In four experiments with suckler cows and growing cattle at grass two
sustained release multi-trace element boluses providing, inter alia, 0
.8 mg selenium per day significantly increased initially low blood glu
tathione concentrations over periods in excess of 100 days. Two experi
ments resulted in significant increases in blood haemoglobin concentra
tions. The blood copper concentrations at the start of the summer graz
ing season were at the lower end of the normal scale and giving two bo
luses (providing 140 mg Cu/day) maintained these levels. On one farm t
here was a significant reduction in blood copper concentration for the
untreated cattle after 102 days grazing.