Detrimental effects of iodine deficiency on ovine gametogenesis and replication

Damaged reproduction, including miscarriages and stillbirths, represents a major issue of the iodine deficiency disorders (IDD) affecting humans and animals living in iodine deficient environment. Moreover, during the last decade, a number of different experimental findings suggested an important role for thyroid hormone in male and female gonadal development and gametogenesis. In the present study, we monitored the reproductive capacity of sheeps exposed to iodine deficiency or following iodine prophylaxis. To this end, 40 ewes and 20 rams, characterized by low urinary iodine concentrations (UIC) (78.2±6.3 g/L) were used. The animals were ramdomly divided into two groups. One group (20 ewes and 10 rams) received a subcutaneous injections of 1 ml of Lipiodol (containing 480 mg of iodine), while the remaining animals were used as control group. This single injection was able to maintain UIC well above 300 g/L for at least 3 months and to induce a statistically significant increase in both T4 (69.8±17.9 ng/ml vs 48.4±10.7 ng/ml, P<0.01) and T3 (1.13±0.27 ng/ml vs 0.69±0.30 ng/ml, P<0.01) serum levels. After 6 months reproductive capacity was assessed by monitoring the rate of successful matings, compared to that of untreated animals. To this end, treated and untreated ewes were mated for 5 days with lipiodol-treated and untreated rams, respectively. Successful matings were evaluated by monitoring, 1 month later, the presence of embryos by ecographic analysis. The results showed that 100% of treated ewes mated with treated rams were pregnant, while only 37% of the control ewes mated with control rams were pregnant (P=0.007). During pregnancy, 1 miscarriage in both control and treated animals was observed. At birth, body weight and height were similar in lambs born from control and treated ewes. One month after labor, control ewes showed an increased thyroid/body weight ratio with respect to treated ewes (8.5±0.7 x 10-5 vs 6.4±0.5 x 10-5, P<0.05). Histological analysis of adult male and female gonads showed that gametogenesis was impaired in control animals with respect to the treated ones. In conclusion, the results of the present study suggest that iodine deficiency may have adverse effects on ovine gametogenesis and explain the reduced animal fertility observed in iodine deficient environment.