Principles for maximising operator efficiency and return on investment in rotary dairies

Abstract

This study quantified the effect of rotary size, platform speed, cluster attachment time, milk yield and end-of-milking criteria on cow throughput, operator efficiency and return on investment. A model was developed to predict the mean and standard deviation of cow milking duration for a given milk yield using milking data collected from commercial dairy farms in New Zealand. After accounting for the effect of end-of-milking criteria, this estimate was used to calculate the expected cow throughput and operator efficiency for a given platform speed, rotary size and cluster attachment time. The economic return of investing in rotaries of 44–80 bails, relative to a 40-bail rotary, was evaluated using a 25-year internal rate of return. The economic return of installing automatic cluster removers (ACR) was also examined. Estimated cow throughput increased with increasing platform speed and ACR threshold for a 50-bail rotary (a common rotary size) and the largest single gain in cow throughput came from changing the ACR threshold from 0.2 to 0.4 kg/min. Further increases had less impact, especially at lower platform speeds. However, for larger rotaries, maximum operator efficiency could be achieved using a variety of platform speeds and end-of-milking criteria. A larger rotary was required to achieve maximum potential operator efficiency, for a given cluster attachment time, as milk yield was increased. Increasing the minimum cluster attachment time decreased maximum potential operator efficiency. Consequently, operator ability and anticipated milk yield are key parameters when selecting the number of bails in a new-build rotary. Seventy- and 80-bail rotaries were generally not more operator efficient than 60-bail rotaries. Economically, the 50-bail rotary allowed the greatest labour saving per dollar invested for a typical farm conversion in Canterbury, New Zealand, although the ultimate choice of rotary size depends on the individual farm situation. The internal rate of return for installing ACR decreased with increasing rotary size, but was always positive. Farmers should carefully evaluate their options before investing in a new rotary.