ABSTRACT. The purpose of this study was to investigate the effects of four types of diets containing different forms of selenium on the hematological blood parameters, reproduction and health of dairy cattle during the transition period. Twenty-four close-up dry cows with a mean of 259 ± 1days of pregnancy and expected 21 ± 1days prior to parturition were selected. The cows were fed four diets: 1) basal diet without selenium supplementation (C); 2) basal diet plus 0.5ppm selenium in the form of sodium selenite (Se-S) 3) basal diet plus 0.5ppm selenium in the form of selenium yeast (Se-Y); 4) basal diet plus 0.5ppm selenium in the form of selenomethionine (Se-M). Blood samples for measuring hematological blood parameters (including lymphocyte, red blood cells, hemoglobin, and hematocrit, MCV, MCH, MCHC and RDWc) were taken at 21 and 10 days before delivery, delivery date, 10 and 21 days after delivery. There was no significant difference in hematological parameters before and after delivery in experimental and control groups. However, in the prepartum period, MCH tended to increase significantly in selenium methionine treatment (p<0.05). Reproductive parameters (including distance to first estrus, insemination indexes and number of open days) and health parameters (including rectum temperature and vaginal content score) have been improved by selenium organic supplements. The results of this experiment showed that feeding organic selenium supplementation in multiparous dairy cow’s diet may improve their health and reproduction.

ABSTRACT. The aim of this study was to determine the effects of supplementing close-up and fresh dairy cows’ diets with sodium selenite or organic sources of selenium (Se) on the dry matter intake (DMI), milk production and composition. Based on their body condition score (BCS), previous lactation milk yield and expected calving date, 24 multiparous Holstein dairy cows were balanced and randomly assigned to 4 experimental treatments. Experimental treatments were: control (basal diet without Se supplementation with 0.10 and 0.15 mg of Se kg-1 DM in close-up and fresh diets, respectively), sodium selenite supplementation (0.50 mg of Se kg-1 DM; Se-S), selenium yeast supplementation (0.50 mg of Se kg-1 DM; Se-Y) and selenomethionine supplementation (0.50 mg of Se kg-1 DM; Se-M). Neither Se supplementation nor Se source affected DMI pre- and postpartum. Milk production and composition were not different across Se sources, but concentrations of Se in milk were 14 and 10% greater for cows fed Se-M and Se-Y than for those fed control, respectively. Cows fed Se-M had lower somatic cell count than control (SCC; 173.11 vs. 318.89 cells × 103 Ml-1). The changes of BW and BCS pre- and postpartum were not affected by treatments over experimental period. The results of present study showed that selenomethionine supplementation compared to other sources decreased SCC in transition cows. In addition, milk Se concentrations increased in Se-Y and Se-M groups more significantly compared to the Se-S group. This indicates that organic Se had better replace inorganic Se for transition dairy cows.

ABSTRACT. The aim of this study was to determine the effects of supplementing close-up and fresh dairy cows’ diets with sodium selenite or organic sources of selenium (Se) on the serum biochemical parameters and antioxidant indicators and Se status. Twenty-four multiparous Holstein dairy cows were balanced by body condition score (BCS), previous lactation milk yield and expected calving date and randomly assigned to 1 of 4 experimental treatments. Treatments were: control (basal diet without Se supplementation), sodium selenite supplementation (0.50 mg of Se kg-1 DM; Se-S), selenium yeast supplementation (0.50 mg of Se kg-1 DM; Se-Y) and selenomethionine supplementation (0.50 mg of Se kg-1 DM; Se-M). Serum Se concentrations were higher for cows in Se-Y (72.34 µg dL-1) and Se-Met (72.34 µg dL-1) than control (59.93µg/dl) and Se-S (64.79µg/dl). The Se supplementation and sources did not affect serum metabolites or indices of antioxidant pre and postpartum, except serum total protein and albumin concentrations. Cows in Se-M had greater serum total protein and albumin concentrations than those in control. The results of present study showed that serum Se concentrations increased in Se-Y and Se-M more effectively than Se-S, indicating that selenomethionine could replace Se-S as an effective organic Se source for transition dairy cows.