Mastitis is the most costly disease of dairy cows. A pro-active approach includes insuring
adequate levels of selective trace minerals. The aim of this study was to determine the effect
of two different commercially available, injectable selenium products, (sodium) Na-selenite
(inorganic) and (selenium) Se-methionine (organic), on milk composition and on serum and
milk selenium concentrations in high-yielding Holstein cows on total mix ration. Sixty
multiparous cows were randomly selected into three groups of 20, one control group and
two groups supplemented with injectable trace minerals. Blood and milk samples were
collected over a period of 60 days. No specific change was indicated in milk yield, lactose,
milk urea nitrogen (MUN) and milk pH levels compared with baseline values. The
Se-methionine supplemented group showed a numerical increase in total milk protein
percentage. In the group injected with Se-methionine, a negative correlation was present for
the initial 72 hours between serum selenium concentration and somatic cell count (SCC) and
a highly significant (p < 0.001) increase in milk selenium concentration for the initial 24 hours.
Serum selenium concentration of Se-methionine-supplemented cows was however not
significantly changed. Injection of Na-selenite led to a 60-day initial increase in serum
selenium concentration above baseline levels and a significant milk selenium concentration
on day 1 but to a negative correlation between serum selenium concentration and SCC.
Differences in serum and milk selenium concentrations followed with the use of organic and
inorganic selenium injectables. Injectable Na-selenite, as selenium, can be of important value
for cattle farmers if supplemented on strategically physiological periods to improve
production, reproduction and immunity.