Effect of either sodium selenite or Se-yeast supplementation on selenium status and milk characteristics in dairy goats

This study aimed to determine the effects of dietary Se source on goat's milk and blood Se status, and its subsequent effects on a number of milk characteristics. Ninety lactating dairy goats fed the same basal diet were randomly allocated to 1 of 3 dietary treatments: negative control (CTRL), containing background Se only (dietary concentration of 0.13mg Sekg⁻¹ DM); selenium yeast (SY) as the Se supplement (0.26mgSehead⁻¹ d⁻¹ of Se-yeast individually offered); sodium selenite (SS) as the Se supplement (0.26mghead⁻¹ d⁻¹ of sodium selenite individually offered). The period of supplementation was 112 d. Jugular venous blood samples (before morning meal) and milk samples (a.m. milking) were taken from 10 goats/treatment on d 0, 28, 56, 84 and 112, and milk yields recorded. On d 84 three Italian fresh cheeses were manufactured from bulk milk taken from each treatment. Selenium content of whole blood, plasma, milk and cheese was determined and erythrocyte glutathione peroxidase (GPX-1) activity was also measured. The proportion of Se incorporated as selenomethionine (SeMet) or selenocysteine (SeCys) in pooled whole blood samples was determined on d 0, 56, and 112. Milk samples were analysed for fat, protein, lactose, somatic cell count, thiocyanate and lactoperoxidase activity. Keeping quality of pasteurized milk was measured using pH, clot on boiling and alcohol stability tests. Data were analysed as repeated measures. Both Se sources, when compared to CTRL, increased GPX-1 activity (P <0.05), the Se content of blood (P <0.001) and plasma (P <0.05). However, there were no differences between sources neither on GPX-1 activity nor on the Se content of whole blood and plasma. Despite this lack of difference in total Se in whole blood there were greater increases in blood SeMet contents in SY supplemented animals when compared to CTRL and SS. Milk Se content was only numerically higher in SS when compared to CTRL but greater in SY when compared to both SS and CTRL (P <0.001). Cheese Se content mirrored the Se content of milk. Milk yield and milk characteristics were not affected by Se supplementation. These results seem to indicate a greater efficiency of uptake and incorporation of Se into milk in those animals supplemented with Se-yeast when compared to those receiving comparable doses of selenite.