Huculak, G. 2019. Dependence of milk productivity Holstein cows on the duration of lactation period and organism’s physiological activity. Bulletin of Sumy National Agrarian University. The series: Livestock. 1-2(36-37) (Jul. 2019), 54-57. DOI:https://doi.org/10.32845/bsnau.lvst.2019.1-2.8.