Fourteen years of accumulated electrical energy use data related to milking operations at the 160-cow University of Tennessee Dairy Experiment Station in Lewisburg, Tennessee were analyzed to quantify relative effects of production -related factors on energy use within the milking center. Energy use was measured for vacuum pumps, refrigeration compressors, water heaters, and an air compressor. These energy use figures were then related to the recorded production parameters: number of cows milked, the amount of milk sold, percent butterfat of the milk, the total pounds of fat corrected milk, and high and low dry bulb temperature by means of multiple regression. Analyses were made on a monthly and yearly basis. Total dairy energy use could not be computed due to numerous non-dairy load components in the Experiment Station that could not be subtracted. It followed logically that number of cows milked, milk production, and weather conditions represented by dry bulb temperature were found to be the major factors affecting energy use. However, no parameter, or combination of parameters, explained in a statistical sense more than 74% of the variability in the recorded energy use by the equipment studied. Quantity, and not quality, of milk produced was the most significant factor affecting energy use, with the number of cows milked and outside temperatures playing lesser roles. Regression results showing that cow numbers was not a factor related to energy use for milk cooling or vacuum pump operation, lead to some questions about the validity of kWh/cow/yr as an energy use indicator. For the 14 years of data available, average EUIs for the vacuum pumps for milking (1.10 kWh/cwt) and the refrigeration compressors for milk cooling (1.02 kWh/cwt) were near the upper range of published reference values (0.4 to 1.19 kWh/cwt and 0.8 to 1.10 kWh/cwt, respectively), while average EUI for water heaters (0.65 kWh/cwt) were well below the published range (0.95 to 1.40 kWh/cwt). The former two results confirm the validity of the published EUIs that were based only on a few year’s data. Interestingly, the results also indicate a general consistency in the year to year operation of similarly sized dairy operations. The lower EUI for the water heater was due to the use of a preheater and also the every-other-day milk collection at the dairy.
