Abstract :
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 0.13mgSe kg−1
DM); selenium yeast (SY) as the Se supplement (0.26mgSe head−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
