Selenium (Se) absorption was studied in human milk, bovine milk and infant formula (Similac) using suckling rats as a model. The effect of age on Se absorption from the three milk diets extrinsically labeled with 75Se, either as selenite or selenomethionine, was also investigated. Milk diets were fed by gastric intubation and the radioactivity in the carcass, gastrointestinal tract and the liver were measured 3 h after feeding. There was no difference in [75Se]selenite absorption from the three milk diets between 8-20 d of age. However, significantly higher quantity of 75Se was absorbed from all three milk diets by 20-d-old rats than by the younger rats (46 vs. 32%). This increase in [75Se]selenite absorption with advancing age is opposite to what has been found for most other trace elements. When rats were fed milk diets labeled with [75Se]selenomethionine, the absorption of 75Se was approximately twofold higher in all age groups compared with 75Se absorption from selenite. No difference in [75Se]selenomethionine absorption existed among the three milk diets in 8- or 10-d-old suckling rats. However, at 15 d of age [75Se]selenomethionine absorption from human milk was higher (82%) than from either bovine milk (72%) or infant formula (72%). Between 8 and 20 d of age, absorption of [75Se]selenomethionine from the three milk diets decreased with advancing age. Adding sodium selenate to increase the total nonradioactive Se of human milk, bovine milk (endogenous plus the added selenium) did not affect the absorption of either [75Se]selenomethionine or [75Se]selenite.

1. Very little is known about the biological availability of manganese from human milk and other infant milk diets. To determine the relative Mn availability, and to examine whether the age and the duration of previous fasting affect Mn absorption, sucking rats were given human milk, bovine milk and infant formula (regular Similac; Ross Laboratories, Columbus, OH) extrinsically labelled with 54Mn.2. Milk diets were given by gastric intubation and the radioactivity of the carcass, liver and digestive tract was measured 3 h after feeding.3. The concentration of endogenous Mn was lowest in human milk (7-10,ug/l) and highest in rat milk (1W165 ,ug/l). Increasing the non-radioactive total Mn concentrations of either human milk or bovine milk up to 150 pg/l did not affect the absorption of 54Mn by 10-d-old rats.4. No significant ( P > 0.05) difference in 54Mn absorption was found among the three milk diets (human milk, bovine milk, infant formula) in 8-to 1 1-d-old rats. However, significantly more ( P < 0.05) 54Mn was absorbed from human milk and infant formula than from bovine milk when 13-d-old rats were used.5. 54Mn radioactivity detected in carcasses of 8-, 9-, 10-and 1 1-d-old rats ranged from 25 to 27% of the dose frbm various milk diets. The activities of 54Mn in the carcasses of 13-d-old rats were 15, 11, and 16% of the dose from human milk, bovine milk and infant formula respectively.6. The trend of 54Mn incorporation into liver was similar to that of the carcass and over 60% of the absorbed 54Mn was incorporated into the liver regardless of the type of milk used.7. Absorption of 54Mn from extrinsically labelled rat milk using 9-or 10-d-old sucking rats was similar to its absorption from infant formula.8. The absorption of 54Mn from the three milk diets decreased with age of the neonatal rats and 54Mn absorption from human milk, bovine milk, infant formula as well as rat milk was affected similarly by duration of previous fasting.

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