The nutritional value of any particular raw material or forage is not the same for all batches used in animal feeds. For example, the ruminant energy concentration for rolled wheat used in a particular mill over a six month period may have a mean value of 13.5 MJ ME/kg DM but, for any given diet formulation during that six month period, there will be some variation around this mean value The degree of uncertainty may be expressed as a credibility interval (an interval within which there is a specified probability that the true value lies) or, assuming a normal distribution, as a standard deviation (SD) or variance (SD2).