Variability in mineral and trace element content of dairy cattle feeds.

Trace element content of feeds is extremely variable compared to total digestible nutrients or protein. Differences are wide between low and high values for many trace elements within a given type of feed. Coefficients of variation for forages range from 42 to 100%. Summary data are given for both major and trace elements. Problems in supplementation are discussed. Amounts for some elements are skewed with relatively few samples around the mean and over 60% below the mean. Suggested mineral allowances for dairy cows are listed. Under current supplementation, zinc is the trace element most likely to be limiting and manganese the least likely. Iron, copper, cobalt, and iodine may be limiting in some cases. Needs of research and applied nutrition are presented.