Abstract

Iodine supplementation before mating had a significant positive effect on ewe fertility in a Manawatu Romney flock, with 14% more lambs born to supplemented than to control mixed aged ewes. The survival of newborn lambs was enhanced in the iodine-supplemented group when compared with the control group, accompanied by a significant difference between the thyroid:body weight ratios of dead newborn lambs in the supplemented and control groups (0.28 and 0.48 g/kg respectively)(p=0.005). During the spring of 1997, high perinatal lamb mortality rates (25%, 50% and 66%), despite favourable lambing weather conditions and adequate ewe nutrition throughout pregnancy, were investigated in three other Manawatu sheep flocks. The mean lamb thyroid:body weight ratios of dead newborn lambs were greater than 0.4 g/kg and hyperplastic colloid goitre was identified histologically. Goitrogens in the pasture were believed to be an important predisposing factor. Modern varieties of white clover present in New Zealand pastures contain extremely high concentrations of thiocyanate goitrogen precursors, therefore, iodine deficiency may be an emerging problem.

ND, Sargison, and DM West

Proceedings of the New Zealand Society of Animal Production, Volume 58, , 202-204, 1998