Annual Periodicity of Total Blood Thyroxine (T₄) in Male Fallow Deer: Problems and Experiences

Abstract

The annual T₄ profile in adult fallow (Dama dama) bucks plateaus between January and August (x-̄ ≈ 50 ng/ml). T₄ has minimal values during the rut (October: x-̄=28.3 ng/ml; November: 30.4 ng/ml) with differences of 44% (P≦ 0.001). There were no differences between serum and plasma samples (P ⩽ 0.001; r>0.9). Annual profiles with two commercial kits show r = 0.98, but differences of 33.1% to 34.6% (P ≤ 0.001). T₄ measurement was repeated later with the same blood samples and the same coded test kit. Results showed r = 0.94, but values differed at 10.14 ng/ml (P ≤ 0.001). Other values were also lower in this test. One yearling fell sick and 4 weeks before death T₄ = 14.9 ng/ml. Another buck had a severe parasitic infection, but in conjunction with a social environment change, T₄ almost normalized after 1 year. T₄ measurements were made in animals that had lived together more than 1 year before sampling. R over 1.5 years were: 0.89, 0.79, and 0.85 between half-brothers, and 0.73, 0.79, and 0.86 between adult bucks. Annual T₄ curves of other bucks from other groups had faint positive correlations with the two groups mentioned, but all individuals demonstrated a strong T₄ depression around rut. The annual T₄ pattern in a fawn/yearling living in a small enclosure with several old animals showed extremely high T₄ due to the social stress. There was no difference in T₄ between fawns/yearlings and adults, but in fawns/yearlings T₄ oscillated.