Metabolic and hematological profiles in heat stressed lactating dairy cows fed diets supplemented with different selenium sources and doses

This study was conducted to determine the effects of either dietary selenium (Se) source or dose on a range of dairy cow metabolic and hematological profiles and their subsequent relationship with oxidative status and environmental temperature. Forty lactating cows, offered the same basal diet, were blocked by days in milk, milk yield and parity and then randomly allocated to 1 of 5 dietary treatments: negative control (CTRL; 0.098 mg Se kg− 1 DM), two levels of Se yeast (SY) supplementation (0.31 and 0.50 mg total Se kg− 1 DM), and two levels of sodium selenite (SS) supplementation (0.31 and 0.50 mg total Se kg− 1 DM). Whole blood samples were taken from all animals at the start of the study (23 March) and after 28, 56, 84, 112, 126, and 140 d. Whole blood samples were analyzed for total Se, glutathione peroxidase (GPX-1) and a range of hematological parameters. Plasma was analyzed for total Se, glutathione peroxidase (GPX-3), metabolites related to energy and protein metabolism, concentration of minerals, enzyme activities, positive acute phase proteins and oxidative status markers. Glutathione peroxidase activity and total Se in whole blood and plasma were greater (P<0.001) in Se supplemented cows than CTRL. The temperature humidity index (THI) values indicate that during the trial cows experienced a slight-mild heat stress. A negative effect of THI on plasma glucose, non-esterified fatty acids (NEFA), thiol groups, plasma Na and K, and leukocyte count was observed. Conversely, a positive effect of THI on aspartate aminotransferase (AST) activity and GPX-3 activity was observed. Lower values (P<0.05) of thiobarbituric acid reactive substances (TBARS) during the hotter period were observed in SY supplemented animals when compared with CTRL and SS. Furthermore, plasma total antioxidants were lower (P<0.05) in SY supplemented animals when compared with SS during the hotter period. Plasma reactive oxygen metabolites were also numerically lower in SY when compared to SS. These results could be interpreted as an improvement in the preventive antioxidant systems of cows fed Se yeast.