Heart rate and heart rate variability in multiparous dairy cows with unassisted calvings in the periparturient period - Kovacs, L; Tozser, J; Kezer, F L; Ruff, F; Aubin-Wodala, M; Albert, E; Choukeir, A; Szelenyi, Z; Szenci, O (PHYSIOLOGY & BEHAVIOR, 2015)