Seasonal changes in growth rate, feed intake, growth hormone, and thyroid hormones in young male reindeer (Rangifer tarandus tarandus)

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Abstract
The levels of thyroxine (T4), triiodothyronine (T3), and growth hormone (GH) in blood serum from young male reindeer have been measured and compared with changes in body weight and feed intake during ad libitum and restricted feeding. All three hormones fluctuated during the year. T3 changed in response to changes in feed intake. T4 and GH seemed to have basic seasonal patterns, which were modified by differences in feed intake. GH rose to high levels in late winter – early spring. T4 levels were higher in summer than in winter, corresponding roughly to changes in weight gain and feed intake.