The incidence of goitre in newborn lambs from ewes fed fodder radish, rape or Italian ryegrass with or without iodine supplementation
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Date
2011
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Conference Contribution - published
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Abstract
Brassicas are an important forage species on many New Zealand sheep farms. However, glucosinolates present in some brassicas can cause iodine deficiency in lambs when pregnant ewes are fed such crops during
gestation. To investigate the effect of differences in glucosinolate profile of fodder radish and a brassica on ewe thyroid function and incidence of goitre in lambs born to ewes grazing these crops during pregnancy, a 3 x
2 factorial study utilising three diets (Italian ryegrass, fodder radish, rape) and two rates of iodine (I) supplementation (with, without) was conducted. Thyroid hormone (T₃, T₄) response to a thyroid releasing
factor (TRF) challenge in ewes and incidence of goitre in newborn lambs was determined. A mild goitre, based on thyroid weight:lamb weight ratio (g/kg) of >0.4, was recorded only in newborn lambs from ewes fed rape
and the incidence was higher (75% vs 11%) in those without I supplementation. Pregnant ewes grazing radish or rape had the lowest T₃ and T₄ responses to TRF, except in the case of T₄ where there had been I supplementation. Differences in glucosinolate content and composition may explain the differing results for sheep fed radish or rape.
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