The effect of iodine supplementation on growth performance, reproductive parameters and thyroid hormones of sheep in some areas of Markazi province, Iran

Iodine is an essential element for the production of thyroid hormones that control the body's metabolism. Subclinical iodine deficiency, which is related to the deficiency of this element in the soil, is likely in most livestock in different parts of the country, especially grazing livestock, and was reported in sheep with plasma inorganic iodine less than 5 Micrograms per deciliter in some areas of Markazi province about 10 years ago. The objective of this study was to re-evaluate the iodine status of sheep in Shazand areas and evaluate the effects of using an injectable iodinated oil supplement on thyroid hormone concentrations, blood serum and milk inorganic iodine content, and the production performance of ewes and their lambs.

Seven sheep breeding farms in this region randomly selected and ewe’s serum inorganic iodine analyzed. To evaluate the effects of iodine supplementation, the herd with the lowest amount of serum inorganic iodine in which the experiment could be performed was considered as the experimental herd. In this herd,80 Farahani ewes with an average weight of 48.53±7.8 was divided into two groups of 40 as control and experimental groups. The experimental group, were supplemented with 1.5 ml iodised oil (Depodine®) intramusculary three weeks before mating and nine weeks later. Concentrations of thyroid hormones including triiodothyronine and thyroxine on days 60 and 120 from start of the test, inorganic iodine in blood serum every month until day 180,inorganic milk iodine after lambing and production and reproductive parameters were measured and compared in the two groups.

The iodine status of the studied herds indicated that iodine deficiency continued in the study area, and this problem was not resolved. The lowest and highest serum mineral iodine levels of the studied herds were 2.0±0.22 and 4.38±2.08 μg/dl, respectively. Thyroid hormone concentrations were significantly (P< 0.05) elevated in the iodine-supplemented ewes after treatment. Serum inorganic iodine and milk inorganic iodine of ewes also increased from 2.39 and 1.22 μg/dl in the control group to 11.2 and 21.44 μg/dl in the experimental group, respectively (P<0.01). The mean birth weight of lambs in the experimental and control groups was 4.33±0.62 and 3.91±0.77 kg, respectively, which had a significant difference (P<0.05). Also, the mean weaning weight of lambs in the experimental group increased compared to the control group (17.08±1.16 and 16.6±1.83 kg, respectively) and lamb survival rate up to day 120 increased significantly (P<0.05) while lambing rate and litter size of ewes didn’t affect.

The results indicate that sheep continue to be impacted by the effects of iodine deficiency in the study area based on low serum mineral iodine concentration, and the effectiveness of the iodine supplement in preventing the effects of iodine deficiency in sheep and improving their production and reproduction performance.