Plansky, Vladimir, and Kalin Hristov. “SEASON OF DELIVERY, AGE OF FIRST FERTILISATION AND MILKING YIELD DURING THE FIRST LACTATION PERIOD OF HEIFERS”. TRADITION AND MODERNITY IN VETERINARY MEDICINE, vol. 5, no. 1, June 2020, pp. 53-57, doi:10.5281/zenodo.3675468.