Large rotary dairies achieve high cow throughput but are not more labour efficient than medium-sized rotaries

It was hypothesised that large rotary dairies (>60 clusters) are not more operator efficient than medium-sized rotaries (40–60 clusters). This was tested by collecting and analysing milking data, during peak and late lactation, from block calving herds milked in rotary dairies fitted with electronic milk meters. Data were collected from a total of 61 unique farms around New Zealand, with rotary dairies ranging in size from 28 to 80 clusters, for two 5-day periods during spring (September–November 2010; 47 farms; average milk yield 23.1 kg/day) and autumn (February–April 2011; 60 farms; average milk yield 16.4 kg/day). A telephone survey was conducted to collect basic farm details: size, land area, the number of herds managed (including hospital herds), number of operators in the dairy and total labour input. A site visit was conducted to collect data such as the number of bails/stalls over the entrance and exit of the platform. The herd management software on each farm was programmed to record similar fields for each of the six machine manufacturers represented. Variables recorded included cow, date, identification time, bail number, milk yield, milking duration, and average milk flow rate. Calculations were performed to determine the number of cows milked and milk harvested per hour as well as the operator efficiency values for these measures and an estimate of cluster utilisation. Mixed models were used to determine the relationship between the dependent variables, cows milked per hour, milk harvested per hour, cows milked per operator per hour, milk harvested per operator per hour, and cluster utilisation, and the independent variables collected. Cows milked and milk harvested per hour increased linearly with rotary size, during both spring and autumn and there was a quadratic relationship between operator efficiency measures and rotary size, which peaked at ~60 clusters. Cluster utilisation, the amount of time clusters were harvesting milk out of the plant running time, was estimated at 46 ± 6%. Larger rotary dairies on average achieved greater throughput; however, they were not more operator efficient than medium-sized rotaries. Thus, large rotary dairies are best suited to farms where the additional throughput is required.