1. Effects of selenium yeast on rumen fermentation, lactation performance and feed digestibilities in lactating dairy cows C. Wang A, Q. Liu A,, W.Z. Yang A,B, Q. Dong A, X.M. Yang C, D.C. He C, P. Zhang D, (July 2009) Presented by AbouBaker Elhajee

2. Introduction Selenium is recognized as an essential trace element. It is a powerful catalytic element constituting the active centre of about 20 selenoproteins Selenium displays metabolic function related to maintenance of integrity and defenses of the organism.

3. Supplementation Se content within plants can be extremely variable. Consequently, selenium in diets can be deficient. Se supplementation may be required to improve the performance and health of dairy, enhance the nutritional quality of the milk product

4. Forms Inorganic Se (i.e., sodium selenite or selenate) and organic Se (i.e., selenium-yeast [SY]). Most studies reported that organic Se is less toxic than inorganic Se, Bioavailability of SY higher than inorganic Se sources, leads to higher Se content in milk.

5. Results of SY on milk yields and milk components from literature are inconclusive. These contrasting results could be due to differences in the composition of the diet and/or to the dose of SY and lactation period of dairy cow (Juniper et al., 2006)..

6. Objectives The aim of this work was to evaluate the effects of SY supplemented dose on rumen fermentation, lactation performance, milk selenium content and feed digestion in mid- lactation dairy cows.

7. Materials and methods Animals and experimental design. - Twenty-eight Holstein dairy cows were assigned to a replicated 4×4 Latin square. - Treatments were: control, LSY, MSY and HSY with 0,150, 300, and 450 mg SY per kg of (DM) respectively. - Experimental periods were 45 days with 30 days of adaptation and 15 days of sampling.

8. Dry matter intake, milk yield, milk components and milk selenium. - Feed offered and refused were measured daily for each cow (DM intake). - Milk yields were recorded daily. - Milk Samples for analysis of milkcomposition and measure milk Se concentration.

9. Rumen pH and fermentation characteristics. - were measured on two consecutive days at the beginning (days 1 and 2) and end (days 44 and 45) of each period. At 0, 3, 6, and 9 h after the morning feeding, samples (about 100 mL) of rumen fluid were obtained anaerobically via the esophagus using a stomach tube - Ruminal pH was immediately measured using an electric pH meter

10. Rumen pH and fermentation characteristics. -Samples were then strained through four layers of cheesecloth. Five milliliters of filtrate was preserved by adding 1 mL of 250 g/L (w/v) meta-phosphoric acid to determine acetate, propionate and butyrate, and 5 mL of filtrate was preserved by adding 1 mL of 20 g/L (w/v) H2SO4 to determine NH3.

11. Apparent digestibility in the total tract -Cows were dosed via the esophagus with 5 g of chromic oxide per day per cow in two equal proportions at 07:00 and 19:00 h from days 23 to 43 of each period as a digestion marker.. -fecal samples were collected from the rectum of each cow during days 31 to 43 of each period.

12. Results Ruminal pH and fermentation. -There was no significant difference in ruminal pH. -Ratio of acetate to propionate was lower for LSY, MSY and HSY than for control

13. Dry matter intake, milk yield, milk components and milk selenium -Dry matter intake was not affected. -Milk yields were higher for LSY and MSY than for HSY and control -Milk selenium content was linearly and quadratically increased as increasing SY supplementation.

14. Digestibility in the total tract. Were higher for LSY and MSY than for control and HSY.

15. Conclusion Increasing supplementation of cow diet with selenium yeast from 150 to 300 mg/kg dietary DM compared with control increased milk yield and 4% FCM. Improved milk production was likely due to the increased total digestibilities of feeds since DMI was not affected. The further increase of SY dose from 300 to 450 mg/kg dietary DM was not beneficial

16. Recommendation Selenium yeast modulates the digestive microorganisms or enzymes in a dose- dependent manner and the optimum SY supplemented dose was about 300 mg/kg in the present experimental conditions. SY supplementation in the diets of lactating dairy cows could be an efficient way to increase milk Se content.

17. وشكرا على حسن الإستماع