Lack of iodine has been implicated with poor lamb survival at birth, due to new-born lambs being more susceptible to chilling and exposure as they are less able to control body temperature. While we have generally failed to identify iodine problems in sheep grazing pasture, pre lamb we have seen problems with pregnant sheep grazing brassica crops.
Our general recommendation is that if you graze pregnant sheep on brassica in the second half of pregnancy they should be treated with an oral iodine drench as they go onto the crop and again as they come off the crop if they are on crop for more than 3 weeks.