Significance of Amount and Form of Dietary Selenium on Blood, Milk, and Casein Selenium Concentrations in Grazing Cows

Abstract

Organic selenized yeast enriched with selenoamino acids or inorganic sodium selenate (Na2SeO4) was administered per os three times weekly as a drench for 133 d to previously unsupplemented cows that were grazing low Se pastures. Treatment groups received the equivalent of 2 or 4 mg of Se/d of either supplement form. Control cows did not receive a drench. Samples of blood and milk were collected regularly throughout the trial. Selenium concentrations in blood, milk, casein, and liver and glutathione peroxidase activity in blood and liver are reported as responses per milligram of Se intake. Mean blood Se concentrations in treated cows increased steadily and, by d 133, were 4.7 to 8.8 times that in controls. Selenized yeast was 2 to 3 times more effective than was Na2SeO4, and low Se intakes were 27% more efficient per milligram of Se administered than were high Se intakes at increasing milk Se concentration. Casein Se content mirrored that of milk; among all treated and control cows and throughout the trial, the molar ratio of Se in casein as a percentage of the Se in whole milk was constant at 71 +/- 1.2%. The Se concentration in liver biopsies taken on d 133 was indicative of total Se intake during the trial and ranged from 920 to 3920 nmol of Se/kg of fresh weight. These results demonstrate the differing efficacy of organic and inorganic Se dietary supplements to increase dairy cow Se status and to enhance Se content of milk and casein.

Iodine and selenium carry over in milk and cheese in dairy cows: effect of diet supplementation and milk yield

“…The selenium content in milk from T2 cows (23.4 mg/l) was numerically similar to values reported by Juniper et al (2006) on cows fed either SY or sodium selenite (27.8 and 20.8 mg/l in milk from cows fed 0.27 and 0.25 mg/kg DM of selenium as SY or sodium selenite, respectively). In our condition, when supplementing selenium, the CO rate decreased as expected (Knowles et al, 1999), whereas the plasma selenium concentration increased to values that are in agreement with Maus et al (1980) since T2 cows were fed about 6 mg/day of selenium and were showing a plasma content of selenium higher than 80 mg/l.…”

“…Our partition of the selenium into curd supported data from Knowles et al (1999) on the casein fraction, thus the selenium was a more suitable element to produce enriched hard cheese through supplemented animal feedstuffs than iodine. When considering a daily intake of 150 ml of milk per head, for an RDA of 8, 20 and 35 mg selenium/day, the milk from T2 cows would provide 44, 18 and 10% of the RDA, respectively, for infants, children and adults.…”

“…The increment of the selenium concentration in milk was nonlinear as reported previously (Knowles et al, 1999). Our data showed a maximum level (about twofold higher than the control) already at day 3, with plateau at day 10 until the end of the trial (Figure 1b), whereas in previous works, the selenium concentrations in milk and plasma tend to remain at steady condition in about 1 to 2 weeks after supplementation (Heard et al, 2007) and reach their maximums in about 40 days (Conrad and Moxon, 1979).…”

“…Generally, bovine milk ranges between 5 and 56 mg/l (Underwood, 1971) in relation to selenium content of feeds and soil. The selenium fortified feeds, either from inorganic (sodium selenite and selenate) and organic (selenized yeasts) sources, have been fed to cows to improve the milk selenium content (Knowles et al, 1999;Givens et al, 2004).…”

“…Cheese could be an important source of iodine and selenium; however, there are few studies dealing with the partition of these elements into the curd and casein fractions (Sieber, 1998;Knowles et al, 1999).…”