report on Cu/Mo ratios in feeds.