The transfer of different forms of 35S to goat milk

Sulphur-35 is released during the routine operation of UK gas-cooled reactors. An experiment to determine the rates of transfer of different forms of 35S to goat milk is described. Lactating goats received 35S orally as single administrations of sulphate, l-methionine, or grass contaminated either through root uptake of 35S as sulphate or through aerial deposition of 35S as carbonyl sulphide onto the grass. Transfer was higher for 35S administered as methionine compared with 35S administered as sulphate. Changes in activity concentrations in milk for all sources of 35S demonstrated two components of loss. The first component had a half-life of circa 1 d for all sources, the second was longer in goats administered carbonyl sulphide (44 d) than in all of the other treatments (circa 10 d). The rate of transfer of 35S to milk of a further group of goats receiving 35S-sulphate daily appeared to reach equilibrium within 30 d. Extrapolation of transfer parameters derived to other dairy ruminants is discussed.