Effect of organic selenium supplementation to ration on some biochemical blood parameters and pregnancy rates of dairy cows in summer and winter season

This study was aimed to investigate the effect of organic selenium added to dairy cows' rations on some biochemical blood parameters and pregnancy rates in summer and winter season. A total of 120 cows, 60 in the summer and winter each, were divided in 4 groups, consisting of 15 cows. The control group was fed with daily rations, and 3 (1st group), 6 (2nd group) and 12 (3rd group) g/day organic selenium was added to the rations of the experimental groups, respectively. This treatment was conducted 40 days before the planned artificial insemination and continued till 20 days afterwards. Malondialdehyde (MDA), glutathione (GSH) and glutathione peroxidase (GSH-Px) levels were determined in all animals at the 0th, 40th and 60th days. No difference was found between MDA levels in winter, but between day 0 and 40 the difference was statistically significant in all groups in summer (P<0.05). It was also found that GSH levels reached to the highest levels on 60th day in all groups during winter period and significant reduction was seen in the 2nd and 3rd groups in summer period (P<0.001). Winter GSH-Px values were significantly decreased in all groups between day 0 and 40, but a significant increase was observed in control group between the same days in summer period (P<0.001). A comparison of winter and summer seasons showed increase in MDA levels in all groups except the 1st group was statistically significant (P<0.05). In winter and summer periods GSH levels were incresed significantly in all groups except control group (P<0.05). GSH-Px values in all groups except the first group were found to be significantly different between summer and winter period (P<0.05). After 4 weeks of artificial insemination ultrasonographic scan was performed. There was no statistical difference in terms of pregnancy rates between the seasons and within groups. In conclusion, short-term supplementation of organic selenium, 12 g/day, increases pregnancy rate by 6.7% in summer and 20% in winter compared with control group. Thus selenium supplementation into the ration can improve pregancy rate during the heat stress. Keywords: Dairy cow, heat stress, pregnancy, selenium.