Research forces re-think on pregnant ewe supplementation
Take Home Message: Excess iodine in the diet of pregnant ewes reduces the ability of lambs to absorb antibodies from colostrum, potentially increasing the risk of disease.
Offering ewes 26.6mg of iodine for one week prior to lambing will have negative effects on their lambs’ absorption of colostral IgG to 24 hours and 72 hours post partum and on serum vitamin E concentration at 72 hours post partum – a period of supplementation that is much shorter than previously reported.
“And offering cobalt at a rate of 20mg per ewe per day also leads to a breakdown in the transfer of vitamin E from colostrum to the serum of the newborn lamb,” said University College Dublin’s Thomas Boland, who led a team of researchers who investigated the effect of cobalt and iodine supplementation of the pregnant ewe diet on immunoglobulin G, Vitamin E, T3 and T4 levels in the progeny
Sixty twin-bearing ewes were allocated to one of four dietary treatments investigating the effects of supplementary iodine or cobalt during late pregnancy on lamb serum immunoglobulin G (IgG), triiodothyronine (T3), thyroxine (T4) and vitamin E concentrations, and lamb IgG absorption efficiency.
Ewes were offered ad-lib grass silage supplemented with 800g per ewe per day of a 190g/kg crude protein (CP) concentrate from day 126 of gestation until lambing, plus one of the following supplements: no supplement; 26.6mg of iodine per day for the final three weeks before lambing; and 26.6mg of iodine per day for the final week before lambing; and 20mg cobalt per day for the final three weeks before lambing.
Lambs were blood sampled at 24 hours and 72 hours post partum for serum IgG and vitamin E concentrations.
“And we found that supplementing the ewe’s diet with 26.6mg/day of iodine for the final week of pregnancy reduced lamb serum IgG concentration at 24 hours and 72 hours post partum,” said Dr Boland.
“The lower total and free T3 values in the progeny of ewes fed 26.6mg/day of iodine for the final three weeks of pregnancy suggest interference in the synthesis and metabolism of thyroid hormones when ewes receive excessive dietary iodine for three weeks immediately pre partum.
“Based on these findings, the indications are that the toxicity level for iodine in the diet of the pregnant ewe should be lowered to 20mg per ewe per day – equivalent to 40% of its current level,” he added.
Full details: Boland TM, Layes L, Sweeney T, Callan JJ, Baird AW, Keely S and Crosby TF: “The effect of cobalt and iodine supplementation of the pregnant ewe diet on immunoglobulin G, Vitamin E, T3 and T4 levels in the progeny.” Animal 2: 197-206.
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