Iodine distribution in the environment as a limiting factor for roe deer antler development

The iodine-containing hormones produced by the thyroid gland play a role in the complex neuro-hormonal regulation of antler development. The proper function of the thyroid depends on the adequate iodine supply of the organism, which is directly related to the iodine content of food and drinking water. The purpose of this study was to explore the connection between the iodine content of the water base, which has a strong correlation with the iodine concentration of environmental components available to animals, and the antler weight of roe deer (Capreolus capreolus) shot in Hungarian hunting areas. Using a general linear model, controlling for the collective effects of other environmental factors (deer population density, harvest rate, land use, and soil fertility information), the iodine content of the water base explained 51.4% of the total variance of antler weights. The results suggest that antler weights increase with increasing iodine concentration regardless of other factors; thus, the environmental iodine distribution can be a limiting factor suppressing roe deer performance assessed here as antler weight. Further experimental studies of controlled iodine uptake are needed to define the exact physiological iodine requirements of roe deer bucks.

Seasonal levels of cortisol, triiodothyronine and thyroxine in male axis deer

1. Seasonal plasma levels of thyroxine (T4), triiodothyronine (T3) and cortisol were investigated between November and June in seven penned male Axis deer. 2. No distinct seasonal variation of cortisol has been detected. The levels oscillated between 1 and 5 micrograms/dl. 3. The stress of immobilization and sampling had little effect on cortisol levels. Concentrations remained mostly stable in three consecutive samples taken 10 min apart. 4. T3 concentrations were stable between November and March (average values 110-120 ng/dl). After a sharp decline in April (average 70 ng/dl), a strong rebound in May and June was observed. 5. A distinct seasonal peak of T4 (highest individual value, 12.1 micrograms/dl) was detected in March. After a sharp decline in April (lowest individual value, 4.5 micrograms/dl) a strong rebound followed in May.