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Iodine Nutrition and Thyroid Function of Ewes and Lambs on Orchardgrass under Different Levels of Nitrogen and Micro-Element Fertilization^{1, 2,}

West Virginia University, Morgantown 26505

Abstract

Experiments described were conducted to define thyroid abnormalities observed in lambs from ewes grazing orchardgrass fertilized at various levels of nitrogen (N) fertilizer or N plus trace elements. Four fertilizer treatments (56kg N/ha; 168 kg N/ha; 504 kg N/ha; 504kg N/ha + Co, Cu, Mo, Zn and S) were applied to replicated hay and pasture plots of Potomac orchardgrass. Seventy-two western ewe lambs were allocated randomly to fertilizer treatment groups and maintained on pasture and hay from 1967 to 1971. In autumn, 1970, one half of the ewes on each fertilizer treatment received supplemental iodine.

Forage iodine concentrations indicated marginal deficiency conditions. The N fertilization level had no effect on iodine concentrations of herbage or hay.

Serum thyroxine levels of ewes were not affected by fertilizer treatment or by iodine supplementation. ¹³¹I uptake trials with ewes in the autumn and winter of 1970 indicated a greater uptake by unsupplemented ewes than by iodine-supplemented ewes. Histological examination of ewe thyroid glands in 1971 revealed hypertrophy and hyperplasia of the follicular epithelium.

Gross thyroid enlargement in newborn lambs was observed in spring, 1969, but not in subsequent years. In 1968, thyroid weights and follicular cell heights from slaughtered lambs, and palpation data from lambs remaining with their dams, suggested that goiter was most severe and most prevalent on high N fertilizer treatments. In 1969 and 1970 there was no apparent relationship between level of N fertilization and the occurrence of lamb thyroid dysfunction.

¹ Published with the approval of the Director of the West Virginia Agricultural Experiment Station as Scientific Paper No. 1290.

² The authors wish to express their appreciation to E.C. Townsend for advice on statistical analysis of the data. The study was carried out with financial support from HEW, PHS Grant No. ES 00150-02; microelement fertilizers were supplied by TVA.

³ Present address: Agricultural Research Service, U.S. Department of Agriculture, Fort Reno Livestock Research Station, El Reno, Oklahoma 73036.

⁴ Present address: U.S. Regional Pasture Research Laboratory, U.S. Department of Agriculture, University Park, Pennsylvania 16802.