Summer Season-Related Heat Stress Affects the Mineral Composition of Holstein Dams' Colostrum, and Neonatal Calves' Mineral Status and Hematological Profile.

This study examines the effect of season-related heat stress in dams on mineral status, and hematological profile of their calves. Ten Holstein dams (LowT group) were exposed to the 49-day-long period of low air temperature (5.2 ± 0.5 °C) and ten dams (HighT group) were exposed to a 53-day-long high air temperature (27.4 ± 0.4 °C). The dams' blood samples were taken one hour after parturition, while colostrum was sampled at 2, 14, and 26 h after calving. Ca, P, Mg, Na, K, Fe, Zn, Mn, and Se concentrations were significantly lower while Cu and Co concentrations were significantly higher at least in two examined colostrum sampling points in HighT group. Calf`s blood samples were taken before 1st colostrum intake, and on days 1, 2, 3, and 7 postnatal. Ca, P, Na, K, Fe, Cu, Zn, Mn, Se, and Co were significantly lower while concentration of Mg was significantly higher in calves that originated from HighT group at least at two examined sampling points. Season affected dam's blood mineral status but the pattern was not always the same as in calves, since Na, K, Cu, and Co were significantly higher in HighT group. Calves that originated from HighT group had significantly lower hemoglobin, hematocrit, MCV, MCH, and MPV values, as well as neutrophils and monocyte counts, while platelets, eosinophils, basophils, and lymphocyte counts were significantly higher. Season-related heat stress leads to a reduction of the most minerals in both dams' colostrum and calves' blood and certain minerals' deficiencies are linked to impaired calves' hematological adaptation.