Żuk, Józef, and Robert Orzechowski. “The Influence of System of Breeding on Labor-Consumption and the Optimum Scale of Production of Milk in Agricultural Farms”. Annals of Agricultural Economics and Rural Development, vol. 96, no. 4, Dec. 2009, pp. 277-89, doi:10.22630/RNR.2009.96.4.90.